View source for Alan Turing

{{Short description|English computer scientist (1912–1954)}}
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{{Infobox scientist
| name              = Alan Turing
| honorific_suffix  = {{post-nominals|country=GBR|size=100%|OBE|FRS}}
| image             = File:Alan Turing (1951).jpg
| caption           = Turing in 1951
| birth_name        = Alan Mathison Turing
| birth_date        = {{Birth date|df=y|1912|6|23}}
| birth_place       = [[Maida Vale]], London, England
| death_date        = {{Death date and age|df=y|1954|6|7|1912|6|23}}
| death_place       = {{Nowrap|[[Wilmslow]], Cheshire, England}}
| death_cause       = [[Cyanide poisoning]] as an act of [[suicide]]{{efn|group=note|Turing's death was officially determined as a suicide by an [[inquest]], but this has been disputed.}}
| alma_mater        = {{Indented plainlist|
* {{nowrap|[[University of Cambridge]] <!--[[King's College, Cambridge]] doesn't award degrees--> ([[Bachelor of Arts|BA]], [[Master of Arts (Oxford, Cambridge, and Dublin)|MA]])}}
* [[Princeton University]] ([[PhD]])
}}
| known_for         = {{Flatlist|
* [[Cryptanalysis of the Enigma]]
* [[Turing's proof]]
* [[Turing machine]]
* [[Turing test]]
* [[Unorganized machine|unorganised machine]]
* [[Turing pattern]]
* [[Turing reduction]]
* "[[The Chemical Basis of Morphogenesis]]"
* [[Quantum Zeno effect|Turing paradox]]
}}
| prizes            = [[Smith's Prize]] (1936)
| field             = {{Flatlist|
* [[Logic]]
* [[mathematics]]
* [[cryptanalysis]]
* [[computer science]]
* [[mathematical and theoretical biology]]<ref name=googlescholar>{{Google scholar id}}</ref>
}}
| work_institutions = {{Plainlist|
* [[University of Manchester]] 
* [[Government Code and Cypher School]]
* [[National Physical Laboratory (United Kingdom)|National Physical Laboratory]]
}}
| thesis_title      = Systems of Logic Based on Ordinals
| thesis_url        = https://web.archive.org/web/20121023103503/https://webspace.princeton.edu/users/jedwards/Turing%20Centennial%202012/Mudd%20Archive%20files/12285_AC100_Turing_1938.pdf
| thesis_year       = 1938
| doctoral_advisor  = [[Alonzo Church]]<ref name="mathgene">{{MathGenealogy|id=8014}}</ref>
| doctoral_students = {{Plainlist|
* [[Robin Gandy]]<ref name="mathgene"/><ref name=gandyphd>{{cite thesis|degree=PhD|title=On axiomatic systems in mathematics and theories in physics|first=Robin Oliver|last=Gandy|year=1953|url=https://www.repository.cam.ac.uk/handle/1810/245090|id={{EThOS|uk.bl.ethos.590164}}|publisher=University of Cambridge|doi=10.17863/CAM.16125|access-date=9 December 2017|archive-url=https://web.archive.org/web/20171209152236/https://www.repository.cam.ac.uk/handle/1810/245090|archive-date=9 December 2017|url-status=live}} {{free access}}</ref>
* [[Beatrice Worsley]]<ref name="bowen19">{{cite book| first=Jonathan P. |last=Bowen |title=Engineering Trustworthy Software Systems | author-link=Jonathan Bowen | chapter=The Impact of Alan Turing: Formal Methods and Beyond | editor1-last=Bowen | editor1-first=Jonathan P. | editor2-last=Liu | editor2-first=Zhiming | editor-link2=Zhiming Liu (computer scientist) | editor3-last=Zhang | editor3-first=Zili | series=[[Lecture Notes in Computer Science]] | volume=11430 | pages=202–235 |year=2019 | publisher=[[Springer Nature|Springer]] | location=Cham | doi=10.1007/978-3-030-17601-3_5 |isbn=978-3-030-17600-6 |s2cid=121295850 |url=http://researchopen.lsbu.ac.uk/3224/1/setss2018.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://researchopen.lsbu.ac.uk/3224/1/setss2018.pdf |archive-date=9 October 2022 |url-status=live }}</ref>}}
| signature         = Alan Turing signature.svg
}}

'''Alan Mathison Turing''' ({{IPAc-en|ˈ|tj|ʊər|ɪ|ŋ}}; 23 June 1912&nbsp;– 7 June 1954) was an English [[mathematician]], [[computer scientist]], [[logic]]ian, [[cryptanalyst]], [[philosopher]] and [[theoretical biologist]].<ref>{{cite web |title=Alan Turing |url=https://www.bl.uk/people/alan-turing |url-status= |archive-url=https://web.archive.org/web/20190723191531/https://www.bl.uk/people/alan-turing |archive-date=23 July 2019 |access-date=29 July 2019 |publisher=The British Library}}</ref> He was highly influential in the development of [[theoretical computer science]], providing a formalisation of the concepts of [[algorithm]] and [[computation]] with the [[Turing machine]], which can be considered a model of a general-purpose [[computer]].<ref name="frs">{{Cite journal
| last1 = Newman | first1 = M.H.A.
| author-link = Max Newman
| doi = 10.1098/rsbm.1955.0019
| title = Alan Mathison Turing. 1912–1954
| journal = [[Biographical Memoirs of Fellows of the Royal Society]]
| volume = 1
| pages = 253–263
| year = 1955
| jstor = 769256
| s2cid = 711366
| doi-access = free
 |issn = 0080-4606}}</ref><ref name="AFP">{{cite news |last=Gray |first=Paul |date=29 March 1999 |title=Computer Scientist: Alan Turing |magazine=Time |url=http://www.time.com/time/magazine/article/0,9171,990624,00.html |url-status=dead |access-date=10 January 2011 |archive-url=https://web.archive.org/web/20110119181237/http://www.time.com/time/magazine/article/0,9171,990624,00.html |archive-date=19 January 2011 |quote=Providing a blueprint for the electronic digital computer. The fact remains that everyone who taps at a keyboard, opening a spreadsheet or a word-processing program, is working on an incarnation of a Turing machine.}}</ref><ref>{{Harvnb|Sipser|2006|p=137}}</ref> Turing is widely considered to be the father of theoretical computer science.<ref>{{Harvnb|Beavers|2013|p=481}}</ref>

Born in London, Turing was raised in [[southern England]]. He graduated from [[University of Cambridge|King's College, Cambridge]], and in 1938, earned a doctorate degree from [[Princeton University]]. During [[World War II]], Turing worked for the [[Government Code and Cypher School]] at [[Bletchley Park]], Britain's [[codebreaking]] centre that produced [[Ultra (cryptography)|Ultra]] intelligence. He led [[Hut 8]], the section responsible for German naval cryptanalysis. Turing devised techniques for speeding the breaking of German [[cipher]]s, including improvements to the pre-war Polish [[Bomba (cryptography)|bomba]] method, an [[electromechanical]] machine that could find settings for the [[Enigma machine]]. He played a crucial role in cracking intercepted messages that enabled the [[Allies of World War 2|Allies]] to defeat the [[Axis powers]] in the [[Battle of the Atlantic]] and other engagements.<ref name="bbc-copeland">{{cite news|last=Copeland|first=Jack|author-link=Jack Copeland|date=18 June 2012|title=Alan Turing: The codebreaker who saved 'millions of lives'|publisher=BBC News Technology|url=https://www.bbc.com/news/technology-18419691|url-status=live|access-date=26 October 2014|archive-url=https://web.archive.org/web/20141011045451/http://www.bbc.com/news/technology-18419691|archive-date=11 October 2014}}</ref><ref>A number of sources state that Winston Churchill said that Turing made the single biggest contribution to Allied victory in the war against Nazi Germany. Whilst it may be a defensible claim, both the [[Churchill Centre]] and Turing's biographer [[Andrew Hodges]] have stated they know of no documentary evidence to support it, nor the date or context in which Churchill supposedly made it, and the Churchill Centre lists it among their Churchill 'Myths', see {{cite news |last=Schilling |first=Jonathan |date=8 January 2015 |title=Myths > Churchill Said Turing Made the Single Biggest Contribution to Allied Victory |newspaper=International Churchill Society |url=http://www.winstonchurchill.org/resources/myths/churchill-said-turing-made-the-single-biggest-contribution-to-allied-victory |url-status= |archive-url=https://web.archive.org/web/20150217170510/http://www.winstonchurchill.org/resources/myths/churchill-said-turing-made-the-single-biggest-contribution-to-allied-victory |archive-date=17 February 2015 |access-date=9 January 2015 |publisher=The Churchill Centre }} and {{cite web |last=Hodges |first=Andrew |author-link=Andrew Hodges |title=Part 4: The Relay Race |url=http://www.turing.org.uk/book/update/part4.html |url-status=live |archive-url=https://web.archive.org/web/20150120190931/http://www.turing.org.uk/book/update/part4.html |archive-date=20 January 2015 |access-date=9 January 2015 |publisher=Update to [[Alan Turing: The Enigma]] }} A [[BBC News]] profile piece that repeated the Churchill claim has subsequently been amended to say there is no evidence for it. See {{cite news |last=Spencer |first=Clare |date=11 September 2009 |title=Profile: Alan Turing |work=BBC News |url=http://news.bbc.co.uk/2/hi/uk_news/8250592.stm |url-status=live |access-date=17 February 2015 |archive-url=https://web.archive.org/web/20171213095303/http://www.bbc.com/news/technology-18419691 |archive-date=13 December 2017 |quote=Update 13 February 2015 }} Official war historian [[Harry Hinsley]] estimated that this work shortened the war in Europe by more than two years but added the caveat that this did not account for the [[Manhattan Project|use of the atomic bomb]] and other eventualities. {{citation |last=Hinsley |first=Harry |title=The Influence of ULTRA in the Second World War |url=http://www.cix.co.uk/~klockstone/hinsley.htm |year=1996 |publisher=Keith Lockstone's home page |author-link=Harry Hinsley |orig-date=1993 |access-date=26 August 2024 |archive-date=15 October 2022 |archive-url=https://web.archive.org/web/20221015210957/https://www.cix.co.uk/~klockstone/hinsley.htm |url-status=live }} Transcript of a lecture given on Tuesday 19 October 1993 at Cambridge University</ref>

After the war, Turing worked at the [[National Physical Laboratory (United Kingdom)|National Physical Laboratory]], where he designed the [[Automatic Computing Engine]], one of the first designs for a stored-program computer. In 1948, Turing joined [[Max Newman]]'s [[Computing Machine Laboratory]] at the [[University of Manchester]], where he contributed to the development of early [[Manchester computers]]<ref>{{Harvnb|Leavitt|2007|pp=231–233}}</ref> and became interested in [[mathematical biology]]. Turing wrote on the chemical basis of [[morphogenesis]]<ref name="Milinkovitch">{{cite journal |last1=Milinkovitch |first1=Michel C. |last2=Jahanbakhsh |first2=Ebrahim |last3=Zakany |first3=Szabolcs |title=The Unreasonable Effectiveness of Reaction Diffusion in Vertebrate Skin Color Patterning |journal=Annual Review of Cell and Developmental Biology |date=16 October 2023 |volume=39 |issue=1 |pages=145–174 |doi=10.1146/annurev-cellbio-120319-024414 |language=en |issn=1081-0706|doi-access=free |pmid=37843926 }}</ref><ref name="googlescholar" /> and predicted [[Chemical oscillator|oscillating chemical reactions]] such as the [[Belousov–Zhabotinsky reaction]], first observed in the 1960s. Despite these accomplishments, he was never fully recognised during his lifetime because much of his work was covered by the [[Official Secrets Act 1939|Official Secrets Act]].<ref>{{Cite book |last=Olinick |first=Michael |year=2021 |title=Simply Turing |location=United States |publisher=Simply Charly |chapter=Chapter 15}}</ref>

In 1952, Turing was prosecuted for [[Gross indecency|homosexual acts]]. He accepted hormone treatment, a procedure commonly referred to as [[chemical castration]], as an alternative to prison. Turing died on 7 June 1954, aged 41, from [[cyanide poisoning]]. An inquest determined [[List of LGBT-related suicides|his death as suicide]], but the evidence is also consistent with accidental poisoning.<ref name = "Copeland" /> 
Following a campaign in 2009, British prime minister [[Gordon Brown]] made an [[#Government apology and pardon|official public apology]] for "the appalling way [Turing] was treated". [[Queen Elizabeth II]] granted a [[Royal prerogative of mercy|pardon]] in 2013. The term "[[Alan Turing law]]" is used informally to refer to a 2017 law in the UK that retroactively pardoned men cautioned or convicted under historical legislation that outlawed homosexual acts.<ref name="BBC-pardon">{{cite news |url=https://www.bbc.com/news/uk-37711518 |title='Alan Turing law': Thousands of gay men to be pardoned |date=20 October 2016 |access-date=20 October 2016 |work=BBC News |archive-url=https://web.archive.org/web/20161020125029/http://www.bbc.com/news/uk-37711518 |archive-date=20 October 2016 |url-status=live }}</ref>

Turing left an [[Legacy of Alan Turing|extensive legacy]] in mathematics and computing which has become widely recognised with statues and [[List of things named after Alan Turing|many things named after him]], including an [[Turing Award|annual award]] for computing innovation. His portrait appears on the [[Bank of England £50 note]], first released on 23 June 2021 to coincide with his birthday. The audience vote in a [[Icons: The Greatest Person of the 20th Century|2019 BBC series]] named Turing the greatest person of the 20th century.
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==Early life and education==

===Family===
[[File:Alan Turing (5025990183).jpg|thumb|right|upright|[[English Heritage]] [[blue plaque]] in [[Maida Vale]], London marking Turing's birthplace in 1912]]
Turing was born in [[Maida Vale]], London, while his father, Julius Mathison Turing, was on leave from his position with the [[Indian Civil Service]] (ICS) of the [[British Raj|British Raj government]] at [[Chatrapur]], then in the [[Madras Presidency]] and presently in [[Odisha]] state, in [[India]].<ref name = "Hodges1983P5">{{Harvnb|Hodges|1983|p=5}}</ref><ref>{{cite web |url=http://www.turing.org.uk/turing/scrapbook/early.html |title=The Alan Turing Internet Scrapbook |publisher=[[Alan Turing: The Enigma]] |access-date=2 January 2012 |archive-url=https://web.archive.org/web/20120614051614/http://www.turing.org.uk/turing/scrapbook/early.html |archive-date=14 June 2012 |url-status=live }}</ref> Turing's father was the son of a clergyman, the Rev.&nbsp;John Robert Turing, from a Scottish family of merchants that had been based in the Netherlands and included a [[baronet]]. Turing's mother, Julius's wife, was Ethel Sara Turing ({{nee|Stoney}}), daughter of Edward Waller Stoney, chief engineer of the [[Madras and Southern Mahratta Railway|Madras Railways]]. The Stoneys were a [[Protestantism in Ireland|Protestant]] [[Anglo-Irish people|Anglo-Irish]] [[gentry]] family from both [[County Tipperary]] and [[County Longford]], while Ethel herself had spent much of her childhood in [[County Clare]].<ref>{{Cite news |first=Phil |last=Maguire |title=An Irishman's Diary |page=5 |newspaper=[[The Irish Times]] |date=23 June 2012}}</ref> Julius and Ethel married on 1 October 1907 at the Church of Ireland [[St Bartholomew's Church, Dublin|St. Bartholomew's Church]] on [[Clyde Road]] in [[Ballsbridge]], [[Dublin]].<ref>Irish Marriages 1845–1958 / Dublin South, Dublin, Ireland / Group Registration ID 1990366, SR District/Reg Area, Dublin South</ref>

Julius's work with the ICS brought the family to British India, where his grandfather had been a general in the [[Bengal Army]]. However, both Julius and Ethel wanted their children to be brought up in Britain, so they moved to [[Maida Vale]],<ref name="englishheritaget">{{cite web|url=http://www.english-heritage.org.uk/server/show/nav.001002006005/chooseLetter/T |archive-url=https://web.archive.org/web/20090903150218/http://www.english-heritage.org.uk/server/show/nav.001002006005/chooseLetter/T |archive-date=3 September 2009 |title=London Blue Plaques |access-date=10 February 2007 |work=English Heritage |url-status=live}}</ref> London, where Alan Turing was born on 23 June 1912, as recorded by a [[blue plaque]] on the outside of the house of his birth,<ref>{{Cite web |url=http://blogs.nature.com/london/2011/03/16/the-scientific-tourist-in-london-17-alan-turings-birth-place |title=The Scientific Tourist In London: #17 Alan Turing's Birth Place |archive-url=https://web.archive.org/web/20130921054045/http://blogs.nature.com/london/2011/03/16/the-scientific-tourist-in-london-17-alan-turings-birth-place |archive-date=21 September 2013 |website=Nature London Blog}},</ref><ref>{{openplaque|381}}</ref> later the [[Colonnade Hotel (London)|Colonnade Hotel]].<ref name="Hodges1983P5"/><ref name="turingorguk">{{cite web | url=http://www.turing.org.uk/turing/scrapbook/memorial.html | title=The Alan Turing Internet Scrapbook | access-date=26 September 2006 | archive-url=https://wayback.archive-it.org/all/20110720214124/http://www.turing.org.uk/turing/scrapbook/memorial.html | archive-date=20 July 2011 | url-status=live }}</ref> Turing had an elder brother, John Ferrier Turing, father of [[Dermot Turing]], 12th Baronet of the [[Turing baronets]].<ref>{{Cite web |url=https://bletchleypark.org.uk/about-us/bletchley-park-trustees/sir-john-dermot-turing |title=Sir John Dermot Turing |archive-url=https://web.archive.org/web/20171018191443/https://bletchleypark.org.uk/about-us/bletchley-park-trustees/sir-john-dermot-turing |archive-date=18 October 2017 |website=Bletchley Park}}</ref> In 1922, he discovered ''Natural Wonders Every Child Should Know'' by [[Edwin Tenney Brewster]]. He credited it with opening his eyes to science.{{sfn|Hodges|1983|p=16}}

Turing's father's civil service commission was still active during Turing's childhood years, and his parents travelled between [[Hastings]] in the United Kingdom<ref>{{Harvnb|Hodges|1983|p=6}}</ref> and India, leaving their two sons to stay with a retired [[British Army|Army]] couple. At Hastings, Turing stayed at [[Baston Lodge]], Upper Maze Hill, [[St Leonards-on-Sea]], now marked with a blue plaque.<ref name="Hastings & St. Leonards Observer - 29 June 2012 - Plaque unveiled at Turing's home in St Leonards">{{cite news|url=http://www.hastingsobserver.co.uk/news/plaque-unveiled-at-turing-s-home-in-st-leonards-1-4003535|title=Plaque unveiled at Turing's home in St Leonards|date=29 June 2012|work=[[Hastings & St. Leonards Observer]]|access-date=3 July 2017|archive-url=https://web.archive.org/web/20170912121655/http://www.hastingsobserver.co.uk/news/plaque-unveiled-at-turing-s-home-in-st-leonards-1-4003535|archive-date=12 September 2017|url-status=dead}}</ref> The plaque was unveiled on 23 June 2012, the centenary of Turing's birth.<ref name="BBC News - 25 June 2012 - St Leonards plaque marks Alan Turing's early years">{{cite news|url=https://www.bbc.com/news/uk-england-sussex-18580826|title=St Leonards plaque marks Alan Turing's early years|date=25 June 2012|work=[[BBC News]]|access-date=3 July 2017|archive-url=https://web.archive.org/web/20171203074933/http://www.bbc.com/news/uk-england-sussex-18580826|archive-date=3 December 2017|url-status=live}}</ref>

Very early in life, Turing's parents purchased a house in [[Guildford]] in 1927, and Turing lived there during school holidays. The location is also marked with a blue plaque.<ref>{{cite news |url=http://www.guildford-dragon.com/2012/11/29/founder-of-computer-science-alan-turings-guildford-stargazing/ |title=Guildford Dragon NEWS |newspaper=The Guildford Dragon |date=29 November 2012 |access-date=31 October 2013 |archive-url=https://web.archive.org/web/20131019062927/http://www.guildford-dragon.com/2012/11/29/founder-of-computer-science-alan-turings-guildford-stargazing/ |archive-date=19 October 2013 |url-status=live }}</ref>

===School===
[[File:Alan Turing Aged 16.jpg|thumb|Turing at age 16, {{Circa|1928|1929}}]]
Turing's parents enrolled him at St Michael's, a primary school at 20 Charles Road, [[St Leonards-on-Sea]], from the age of six to nine. The headmistress recognised his talent, noting that she "...had clever boys and hardworking boys, but Alan is a genius".<ref>{{Cite book|last=Cawthorne|first=Nigel|url=https://www.worldcat.org/oclc/890938716|title=Alan Turing : the enigma man|date=2014|isbn=978-1-78404-535-7|location=London|publisher=Arcturus Publishing|pages=18|oclc=890938716|access-date=26 August 2024|archive-date=17 November 2021|archive-url=https://web.archive.org/web/20211117213134/https://www.worldcat.org/title/alan-turing-the-enigma-man/oclc/890938716|url-status=live}}</ref>

Between January 1922 and 1926, Turing was educated at Hazelhurst Preparatory School, an independent school in the village of [[Frant]] in Sussex (now [[East Sussex]]).<ref>{{cite web|url=http://oldshirburnian.org.uk/wp-content/uploads/2016/04/TURING-Alan-Mathison.pdf|title=Alan Turing Archive – Sherborne School (ARCHON CODE: GB1949)|author=Alan Mathison|work=Sherborne School, Dorset|date=April 2016|access-date=5 February 2017|archive-url=https://web.archive.org/web/20161226093015/http://oldshirburnian.org.uk/wp-content/uploads/2016/04/TURING-Alan-Mathison.pdf|archive-date=26 December 2016|url-status=live}}</ref> In 1926, at the age of 13, he went on to [[Sherborne School]],<ref>{{Cite web|date=1 September 2016|title=Alan Turing OBE, PhD, FRS (1912–1954)|url=https://oldshirburnian.org.uk/alan-turing/|access-date=10 October 2020|website=The Old Shirburnian Society|language=en-GB|archive-date=4 November 2020|archive-url=https://web.archive.org/web/20201104133822/https://oldshirburnian.org.uk/alan-turing/|url-status=live}}</ref> an independent boarding school in the market town of [[Sherborne]] in Dorset, where he boarded at Westcott House. The first day of term coincided with the [[1926 United Kingdom general strike|1926 General Strike]], in Britain, but Turing was so determined to attend that he rode his bicycle unaccompanied {{convert|60|mi|km}} from [[Southampton]] to Sherborne, stopping overnight at an inn.<ref name=metamagical>{{Cite book|title=Metamagical Themas: Questing for the Essence of Mind and Pattern |page=[https://books.google.com/books?id=o8jzWF7rD6oC&pg=PA484 484]|first=Douglas R. |last=Hofstadter|author-link=Douglas Hofstadter|year=1985 |publisher=Basic Books |isbn=978-0-465-04566-2 |oclc=230812136}}</ref>

Turing's natural inclination towards mathematics and science did not earn him respect from some of the teachers at Sherborne, whose [[definition of education]] placed more emphasis on the [[classics]]. His headmaster wrote to his parents: "I hope he will not fall between two stools. If he is to stay at public school, he must aim at becoming ''educated''. If he is to be solely a ''Scientific Specialist'', he is wasting his time at a public school".<ref>{{Harvnb|Hodges|1983|p=26}}</ref> Despite this, Turing continued to show remarkable ability in the studies he loved, solving advanced problems in 1927 without having studied even elementary [[calculus]]. In 1928, aged 16, Turing encountered [[Albert Einstein]]'s work; not only did he grasp it, but it is possible that he managed to deduce Einstein's questioning of [[Newton's laws of motion]] from a text in which this was never made explicit.<ref>{{Harvnb|Hodges|1983|p=34}}</ref>

===Christopher Morcom===
At Sherborne, Turing formed a significant friendship with fellow pupil Christopher Collan Morcom (13 July 1911 – 13 February 1930),<ref>{{Cite web|url=https://oldshirburnian.org.uk/wp-content/uploads/2015/01/Obituary-for-Christopher-Morcom-The-Shirburnian-March-1930.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://oldshirburnian.org.uk/wp-content/uploads/2015/01/Obituary-for-Christopher-Morcom-The-Shirburnian-March-1930.pdf |archive-date=9 October 2022 |url-status=live|title=''The Shirburnian''}}</ref> who has been described as Turing's first love.<ref>{{cite book |title=The Alyson Almanac: A Treasury of Information for the Gay and Lesbian Community |date=1989 |publisher=Alyson Publications |isbn=978-0-932870-19-3 |page=192 |url=https://books.google.com/books?id=v-8gAQAAMAAJ |language=en |quote=After his first love, Christopher Morcom, died of tuberculosis ... |access-date=26 August 2024 |archive-date=7 November 2023 |archive-url=https://web.archive.org/web/20231107005431/https://books.google.com/books?id=v-8gAQAAMAAJ |url-status=live }}</ref><ref>{{cite book |last1=Hodges |first1=Andrew |title=Alan Turing: The Enigma |date=1992 |publisher=Vintage |isbn=978-0-09-911641-7 |page=35 |url=https://books.google.com/books?id=VWvPIWm75XIC |quote=This was first love, which Alan would himself come to regard as the first of many for others of his own sex. |access-date=26 August 2024 |archive-date=8 September 2023 |archive-url=https://web.archive.org/web/20230908030210/https://books.google.com/books?id=VWvPIWm75XIC |url-status=live }}</ref><ref>{{cite book |title=Tekhnema: Journal of Philosophy and Technology |date=1995 |publisher=American University of Paris |page=57 |url=https://books.google.com/books?id=wkvGAAAAIAAJ |quote=... Turing's first platonic love, Christopher Morcom ...}}</ref> Their relationship provided inspiration in Turing's future endeavours, but it was cut short by Morcom's death, in February 1930, from complications of [[bovine tuberculosis]], contracted after drinking infected cow's milk some years previously.<ref name=NYReviewBooks>{{cite web|author=Caryl, Christian|title=Poor Imitation of Alan Turing|url=http://www.nybooks.com/blogs/nyrblog/2014/dec/19/poor-imitation-alan-turing/|newspaper=[[New York Review of Books]]|date=19 December 2014|access-date=9 January 2015|archive-url=https://web.archive.org/web/20150107010418/http://www.nybooks.com/blogs/nyrblog/2014/dec/19/poor-imitation-alan-turing/|archive-date=7 January 2015|url-status=live}}</ref><ref>{{cite web |first=Rachel |last=Hassall |url=http://oldshirburnian.org.uk/wp-content/uploads/2014/03/The-Sherborne-Formula-Vivat-2012-2013-optimised.pdf |title=The Sherborne Formula: The Making of Alan Turing |archive-url=https://web.archive.org/web/20140415082353/http://oldshirburnian.org.uk/wp-content/uploads/2014/03/The-Sherborne-Formula-Vivat-2012-2013-optimised.pdf |archive-date=15 April 2014 |work=Vivat! |date=2012–2013}}</ref><ref name=teuscher>{{Cite book|editor-last=Teuscher |editor-first=Christof|editor-link=Christof Teuscher |title=Alan Turing: Life and Legacy of a Great Thinker |year=2004 |publisher=[[Springer Science+Business Media|Springer-Verlag]] |isbn=978-3-540-20020-8 |oclc=53434737 }}</ref>

The event caused Turing great sorrow. He coped with his grief by working that much harder on the topics of science and mathematics that he had shared with Morcom. In a letter to Morcom's mother, Frances Isobel Morcom (née Swan), Turing wrote:

{{blockquote|I am sure I could not have found anywhere another companion so brilliant and yet so charming and unconceited. I regarded my interest in my work, and in such things as astronomy (to which he introduced me) as something to be shared with him and I think he felt a little the same about me&nbsp;... I know I must put as much energy if not as much interest into my work as if he were alive, because that is what he would like me to do.<ref>{{Harvnb|Hodges|1983|p=61}}</ref>}}

Turing's relationship with Morcom's mother continued long after Morcom's death, with her sending gifts to Turing, and him sending letters, typically on Morcom's birthday.<ref name=":1">{{cite book |title=Alan Turing: The Enigma |publisher=Princeton University Press |author-link=Andrew Hodges |last=Hodges |first=Andrew |page=[https://archive.org/details/alanturingenigma0000hodg/page/87 87] |year=2012 |isbn=978-0-691-15564-7 |url=https://archive.org/details/alanturingenigma0000hodg|url-access=registration }}</ref> A day before the third anniversary of Morcom's death (13 February 1933), he wrote to Mrs. Morcom:

{{blockquote|I expect you will be thinking of Chris when this reaches you. I shall too, and this letter is just to tell you that I shall be thinking of Chris and of you tomorrow. I am sure that he is as happy now as he was when he was here. Your affectionate Alan.<ref>{{cite book |title=Alan Turing: The Enigma |publisher=Princeton University Press |author-link=Andrew Hodges |last=Hodges |first=Andrew |page=[https://archive.org/details/alanturingenigma0000hodg/page/90 90] |year=2012 |isbn=978-0-691-15564-7 |url=https://archive.org/details/alanturingenigma0000hodg|url-access=registration }}</ref>}}

Some have speculated that Morcom's death was the cause of Turing's [[atheism]] and [[materialism]].<ref>{{Cite news |first=Paul |last=Gray |url=http://www.time.com/time/magazine/article/0,9171,990624,00.html |title=Alan Turing |archive-url=https://web.archive.org/web/20110119181237/http://www.time.com/time/magazine/article/0,9171,990624,00.html |archive-date=19 January 2011 |work=Time Magazine's Most Important People of the Century |page=2}}</ref> Apparently, at this point in his life he still believed in such concepts as a spirit, independent of the body and surviving death. In a later letter, also written to Morcom's mother, Turing wrote:

{{blockquote|Personally, I believe that spirit is really eternally connected with matter but certainly not by the same kind of body&nbsp;... as regards the actual connection between spirit and body I consider that the body can hold on to a 'spirit', whilst the body is alive and awake the two are firmly connected. When the body is asleep I cannot guess what happens but when the body dies, the 'mechanism' of the body, holding the spirit is gone and the spirit finds a new body sooner or later, perhaps immediately.<ref>{{Harvnb|Hodges|1983|pp=82–83}}</ref><ref>{{Cite web|url=https://oldshirburnian.org.uk/alan-turing-and-the-nature-of-spirit/|title=Alan Turing and the 'Nature of Spirit'|website=oldshirburnian.org.uk|date=15 August 2020|access-date=26 August 2024|archive-date=20 December 2017|archive-url=https://web.archive.org/web/20171220185715/http://oldshirburnian.org.uk/alan-turing-and-the-nature-of-spirit/|url-status=live}}</ref>}}

===University and work on computability===
[[File:Alan Turing az 1930-as években.jpg|thumb|Turing in the 1930s]]
After graduating from Sherborne, Turing applied for several Cambridge colleges scholarships, including [[Trinity College, Cambridge|Trinity]] and [[King's College, Cambridge|King's]], eventually earning an £80 per annum scholarship (equivalent to about £4,300 as of 2023) to study at the latter.{{sfn|Hodges|1983|p=74–5}}<ref>{{cite web | url=https://www.bankofengland.co.uk/monetary-policy/inflation/inflation-calculator | title=Inflation calculator | access-date=26 August 2024 | archive-date=5 October 2018 | archive-url=https://web.archive.org/web/20181005211045/https://www.bankofengland.co.uk/monetary-policy/inflation/inflation-calculator | url-status=live }}</ref> There, Turing studied the undergraduate course in Schedule B <ref>(Schedule B was a three-year scheme consisting of Parts I and II, of the [[Mathematical Tripos]], with extra courses at the end of the third year, as Part III only emerged as a separate degree in 1934</ref> from February 1931 to November 1934 at [[King's College, Cambridge]], where he was awarded first-class honours in mathematics. His dissertation, ''On the Gaussian error function'', written during his senior year and delivered in November 1934 (with a deadline date of 6 December) proved a version of the [[central limit theorem]]. It was finally accepted on 16 March 1935. By spring of that same year, Turing started his master's course ([[Part III of the Mathematical Tripos|Part III]])—which he completed in 1937—and, at the same time, he published his first paper, a one-page article called ''Equivalence of left and right almost periodicity'' (sent on 23 April), featured in the tenth volume of the ''[[London Mathematical Society|Journal of the London Mathematical Society]]''.<ref>{{cite web | url=https://turingarchive.kings.cam.ac.uk/publications-lectures-and-talks-amtb/amt-b-10 | title=AMT-B-10 &#124; the Turing Digital Archive }}</ref> Later that year, Turing was elected a [[Fellow]] of King's College on the strength of his dissertation<ref>{{Cite journal |last=Aldrich |first=John |date=December 2009 |title=England and Continental Probability in the Inter-War Years |journal=Electronic Journ@l for History of Probability and Statistics |volume=5 |number=2 |url=https://www.jehps.net/Decembre2009/Aldrich.pdf |pages=7–11}}</ref> where he served as a [[lecturer]].<ref name=lecturer>{{cite web|first=Alan|last=Turing|year=1939|url=https://archivesearch.lib.cam.ac.uk/repositories/7/archival_objects/272543|website=cam.ac.uk|title=Letter From Alan Turing to his mother, Sara Turing, 1939-01-23|quote=“My lectures are going off rather well. There are 14 people coming to them at present. No doubt the attendance will drop off as the term advances.”}}</ref> However, and, unknown to Turing, this version of the theorem he proved in his paper, had already been proven, in 1922, by [[Jarl Waldemar Lindeberg]]. Despite this, the committee found Turing's methods original and so regarded the work worthy of consideration for the fellowship. [[Abram Besicovitch]]'s report for the committee went so far as to say that if Turing's work had been published before Lindeberg's, it would have been "an important event in the mathematical literature of that year".<ref>{{cite book |last=Turing |first=Dermot |author-link=Dermot Turing |title=[[Prof: Alan Turing Decoded]] |year=2015 |publisher=[[The History Press]] |isbn=9781841656434 |page= 69}}</ref>{{sfn|Hodges|1983|p=113}}<ref>{{cite journal|title=Alan Turing and the Central Limit Theorem |first=S. L. |last=Zabell |pages=483–494 |journal=The American Mathematical Monthly |volume=102 |year=1995 |number=6 |doi=10.1080/00029890.1995.12004608}}</ref>

Between the springs of 1935 and 1936, at the same time as [[Alonzo Church]], Turing worked on the decidability of problems, starting from [[Gödel's incompleteness theorems]]. In mid-April 1936, Turing sent Max Newman the first draft typescript of his investigations. That same month, Church published his ''An Unsolvable Problem of Elementary Number Theory'', with similar conclusions to Turing's then-yet unpublished work. Finally, on 28 May of that year, he finished and delivered his 36-page paper for publication called "[[On Computable Numbers, with an Application to the Entscheidungsproblem]]".<ref name=computable>{{Cite journal | last = Turing | first = A. M. | publication-date = 1937 | title = On Computable Numbers, with an Application to the Entscheidungsproblem: A correction | periodical = Proceedings of the London Mathematical Society | series = 2 | volume = 43 | pages = 544–46 | doi = 10.1112/plms/s2-43.6.544 | year = 1938 | issue = 1 }}</ref><ref>{{Harvnb|Turing|1937}}</ref> It was published in the ''Proceedings of the London Mathematical Society'' journal in two parts, the first on 30 November and the second on 23 December.<ref>{{cite book |url=https://books.google.com/books?id=MlsJuSj2OkEC&pg=PA211 |page=211 |title=Computability: Turing, Gödel, Church, and Beyond |author1=B. Jack Copeland |author2=Carl J. Posy |author3=Oron Shagrir |publisher=MIT Press |year=2013|isbn=978-0-262-01899-9 }}</ref> In this paper, Turing reformulated [[Kurt Gödel]]'s 1931 results on the limits of proof and computation, replacing Gödel's universal arithmetic-based formal language with the formal and simple hypothetical devices that became known as [[Turing machine]]s. The ''[[Entscheidungsproblem]]'' (decision problem) was originally posed by German mathematician [[David Hilbert]] in 1928. Turing proved that his "universal computing machine" would be capable of performing any conceivable mathematical computation if it were representable as an [[algorithm]]. He went on to prove that there was no solution to the ''decision problem'' by first showing that the [[halting problem]] for Turing machines is [[Decision problem|undecidable]]: it is not possible to decide algorithmically whether a Turing machine will ever halt. This paper has been called "easily the most influential math paper in history".<ref>{{cite book |page=15 |title=Mathematics and Computation |author=Avi Wigderson |publisher=Princeton University Press |year=2019|isbn=978-0-691-18913-0 }}</ref>

[[File:20130808 Kings College Front Court Fountain Crop 03.jpg|thumb|right|[[King's College, Cambridge]], where Turing was an undergraduate in 1931 and became a Fellow in 1935. The computer room is named after him.]]
Although [[Turing's proof]] was published shortly after Church's equivalent proof using his [[lambda calculus]],<ref>{{Harvnb|Church|1936}}</ref> Turing's approach is considerably more accessible and intuitive than Church's.<ref>{{cite web|last1=Grime|first1=James|title=What Did Turing Do for Us?|url=https://nrich.maths.org/8050|website=[[NRICH]]|publisher=[[University of Cambridge]]|access-date=28 February 2016|date=February 2012|archive-url=https://web.archive.org/web/20160304175703/http://nrich.maths.org/8050|archive-date=4 March 2016|url-status=live}}</ref> It also included a notion of a 'Universal Machine' (now known as a [[universal Turing machine]]), with the idea that such a machine could perform the tasks of any other computation machine (as indeed could Church's lambda calculus). According to the [[Church–Turing thesis]], Turing machines and the lambda calculus are capable of computing anything that is computable. [[John von Neumann]] acknowledged that the central concept of the modern computer was due to Turing's paper.<ref>"von Neumann&nbsp;... firmly emphasised to me, and to others I am sure, that the fundamental conception is owing to Turing—insofar as not anticipated by Babbage, Lovelace and others." Letter by [[Stanley Frankel]] to [[Brian Randell]], 1972, quoted in [[Jack Copeland]] (2004) ''The Essential Turing'', p.&nbsp;22.</ref> To this day, Turing machines are a central object of study in [[theory of computation]].<ref>{{Citation |last=De Mol |first=Liesbeth |title=Turing Machines |date=2021 |url=https://plato.stanford.edu/archives/win2021/entries/turing-machine/ |encyclopedia=The Stanford Encyclopedia of Philosophy |editor-last=Zalta |editor-first=Edward N. |access-date=12 July 2023 |edition=Winter 2021 |publisher=Metaphysics Research Lab, Stanford University |archive-url= https://web.archive.org/web/20221016224306/https://plato.stanford.edu/archives/win2021/entries/turing-machine/ |archive-date= 16 October 2022 |url-status=live }}</ref>

From September 1936 to July 1938, Turing spent most of his time studying under Church at [[Princeton University]],<ref name="bowen19" /> in the second year as a [[Jane Eliza Procter Fellowship|Jane Eliza Procter Visiting Fellow]]. In addition to his purely mathematical work, he studied cryptology and also built three of four stages of an electro-mechanical [[binary multiplier]].<ref>{{Harvnb|Hodges|1983|p=138}}</ref> In June 1938, he obtained his PhD from the [[Princeton University Department of Mathematics|Department of Mathematics]] at Princeton;<ref>{{Cite journal
| last1 = Turing | first1 = A.M.
| author-link = Alan Turing
| title = Systems of Logic Based on Ordinals
| doi = 10.1112/plms/s2-45.1.161
| journal = Proceedings of the London Mathematical Society
| pages = 161–228
| year = 1939
| volume=s2-45
| issue = 1
| hdl = 21.11116/0000-0001-91CE-3
| hdl-access = free
}}</ref> his dissertation, ''[[Systems of Logic Based on Ordinals]]'',<ref name="turingphd">{{cite thesis |degree=PhD |first=Alan|last=Turing |title=Systems of Logic Based on Ordinals|journal=Proceedings of the London Mathematical Society |publisher=Princeton University |year=1938 |volume=s2-45 |issue=1 |doi=10.1112/plms/s2-45.1.161|author-link=Alan Turing|id={{ProQuest|301792588}}|hdl=21.11116/0000-0001-91CE-3|hdl-access=free}}</ref><ref>{{cite web | last = Turing | first = A.M. | author-link = Alan Turing | title = Systems of Logic Based on Ordinals | year = 1938 | url = https://webspace.princeton.edu/users/jedwards/Turing%20Centennial%202012/Mudd%20Archive%20files/12285_AC100_Turing_1938.pdf | access-date = 4 February 2012 | archive-url = https://web.archive.org/web/20121023103503/https://webspace.princeton.edu/users/jedwards/Turing%20Centennial%202012/Mudd%20Archive%20files/12285_AC100_Turing_1938.pdf | archive-date = 23 October 2012 | url-status = dead }}</ref> introduced the concept of [[ordinal logic]] and the notion of [[Turing reduction|relative computing]], in which Turing machines are augmented with so-called [[oracle machine|oracles]], allowing the study of problems that cannot be solved by Turing machines. John von Neumann wanted to hire him as his [[Postdoctoral researcher|postdoctoral assistant]], but he went back to the United Kingdom.<ref>''John Von Neumann: The Scientific Genius Who Pioneered the Modern Computer, Game Theory, Nuclear Deterrence, and Much More'', Norman MacRae, 1999, American Mathematical Society, Chapter 8</ref>

==Career and research==
When Turing returned to Cambridge, he attended lectures given in 1939 by [[Ludwig Wittgenstein]] about the [[foundations of mathematics]].<ref>{{Harvnb|Hodges|1983|p=152}}</ref> The lectures have been reconstructed verbatim, including interjections from Turing and other students, from students' notes.<ref>{{Cite book |editor-first=Cora |editor-last=Diamond |editor-link=Cora Diamond |title=Wittgenstein's Lectures on the Foundations of Mathematics |publisher=University of Chicago Press |year=1976}}</ref> Turing and Wittgenstein argued and disagreed, with Turing defending [[Philosophy of mathematics#Formalism|formalism]] and Wittgenstein propounding his view that mathematics does not discover any absolute truths, but rather invents them.<ref>{{Harvnb|Hodges|1983|pp=153–154}}</ref>

===Cryptanalysis===
During the Second World War, Turing was a leading participant in the breaking of German ciphers at [[Bletchley Park]]. The historian and wartime codebreaker [[Asa Briggs]] has said, "You needed exceptional talent, you needed genius at Bletchley and Turing's was that genius."<ref>{{Cite AV media | last = Briggs | first = Asa | author-link = Asa Briggs | title = Britain's Greatest Codebreaker | type = TV broadcast | publisher = [[Channel 4|UK Channel 4]] | date = 21 November 2011}}</ref>

From September 1938, Turing worked part-time with the [[Government Code and Cypher School]] (GC&CS), the British codebreaking organisation. He concentrated on [[cryptanalysis of the Enigma|cryptanalysis of the Enigma cipher machine]] used by [[Nazi Germany]], together with [[Dilly Knox]], a senior GC&CS codebreaker.<ref>{{Cite book | author-link = Jack Copeland | last = Copeland | first = Jack | chapter = Colossus and the Dawning of the Computer Age | page = 352 | title = Action This Day | publisher = Bantam | date = 2001 | isbn = 978-0-593-04910-5 | editor1-first = Michael | editor1-last = Smith | editor2-first = Ralph | editor2-last = Erskine }}</ref> Soon after the July 1939 meeting near [[Warsaw]] at which the [[Polish Cipher Bureau]] gave the British and French details of the wiring of [[Enigma rotor details|Enigma machine's rotors]] and their method of decrypting [[Enigma machine]]'s messages, Turing and Knox developed a broader solution.<ref>{{Harvnb|Copeland|2004a|p=217}}</ref> The Polish method relied on an insecure [[Cryptanalysis#Indicator|indicator]] procedure that the Germans were likely to change, which they in fact did in May 1940. Turing's approach was more general, using [[Cryptanalysis of the Enigma#Crib-based decryption|crib-based decryption]] for which he produced the functional specification of the [[bombe]] (an improvement on the Polish [[Bomba (cryptography)|Bomba]]).<ref>{{cite news |last=Clark |first=Liat |url=https://www.wired.co.uk/news/archive/2012-06/18/turing-contributions?page=all |title=Turing's achievements: codebreaking, AI and the birth of computer science (Wired UK) |magazine=Wired |date=18 June 2012 |access-date=31 October 2013 |archive-url=https://web.archive.org/web/20131102122933/http://www.wired.co.uk/news/archive/2012-06/18/turing-contributions?page=all |archive-date=2 November 2013 |url-status=live }}</ref>

[[File:Turing flat.jpg|thumb|right|Two cottages in the stable yard at [[Bletchley Park]]. Turing worked here in 1939 and 1940, before moving to [[Hut 8]].]]

On 4 September 1939, the day after the UK declared war on Germany, Turing reported to Bletchley Park, the wartime station of GC&CS.<ref name=Copeland2006p378>Copeland, 2006 p.&nbsp;378.</ref> Like all others who came to Bletchley, he was required to sign the [[Official Secrets Act 1939|Official Secrets Act]], in which he agreed not to disclose anything about his work at Bletchley, with severe legal penalties for violating the Act.<ref name="Collins">{{cite web |last=Collins |first=Jeremy |title=Alan Turing and the Hidden Heroes of Bletchley Park: A Conversation with Sir John Dermot Turing |date=24 June 2020 |location=New Orleans |publisher=The National WWII Museum |url=https://www.nationalww2museum.org/war/articles/alan-turing-betchley-park |access-date=24 August 2021 |archive-date=2 December 2021 |archive-url=https://web.archive.org/web/20211202101721/https://www.nationalww2museum.org/war/articles/alan-turing-betchley-park |url-status=live }}</ref>

Specifying the bombe was the first of five major cryptanalytical advances that Turing made during the war. The others were: deducing the indicator procedure used by the German navy; developing a statistical procedure dubbed ''[[Banburismus]]'' for making much more efficient use of the bombes; developing a procedure dubbed ''[[Turingery]]'' for working out the cam settings of the wheels of the [[Lorenz SZ 40/42]] (''Tunny'') cipher machine and, towards the end of the war, the development of a portable [[secure voice]] scrambler at [[Her Majesty's Government Communications Centre|Hanslope Park]] that was codenamed Delilah.<ref>{{Cite web |title=How Alan Turing Cracked The Enigma Code |url=https://www.iwm.org.uk/history/how-alan-turing-cracked-the-enigma-code |access-date=12 July 2023 |website=Imperial War Museums |language=en |archive-date=24 January 2022 |archive-url=https://web.archive.org/web/20220124140731/https://www.iwm.org.uk/history/how-alan-turing-cracked-the-enigma-code |url-status=live }}</ref><ref>{{Cite journal |last1=Turing |first1=Alan M. |last2=Bayley |first2=D. |date=2012 |title=Report on Speech Secrecy System DELILAH, a Technical Description Compiled by A. M. Turing and Lieutenant D. Bayley REME, 1945–1946 |url=http://www.tandfonline.com/doi/abs/10.1080/01611194.2012.713803 |journal=Cryptologia |language=en |volume=36 |issue=4 |pages=295–340 |doi=10.1080/01611194.2012.713803 |s2cid=205488183 |issn=0161-1194 |access-date=26 August 2024 |archive-date=12 July 2023 |archive-url=https://web.archive.org/web/20230712092022/https://www.tandfonline.com/doi/abs/10.1080/01611194.2012.713803 |url-status=live }}</ref>

By using statistical techniques to optimise the trial of different possibilities in the code breaking process, Turing made an innovative contribution to the subject. He wrote two papers discussing mathematical approaches, titled ''The Applications of Probability to Cryptography''<ref>{{cite web | last = Turing | first = Alan | year = c. 1941 | title = The Applications of Probability to Cryptography | id = The National Archives (United Kingdom): HW 25/37 | url = http://discovery.nationalarchives.gov.uk/details/r/C11510465 | access-date = 25 March 2015 | archive-url = https://web.archive.org/web/20150407234050/http://discovery.nationalarchives.gov.uk/details/r/C11510465 | archive-date = 7 April 2015 | url-status = live }}</ref> and ''Paper on Statistics of Repetitions'',<ref>{{cite web | last = Turing | first = Alan | year = c. 1941 | title = Paper on Statistics of Repetitions | id = The National Archives (United Kingdom): HW 25/38 | url = http://discovery.nationalarchives.gov.uk/details/r/C11510466 | access-date = 25 March 2015 | archive-url = https://web.archive.org/web/20150408013845/http://discovery.nationalarchives.gov.uk/details/r/C11510466 | archive-date = 8 April 2015 | url-status = live }}</ref> which were of such value to GC&CS and its successor [[GCHQ]] that they were not released to the [[The National Archives (United Kingdom)|UK National Archives]] until April 2012, shortly before the centenary of his birth. A GCHQ mathematician, "who identified himself only as Richard," said at the time that the fact that the contents had been restricted under the Official Secrets Act for some 70 years demonstrated their importance, and their relevance to post-war cryptanalysis:<ref name=bbcrichard>{{cite news |last=Vallance |first=Chris |title=Alan Turing papers on code breaking released by GCHQ |url=https://www.bbc.co.uk/news/technology-17771962 |access-date=20 April 2012 |work=BBC News |date=19 April 2012 |archive-url=https://web.archive.org/web/20121004192554/http://www.bbc.co.uk/news/technology-17771962 |archive-date=4 October 2012 |url-status=live }}</ref>

{{blockquote|text=[He] said the fact that the contents had been restricted "shows what a tremendous importance it has in the foundations of our subject". ... The papers detailed using "mathematical analysis to try and determine which are the more likely settings so that they can be tried as quickly as possible". ... Richard said that GCHQ had now "squeezed the juice" out of the two papers and was "happy for them to be released into the public domain".}}

Turing had a reputation for eccentricity at Bletchley Park. He was known to his colleagues as "Prof" and his treatise on Enigma was known as the "Prof's Book".<ref>{{Harvnb|Hodges|1983|p=208}}</ref><ref>{{cite book |title=The Prof's Book: Turing's Treatise on the Enigma |first=Alan M. |last=Turing |year=1940 |url=https://archive.org/details/hw-25-3/ |url-access=registration |quote=In late 1940 Alan Turing wrote a report describing the methods he and his colleagues at Bletchley Park had used to break into the German Enigma cipher systems. At Bletchley it was known as 'the Prof's Book.' A copy of this handbook was at last released from secrecy by the American National Security Agency in April 1996, under the title ''Turing's Treatise on the Enigma''. Subsequently, a much better original copy was released by the (British) National Archives, box HW 25/3. This also revealed a title which had been lost in the American copy: ''Mathematical theory of ENIGMA machine''. (Though, oddly, the report does not actually have any mathematical theory.)}}</ref> According to historian [[Ronald Lewin]], [[I.J. Good|Jack Good]], a cryptanalyst who worked with Turing, said of his colleague:

{{blockquote|In the first week of June each year he would get a bad attack of hay fever, and he would cycle to the office wearing a service gas mask to keep the pollen off. His bicycle had a fault: the chain would come off at regular intervals. Instead of having it mended he would count the number of times the pedals went round and would get off the bicycle in time to adjust the chain by hand. Another of his eccentricities is that he chained his mug to the radiator pipes to prevent it being stolen.<ref>{{Harvnb|Lewin|1978|p=57}}</ref>}}

[[Peter Hilton]] recounted his experience working with Turing in [[Hut 8]] in his "Reminiscences of Bletchley Park" from ''A Century of Mathematics in America:''<ref>{{Cite web|url=http://www.ams.org/publicoutreach/math-history/hmath1-hilton22.pdf|title=A Century of Mathematics in America, Part 1, Reminiscences of Bletchley Park|last=Hilton|first=Peter|archive-url=https://web.archive.org/web/20190829112241/http://www.ams.org/publicoutreach/math-history/hmath1-hilton22.pdf|archive-date=29 August 2019|url-status=live}}</ref>

{{blockquote| It is a rare experience to meet an authentic genius. Those of us privileged to inhabit the world of scholarship are familiar with the intellectual stimulation furnished by talented colleagues. We can admire the ideas they share with us and are usually able to understand their source; we may even often believe that we ourselves could have created such concepts and originated such thoughts. However, the experience of sharing the intellectual life of a genius is entirely different; one realizes that one is in the presence of an intelligence, a sensibility of such profundity and originality that one is filled with wonder and excitement.
Alan Turing was such a genius, and those, like myself, who had the astonishing and unexpected opportunity, created by the strange exigencies of the Second World War, to be able to count Turing as colleague and friend will never forget that experience, nor can we ever lose its immense benefit to us.|sign=|source=}}

Hilton echoed similar thoughts in the Nova [[PBS]] documentary ''Decoding Nazi Secrets''.<ref>{{Cite web|url=https://www.pbs.org/wgbh/nova/transcripts/2615decoding.html|title=NOVA {{!}} Transcripts {{!}} Decoding Nazi Secrets|last=Hilton|first=Peter|website=[[PBS]]|archive-url=https://web.archive.org/web/20190829112240/https://www.pbs.org/wgbh/nova/transcripts/2615decoding.html|archive-date=29 August 2019|url-status=live}}</ref>

While working at Bletchley, Turing, who was a talented [[Long-distance running|long-distance runner]], occasionally ran the {{convert|40|mi}} to London when he was needed for meetings,<ref>{{Cite book | last = Brown | first = Anthony Cave | author-link = Anthony Cave Brown | title = Bodyguard of Lies: The Extraordinary True Story Behind D-Day | page = 19 | publisher=The Lyons Press | year = 1975 | isbn = 978-1-59921-383-5 | url = https://archive.org/details/bodyguardoflies00brow | url-access = registration}}</ref> and he was capable of world-class marathon standards.<ref>{{cite news|url=https://www.theguardian.com/commentisfree/2010/mar/10/alan-turing-2012-olympics|title=An Olympic honour for Alan Turing|author=Graham-Cumming, John|newspaper=The Guardian|date=10 March 2010|location=London|access-date=10 December 2016|archive-url=https://web.archive.org/web/20161201171628/https://www.theguardian.com/commentisfree/2010/mar/10/alan-turing-2012-olympics|archive-date=1 December 2016|url-status=live}}</ref><ref>{{cite web | first=Pat | last=Butcher | url=http://www.globerunner.org/index.php/09/in-praise-of-great-men/ | title=In Praise of Great Men | publisher=Globe Runner | date=14 September 2009 | access-date=23 June 2012 | archive-url=https://web.archive.org/web/20130818145759/http://www.globerunner.org/index.php/09/in-praise-of-great-men/ | archive-date=18 August 2013 | url-status=live }}</ref> Turing tried out for the [[Great Britain at the 1948 Summer Olympics|1948 British Olympic team]], but he was hampered by an injury. His tryout time for the marathon was only 11 minutes slower than British silver medallist [[Tom Richards (athlete)|Thomas Richards]]' Olympic race time of 2 hours 35 minutes. He was Walton Athletic Club's best runner, a fact discovered when he passed the group while running alone.<ref>{{cite web | last1 = Hodges | first1 = Andrew | author-link = Andrew Hodges | title = Alan Turing: a short biography | url = http://www.turing.org.uk/bio/part6.html | publisher = Alan Turing: The Enigma | access-date = 12 June 2014 | archive-url = https://web.archive.org/web/20130914091359/http://www.turing.org.uk/bio/part6.html | archive-date = 14 September 2013 | url-status = live }}</ref><ref>{{cite news | last1 = Graham-Cumming | first1 = John | author-link = John Graham-Cumming | title = Alan Turing: a short biography | url = https://www.theguardian.com/commentisfree/2010/mar/10/alan-turing-2012-olympics | newspaper = The Guardian | date = 10 March 2010 | access-date = 12 June 2014 | archive-url = https://web.archive.org/web/20141108165218/http://www.theguardian.com/commentisfree/2010/mar/10/alan-turing-2012-olympics | archive-date = 8 November 2014 | url-status = live }}</ref><ref>{{cite web | last1 = Butcher | first1 = Pat | title = Turing as a runner | url = http://www-groups.dcs.st-and.ac.uk/~history/Extras/Turing_running.html | publisher = The MacTutor History of Mathematics archive | date = December 1999 | access-date = 12 June 2014 | archive-url = https://web.archive.org/web/20141113020916/http://www-groups.dcs.st-and.ac.uk/~history/Extras/Turing_running.html | archive-date = 13 November 2014 | url-status = live }}</ref> When asked why he ran so hard in training he replied:

{{blockquote|I have such a stressful job that the only way I can get it out of my mind is by running hard; it's the only way I can get some release.<ref>{{cite web |url=https://kottke.org/18/04/alan-turing-was-an-excellent-runner |first=Jason |last=Kottke |title=Turing was an excellent runner |website=kottke.org |date=17 April 2018 |access-date=26 August 2024 |archive-date=9 June 2021 |archive-url=https://web.archive.org/web/20210609192748/https://kottke.org/18/04/alan-turing-was-an-excellent-runner |url-status=live }}</ref>}}

Due to the problems of [[counterfactual history]], it is hard to estimate the precise effect Ultra intelligence had on the war.<ref>See for example {{cite book|last=Richelson|first=Jeffery T.|title=A Century of Spies: Intelligence in the Twentieth Century|date=1997|publisher=Oxford University Press|location=New York|page=296|author-link=Jeffrey T. Richelson}} and {{cite book|last=Hartcup|first=Guy|title=The Effect of Science on the Second World War|date=2000|publisher=Macmillan Press|location=Basingstoke, Hampshire|pages=96–99|author-link=Guy Hartcup}}</ref> However, official war historian [[Harry Hinsley]] estimated that this work shortened the war in Europe by more than two years but added the caveat that this did not account for the use of the atomic bomb and other eventualities.<ref name="Hinsley 1996">{{citation | last = Hinsley | first = Harry | author-link = Harry Hinsley | title = The Influence of ULTRA in the Second World War | orig-date = 1993 | year = 1996 | url = http://www.cix.co.uk/~klockstone/hinsley.htm | access-date = 26 August 2024 | archive-date = 15 October 2022 | archive-url = https://web.archive.org/web/20221015210957/https://www.cix.co.uk/~klockstone/hinsley.htm | url-status = live }} Transcript of a lecture given on Tuesday 19 October 1993 at Cambridge University</ref>

At the end of the war, a memo was sent to all those who had worked at Bletchley Park, reminding them that the code of silence dictated by the Official Secrets Act did not end with the war but would continue indefinitely.<ref name="Collins"/> Thus, even though Turing was appointed an [[Order of the British Empire|Officer of the Order of the British Empire]] (OBE) in 1946 by King [[George VI]] for his wartime services, his work remained secret for many years.<ref>{{cite news | title = Alan Turing: Colleagues share their memories | url = https://www.bbc.co.uk/news/technology-18541715 | date = 23 June 2012 | work = BBC News | access-date = 21 June 2018 | archive-url = https://web.archive.org/web/20180707105436/https://www.bbc.co.uk/news/technology-18541715 | archive-date = 7 July 2018 | url-status = live }}</ref><ref name="thegazette.co.uk">{{cite web|url=https://www.thegazette.co.uk/all-notices/content/114|title=This month in history: Alan Turing and the Enigma code|website=thegazette.co.uk|access-date=6 February 2019|archive-url=https://web.archive.org/web/20190626211800/https://www.thegazette.co.uk/all-notices/content/114|archive-date=26 June 2019|url-status=live}}</ref>

===Bombe===
Within weeks of arriving at Bletchley Park,<ref name="Copeland2006p378" /> Turing had specified an electromechanical machine called the [[bombe]], which could break Enigma more effectively than the Polish ''[[bomba (cryptography)|bomba kryptologiczna]]'', from which its name was derived. The bombe, with an enhancement suggested by mathematician [[Gordon Welchman]], became one of the primary tools, and the major automated one, used to attack Enigma-enciphered messages.<ref>{{Cite book |last= Welchman |first= Gordon |author-link= Gordon Welchman |orig-year= 1982 |year= 1997 |title= The Hut Six story: Breaking the Enigma codes |page= 81 |location= Cleobury Mortimer, England |publisher= M&M Baldwin |isbn= 978-0-947712-34-1 }}</ref>

[[File:Bombe-rebuild.jpg|thumbnail|right|A working replica of a [[bombe]] now at [[The National Museum of Computing]] on Bletchley Park]]The bombe searched for possible correct settings used for an Enigma message (i.e., rotor order, rotor settings and plugboard settings) using a suitable ''[[crib (cryptanalysis)|crib]]'': a fragment of probable [[plaintext]]. For each possible setting of the rotors (which had on the order of 10<sup>19</sup> states, or 10<sup>22</sup> states for the four-rotor U-boat variant),<ref>Jack Good in "The Men Who Cracked Enigma", 2003: with his caveat: "if my memory is correct".</ref> the bombe performed a chain of logical deductions based on the crib, implemented [[Electromechanics|electromechanically]].<ref>{{cite web |url=https://www.tnmoc.org/bombe |title=The Turing-Welchman Bombe |website=The National Museum of Computing |access-date=18 March 2021 |archive-date=24 January 2022 |archive-url=https://web.archive.org/web/20220124200142/https://www.tnmoc.org/bombe |url-status=live }}</ref>

The bombe detected when a contradiction had occurred and ruled out that setting, moving on to the next. Most of the possible settings would cause contradictions and be discarded, leaving only a few to be investigated in detail. A contradiction would occur when an enciphered letter would be turned back into the same plaintext letter, which was impossible with the Enigma. The first bombe was installed on 18 March 1940.<ref>{{Harvnb|Oakley|2006|p=40/03B}}</ref>

==== Action This Day ====
{{main|Action This Day (memo)}}

By late 1941, Turing and his fellow cryptanalysts [[Gordon Welchman]], [[Conel Hugh O'Donel Alexander|Hugh Alexander]] and [[Stuart Milner-Barry]] were frustrated. Building on the [[Biuro Szyfrów#Gift to allies|work of the Poles]], they had set up a good working system for decrypting Enigma signals, but their limited staff and bombes meant they could not translate all the signals. In the summer, they had considerable success, and shipping losses had fallen to under 100,000 tons a month; however, they badly needed more resources to keep abreast of German adjustments. They had tried to get more people and fund more bombes through the proper channels, but had failed.<ref name=":0" />

On 28 October they wrote directly to [[Winston Churchill]] explaining their difficulties, with Turing as the first named. They emphasised how small their need was compared with the vast expenditure of men and money by the forces and compared with the level of assistance they could offer to the forces.<ref name=":0">{{Harvnb|Hodges|1983|p=218}}</ref> As [[Andrew Hodges]], biographer of Turing, later wrote, "This letter had an electric effect."<ref name="Hodges 1983 221">{{Harvnb|Hodges|1983|p=221}}</ref> Churchill wrote a memo to [[Hastings Ismay, 1st Baron Ismay|General Ismay]], which read: "ACTION THIS DAY. Make sure they have all they want on extreme priority and report to me that this has been done." On 18 November, the chief of the secret service reported that every possible measure was being taken.<ref name="Hodges 1983 221"/> The cryptographers at Bletchley Park did not know of the Prime Minister's response, but as Milner-Barry recalled, "All that we did notice was that almost from that day the rough ways began miraculously to be made smooth."<ref>Copeland, ''The Essential Turing'', [http://www.maths.ed.ac.uk/~aar/turingletter.pdf pp. 336–337] {{Webarchive|url=https://web.archive.org/web/20150218142127/http://www.maths.ed.ac.uk/~aar/turingletter.pdf |date=18 February 2015 }}.</ref> More than two hundred bombes were in operation by the end of the war.<ref name=codebreaker>{{cite web | last1 = Copeland | first1 = Jack | last2 = Proudfoot | first2 = Diane | author-link = Jack Copeland | title = Alan Turing, Codebreaker and Computer Pioneer | url = http://www.alanturing.net/turing_archive/pages/Reference%20Articles/codebreaker.html | publisher = alanturing.net | date = May 2004 | access-date = 27 July 2007 | archive-url = https://web.archive.org/web/20070709065520/http://www.alanturing.net/turing_archive/pages/Reference%20Articles/codebreaker.html | archive-date = 9 July 2007 | url-status = live }}</ref>

===Hut 8 and the naval Enigma===
[[File:Turing-statue-Bletchley 14.jpg|thumb|upright|Statue of Turing holding an Enigma machine by [[Stephen Kettle]] at Bletchley Park, commissioned by [[Sidney Frank]], built from half a million pieces of Welsh slate<ref>{{cite web |title=Bletchley Park Unveils Statue Commemorating Alan Turing |url=http://www.bletchleypark.org.uk/news/docview.rhtm/454075 |access-date=30 June 2007 |archive-url=https://web.archive.org/web/20070630083823/http://www.bletchleypark.org.uk/news/docview.rhtm/454075 |archive-date=30 June 2007 |url-status=live }}</ref>]]

Turing decided to tackle the particularly difficult problem of cracking the [[Cryptanalysis of the Enigma#German Naval Enigma|German naval use of Enigma]] "because no one else was doing anything about it and I could have it to myself".<ref name=MahonP14>{{Harvnb|Mahon|1945|p=14}}</ref> In December 1939, Turing solved the essential part of the naval [[Enigma machine#Indicator|indicator]] system, which was more complex than the indicator systems used by the other services.<ref name=MahonP14 /><ref>{{Harvnb|Leavitt|2007|pp=184–186}}</ref>

That same night, he also conceived of the idea of ''[[Banburismus]]'', a sequential statistical technique (what [[Abraham Wald]] later called [[sequential analysis]]) to assist in breaking the naval Enigma, "though I was not sure that it would work in practice, and was not, in fact, sure until some days had actually broken".<ref name=MahonP14 /> For this, he invented a measure of weight of evidence that he called the ''[[Ban (unit)|ban]]''. ''Banburismus'' could rule out certain sequences of the Enigma rotors, substantially reducing the time needed to test settings on the bombes.<ref>{{Cite journal|last=Gladwin|first=Lee|date=Fall 1997|title=Alan Turing, Enigma, and the Breaking of German Machine Ciphers in World War II|url=https://www.archives.gov/files/publications/prologue/1997/fall/turing.pdf|journal=Prologue Magazine|volume=Fall 1997|pages=202–217|via=National Archives|access-date=13 April 2019|archive-url=https://web.archive.org/web/20190626211657/https://www.archives.gov/files/publications/prologue/1997/fall/turing.pdf|archive-date=26 June 2019|url-status=live}}</ref> Later this sequential process of accumulating sufficient weight of evidence using decibans (one tenth of a ban) was used in [[cryptanalysis of the Lorenz cipher]].<ref>{{Citation | last1 = Good | first1 = Jack | author-link = I. J. Good | last2 = Michie | first2 = Donald | author2-link = Donald Michie | last3 = Timms | first3 = Geoffrey | title = General Report on Tunny: With Emphasis on Statistical Methods | year = 1945 | id = UK Public Record Office HW 25/4 and HW 25/5 | url = http://www.alanturing.net/turing_archive/archive/t/t15/TR15-018.html | at = Part 3 Organisation: 38 Wheel-breaking from Key, Page 293 | access-date = 13 April 2019 | archive-url = https://web.archive.org/web/20190421091539/http://www.alanturing.net/turing_archive/archive/t/t15/TR15-018.html | archive-date = 21 April 2019 | url-status = live }}</ref>

Turing travelled to the United States in November 1942 and worked with US Navy cryptanalysts on the naval Enigma and bombe construction in Washington.<ref>{{Harvnb|Hodges|1983|pp=242–245}}</ref><ref>{{Cite web |title=Alan Turing's Report from Washington, 1942 |url=https://www.turing.org.uk/sources/washington.html |access-date=12 July 2023 |website=www.turing.org.uk |archive-date=12 July 2023 |archive-url=https://web.archive.org/web/20230712083844/https://www.turing.org.uk/sources/washington.html |url-status=live }}</ref> He also visited their [[United States Naval Computing Machine Laboratory|Computing Machine Laboratory]] in [[Dayton, Ohio]].<ref>{{Cite web |title=Alan Turing's Dayton Report, 1942 |url=https://www.turing.org.uk/sources/dayton123.html |access-date=12 July 2023 |website=www.turing.org.uk}}</ref>

Turing's reaction to the American bombe design was far from enthusiastic:

{{blockquote|text=The American Bombe programme was to produce 336 Bombes, one for each wheel order. I used to smile inwardly at the conception of Bombe hut routine implied by this programme, but thought that no particular purpose would be served by pointing out that we would not really use them in that way.

Their test (of commutators) can hardly be considered conclusive as they were not testing for the bounce with electronic stop finding devices. Nobody seems to be told about rods or offiziers or banburismus unless they are really going to do something about it.<ref>{{Cite journal |last=Turing |first=Alan M. |year=2001 |journal=Cryptologia |volume=25 |issue=1 |pages=1–10 |doi=10.1080/0161-110191889734 |title=Visit to National Cash Register Corporation of Dayton, Ohio |s2cid=14207094 }}</ref>|source=}}

During this trip, he also assisted at [[Bell Labs]] with the development of [[secure speech]] devices.<ref>{{Harvnb|Hodges|1983|pp=245–253}}</ref> He returned to Bletchley Park in March 1943. During his absence, [[Colonel Hugh O'Donel Alexander|Hugh Alexander]] had officially assumed the position of head of Hut 8, although Alexander had been ''de facto'' head for some time (Turing having little interest in the day-to-day running of the section). Turing became a general consultant for cryptanalysis at Bletchley Park.<ref>{{Cite web|url=https://www.marshallfoundation.org/newsroom/marshall-legacy-series/codebreaking/|title=Marshall Legacy Series: Codebreaking – Events|website=marshallfoundation.org|access-date=7 April 2019|archive-url=https://web.archive.org/web/20190407030638/https://www.marshallfoundation.org/newsroom/marshall-legacy-series/codebreaking/|archive-date=7 April 2019|url-status=live}}</ref>

Alexander wrote of Turing's contribution:

{{blockquote|There should be no question in anyone's mind that Turing's work was the biggest factor in Hut 8's success. In the early days, he was the only cryptographer who thought the problem worth tackling and not only was he primarily responsible for the main theoretical work within the Hut, but he also shared with Welchman and Keen the chief credit for the invention of the bombe. It is always difficult to say that anyone is 'absolutely indispensable', but if anyone was indispensable to Hut 8, it was Turing. The pioneer's work always tends to be forgotten when experience and routine later make everything seem easy and many of us in Hut 8 felt that the magnitude of Turing's contribution was never fully realised by the outside world.<ref>{{Harvnb|Alexander|circa 1945|p=42}}</ref>}}

===Turingery===
In July 1942, Turing devised a technique termed ''[[Turingery]]'' (or jokingly ''Turingismus<ref>{{Harvnb|Copeland|2006|p=380}}</ref>'') for use against the [[Lorenz cipher]] messages produced by the Germans' new ''Geheimschreiber'' (secret writer) machine. This was a [[teleprinter]] [[Rotor machine|rotor cipher attachment]] codenamed ''Tunny'' at Bletchley Park. Turingery was a method of ''wheel-breaking'', i.e., a procedure for working out the cam settings of Tunny's wheels.<ref>{{Harvnb|Copeland|2006|p=381}}</ref> He also introduced the Tunny team to [[Tommy Flowers]] who, under the guidance of [[Max Newman]], went on to build the [[Colossus computer]], the world's first programmable digital electronic computer, which replaced a simpler prior machine (the [[Heath Robinson (codebreaking machine)|Heath Robinson]]), and whose superior speed allowed the statistical decryption techniques to be applied usefully to the messages.<ref>{{Harvnb|Copeland|2006|p=72}}</ref> Some have mistakenly said that Turing was a key figure in the design of the Colossus computer. Turingery and the statistical approach of Banburismus undoubtedly fed into the thinking about [[cryptanalysis of the Lorenz cipher]],<ref>{{Harvnb|Gannon|2007|p=230}}</ref><ref>{{Harvnb|Hilton|2006|pp=197–199}}</ref> but he was not directly involved in the Colossus development.<ref>{{Harvnb|Copeland|2006|pp=382, 383}}</ref>

===Delilah===
Following his work at [[Bell Labs]] in the US,<ref>{{Harvnb|Hodges|1983|pp=245–250}}</ref> Turing pursued the idea of electronic enciphering of speech in the telephone system. In the latter part of the war, he moved to work for the Secret Service's Radio Security Service (later [[Her Majesty's Government Communications Centre|HMGCC]]) at [[Hanslope Park]].<ref>{{cite journal| last = Harper| first = John| author-link = John Harper (computer engineer)| title = Delilah Voice Secrecy System| journal = Resurrection: The Journal of the Computer Conservation Society| issue = 101| pages = 8–9| publisher = The Computer Conservation Society| date = Spring 2023| url = https://www.computerconservationsociety.org/resurrection/res101.htm#d| access-date = 28 June 2023}}</ref><ref>{{cite journal| last = Harper| first = John| author-link = John Harper (computer engineer)| title = Delilah Voice Secrecy System [part 2]: The Design, Development and Commissioning of Delilah in 1943 – 1945| journal = Resurrection: The Journal of the Computer Conservation Society| issue = 102| pages = 16–19| publisher = The Computer Conservation Society| date = Summer 2023| url = https://www.computerconservationsociety.org/resurrection/res102.htm#c| access-date = 28 June 2023| archive-date = 3 July 2023| archive-url = https://web.archive.org/web/20230703233634/https://www.computerconservationsociety.org/resurrection/res102.htm#c| url-status = live}}</ref> At the park, he further developed his knowledge of electronics with the assistance of [[Royal Electrical and Mechanical Engineers|REME]] officer Donald Bayley. Together they undertook the design and construction of a portable [[secure voice]] communications machine codenamed ''[[Delilah (voice encryption)|Delilah]]''.<ref>{{Harvnb|Hodges|1983|p=273}}</ref> The machine was intended for different applications, but it lacked the capability for use with long-distance radio transmissions. In any case, Delilah was completed too late to be used during the war. Though the system worked fully, with Turing demonstrating it to officials by encrypting and decrypting a recording of a [[Winston Churchill]] speech, Delilah was not adopted for use.<ref>{{Harvnb|Hodges|1983|p=346}}</ref> Turing also consulted with Bell Labs on the development of [[SIGSALY]], a secure voice system that was used in the later years of the war.

===Early computers and the Turing test===
[[File:Alan Turing 78 High Street Hampton blue plaque.jpg|thumb|Plaque, 78 High Street, [[Hampton, London|Hampton]]]]
Between 1945 and 1947, Turing lived in [[Hampton, London|Hampton]], London,<ref>{{openplaque|1619}}</ref> while he worked on the design of the [[ACE (computer)|ACE]] (Automatic Computing Engine) at the [[National Physical Laboratory (United Kingdom)|National Physical Laboratory (NPL)]]. He presented a paper on 19 February 1946, which was the first detailed design of a [[stored-program computer]].<ref>{{Harvnb|Copeland|2006|p=108}}</ref> [[John von Neumann|Von Neumann]]'s incomplete ''[[First Draft of a Report on the EDVAC]]'' had predated Turing's paper, but it was much less detailed and, according to [[John R. Womersley]], Superintendent of the NPL Mathematics Division, it "contains a number of ideas which are Dr. Turing's own".<ref>{{cite news | last = Randell | first = Brian | author-link = Brian Randell | title = A History of Computing in the Twentieth Century: Colossus | year = 1980 | url = http://www.cs.ncl.ac.uk/research/pubs/books/papers/133.pdf | access-date = 27 January 2012 | archive-url = https://web.archive.org/web/20120127144927/http://www.cs.ncl.ac.uk/research/pubs/books/papers/133.pdf | archive-date = 27 January 2012 | url-status = live }} citing {{Cite journal | last = Womersley | first = J.R. | author-link = John R. Womersley | title = 'ACE' Machine Project | journal=Executive Committee, National Physical Laboratory, Teddington, Middlesex | date = 13 February 1946 }}</ref>

Although ACE was a feasible design, the effect of the [[Official Secrets Act 1939|Official Secrets Act]] surrounding the wartime work at Bletchley Park made it impossible for Turing to explain the basis of his analysis of how a computer installation involving human operators would work.<ref>{{cite book |title=Alan Turing: The Enigma |publisher=Princeton University Press |author-link=Andrew Hodges |last=Hodges |first=Andrew |page=[https://books.google.com/books?id=4muYDwAAQBAJ&q=%22Twenty%20years%20ahead%20of%20his%20time%22 416] |year=2014 |isbn=978-0-691-16472-4}}</ref> This led to delays in starting the project and he became disillusioned. In late 1947 he returned to Cambridge for a sabbatical year during which he produced a seminal work on ''Intelligent Machinery'' that was not published in his lifetime.<ref>See {{harvnb|Copeland|2004b|pp=410–432}}</ref> While he was at Cambridge, the [[Pilot ACE]] was being built in his absence. It executed its first program on 10 May 1950, and a number of later computers around the world owe much to it, including the [[English Electric DEUCE]] and the American [[Bendix G-15]]. The full version of Turing's ACE was not built until after his death.<ref>{{cite web|url=http://www.npl.co.uk/about/history/notable-individuals/turing/|title=Turing at NPL|access-date=3 July 2015|archive-url=https://web.archive.org/web/20150705082340/http://www.npl.co.uk/about/history/notable-individuals/turing/|archive-date=5 July 2015|url-status=live}}</ref>

According to the memoirs of the German computer pioneer [[Heinz Billing]] from the [[Max Planck Institute for Physics]], published by Genscher, Düsseldorf, there was a meeting between Turing and [[Konrad Zuse]].<ref>{{cite web|url=http://www.mathcomp.leeds.ac.uk/turing2012/Images/Turing_Zuse.pdf|title=Did Alan Turing interrogate Konrad Zuse in Göttingen in 1947?|author=Bruderer, Herbert|access-date=7 February 2013|archive-url=https://web.archive.org/web/20130521211106/http://www.mathcomp.leeds.ac.uk/turing2012/Images/Turing_Zuse.pdf|archive-date=21 May 2013|url-status=live}}</ref> It took place in [[Göttingen]] in 1947. The interrogation had the form of a colloquium. Participants were Womersley, Turing, Porter from England and a few German researchers like Zuse, Walther, and Billing (for more details see Herbert Bruderer, ''Konrad Zuse und die Schweiz'').

[[File:Alan Turing Blue Plaque, University of Manchester.jpg|thumb|right|A [[blue plaque]] commmemorating Alan Turing's work at the [[University of Manchester]] where he was a [[Reader (academic rank)|Reader]] from 1948 to 1954]]

In 1948, Turing was appointed [[Reader (academic rank)|reader]] in the [[School of Mathematics, University of Manchester|Mathematics Department]] at the [[University of Manchester]]. He lived at "Copper Folly", 43 Adlington Road, in [[Wilmslow]].<ref>{{Cite web|url=https://www.manchestereveningnews.co.uk/news/greater-manchester-news/alan-turing-enigma-machine-home-20918089|title=Alan Turing's home could be yours - for £1.1m|first=Charlotte|last=Dobson|date=28 June 2021|website=Manchester Evening News}}</ref> A year later, he became deputy director of the Computing Machine Laboratory, where he worked on software for one of the earliest [[Von Neumann architecture|stored-program]] computers—the [[Manchester Mark 1]]. Turing wrote the first version of the Programmer's Manual for this machine, and was recruited by Ferranti as a consultant in the development of their commercialised machine, the Ferranti Mark 1. He continued to be paid consultancy fees by Ferranti until his death.<ref>{{Cite book|url=https://www.manturing.net/|title=Alan Turing's Manchester|last=Swinton|first=Jonathan|publisher=Infang Publishing|year=2019|isbn=978-0-9931789-2-4|location=Manchester|access-date=18 March 2019|archive-url=https://web.archive.org/web/20190217172318/https://www.manturing.net/|archive-date=17 February 2019|url-status=live}}</ref> During this time, he continued to do more abstract work in mathematics,<ref name="doi10.1093/qjmam/1.1.287">{{Cite journal|last1 = Turing |first1 = A.M.|doi = 10.1093/qjmam/1.1.287 |title = Rounding-Off Errors in Matrix Processes |journal = The Quarterly Journal of Mechanics and Applied Mathematics |volume = 1| pages = 287–308 |year = 1948| issue=1 |hdl = 10338.dmlcz/103139|doi-access = free }}</ref> and in "[[Computing Machinery and Intelligence]]",<ref name=mind>{{cite q|Q772056}}</ref> Turing addressed the problem of [[artificial intelligence]], and proposed an experiment that became known as the [[Turing test]], an attempt to define a standard for a machine to be called "intelligent". The idea was that a computer could be said to "think" if a human interrogator could not tell it apart, through conversation, from a human being.<ref>{{Cite book |author-link=Stevan Harnad |last=Harnad |first=Stevan |year=2008 |chapter-url=http://eprints.soton.ac.uk/262954/ |chapter=The Annotation Game: On Turing (1950) on Computing, Machinery and Intelligence |archive-url=https://web.archive.org/web/20171018070225/https://eprints.soton.ac.uk/262954/ |archive-date=18 October 2017 |editor1-last=Epstein |editor1-first=Robert |editor2-last=Peters |editor2-first=Grace |title=Parsing the Turing Test: Philosophical and Methodological Issues in the Quest for the Thinking Computer |publisher=Springer|isbn=9781402067082 }}</ref> In the paper, Turing suggested that rather than building a program to simulate the adult mind, it would be better to produce a simpler one to simulate a child's mind and then to subject it to a course of education. A [[Turing test#Reverse Turing test and CAPTCHA|reversed]] form of the Turing test is widely used on the Internet; the [[CAPTCHA]] test is intended to determine whether the user is a human or a computer.

In 1948, Turing, working with his former undergraduate colleague, [[D.G. Champernowne]], began writing a [[chess]] program for a computer that did not yet exist. By 1950, the program was completed and dubbed the [[Turochamp]].<ref>{{cite magazine|last=Clark|first=Liat|title=Turing's achievements: codebreaking, AI and the birth of computer science|url=https://www.wired.co.uk/news/archive/2012-06/18/turing-contributions?page=all|magazine=Wired|access-date=11 November 2013|archive-url=https://web.archive.org/web/20131102122933/http://www.wired.co.uk/news/archive/2012-06/18/turing-contributions?page=all|archive-date=2 November 2013|url-status=live}}</ref> In 1952, he tried to implement it on a [[Ferranti Mark 1]], but lacking enough power, the computer was unable to execute the program. Instead, Turing "ran" the program by flipping through the pages of the algorithm and carrying out its instructions on a chessboard, taking about half an hour per move. The game was recorded.<ref>{{Cite web |url=http://www.chessgames.com/perl/chessgame?gid=1356927 |title=Alan Turing vs Alick Glennie (1952) "Turing Test" |archive-url=https://web.archive.org/web/20060219033248/http://www.chessgames.com/perl/chessgame?gid=1356927 |archive-date=19 February 2006 |website=Chessgames.com}}</ref> According to [[Garry Kasparov]], Turing's program "played a recognizable game of chess".<ref>{{Cite news |last=Kasparov |first=Garry |title=Smart machines will free us all |newspaper=The Wall Street Journal |date=15–16 April 2017 |page=c3}}</ref> The program lost to Turing's colleague [[Alick Glennie]], although it is said that it won a game against Champernowne's wife, Isabel.<ref>{{mactutor|id=Champernowne|title=David Gawen Champernowne}}</ref>

His Turing test was a significant, characteristically provocative, and lasting contribution to the debate regarding artificial intelligence, which continues after more than half a century.<ref>{{Cite journal | last1 = Pinar Saygin | first1 = A. | last2 = Cicekli | first2 = I. | last3 = Akman | first3 = V. | journal = Minds and Machines | volume = 10 | issue = 4 | pages = 463–518 | year = 2000 |title=Turing Test: 50 Years Later| doi = 10.1023/A:1011288000451 | hdl = 11693/24987 | s2cid = 990084 | hdl-access = free }}</ref>

===Pattern formation and mathematical biology===
When Turing was 39 years old in 1951, he turned to [[Mathematical and theoretical biology|mathematical biology]], finally publishing his masterpiece "[[The Chemical Basis of Morphogenesis]]" in January 1952. He was interested in [[morphogenesis]], the development of patterns and shapes in biological organisms. He suggested that a system of chemicals reacting with each other and diffusing across space, termed a [[reaction–diffusion system]], could account for "the main phenomena of morphogenesis".<ref name=chemical>{{cite Q|Q769913 }}</ref> He used systems of [[partial differential equations]] to model catalytic chemical reactions. For example, if a catalyst A is required for a certain chemical reaction to take place, and if the reaction produced more of the catalyst A, then we say that the reaction is [[autocatalytic]], and there is positive feedback that can be modelled by nonlinear differential equations. Turing discovered that patterns could be created if the chemical reaction not only produced catalyst A, but also produced an inhibitor B that slowed down the production of A. If A and B then diffused through the container at different rates, then you could have some regions where A dominated and some where B did. To calculate the extent of this, Turing would have needed a powerful computer, but these were not so freely available in 1951, so he had to use linear approximations to solve the equations by hand. These calculations gave the right qualitative results, and produced, for example, a uniform mixture that oddly enough had regularly spaced fixed red spots. The Russian biochemist [[Boris Pavlovich Belousov|Boris Belousov]] had performed experiments with similar results, but could not get his papers published because of the contemporary prejudice that any such thing violated the [[second law of thermodynamics]]. Belousov was not aware of Turing's paper in the ''[[Philosophical Transactions of the Royal Society]]''.<ref>{{Cite book |first=John |last=Gribbin |title=Deep Simplicity |page=126 |publisher=Random House |year=2004}}</ref>

Although published before the structure and role of [[DNA]] was understood, Turing's work on morphogenesis remains relevant today and is considered a seminal piece of work in mathematical biology.<ref>{{cite web|url=http://www.swintons.net/deodands/archives/000087.html |title=Turing's Last, Lost work |access-date=28 November 2011 |url-status=dead |archive-url=https://web.archive.org/web/20030823032620/http://www.swintons.net/deodands/archives/000087.html |archive-date=23 August 2003 }}</ref> One of the early applications of Turing's paper was the work by James Murray explaining spots and stripes on the fur of cats, large and small.<ref>{{cite journal | last=Murray | first=James D. | title=How the Leopard Gets Its Spots | journal=Scientific American  | volume=258 | issue=3 | date=March 1988 | jstor=24989019 | pages=80–87 | doi=10.1038/scientificamerican0388-80 | bibcode=1988SciAm.258c..80M }}</ref><ref>{{Cite book |first=James D. |last=Murray |title=Mathematical Biology I |year=2007 |chapter=Chapter 6 |publisher=Springer Verlag}}</ref><ref>{{Cite book |first=John |last=Gribbin |title=Deep Simplicity |page=134 |publisher=Random House |year=2004}}</ref> Further research in the area suggests that Turing's work can partially explain the growth of "feathers, hair follicles, the branching pattern of lungs, and even the left-right asymmetry that puts the heart on the left side of the chest".<ref>{{cite journal|doi=10.1126/science.338.6113.1406|pmid=23239707|title=Turing Pattern Fingered for Digit Formation|journal=Science|volume=338|issue=6113|pages=1406|year=2012|last1=Vogel|first1=G.|bibcode=2012Sci...338.1406V}}</ref> In 2012, Sheth, et al. found that in mice, removal of [[Hox genes]] causes an increase in the number of digits without an increase in the overall size of the limb, suggesting that Hox genes control digit formation by tuning the wavelength of a Turing-type mechanism.<ref>{{Cite journal |last1 = Sheth |first1 = R. |last2 = Marcon |first2 = L. |last3 = Bastida |first3 = M.F. |last4 = Junco |first4 = M. |last5 = Quintana |first5 = L. |last6 = Dahn |first6 = R. |last7 = Kmita |first7 = M. |last8 = Sharpe |first8 = J. |last9 = Ros |first9 = M.A. |doi = 10.1126/science.1226804 |title = Hox Genes Regulate Digit Patterning by Controlling the Wavelength of a Turing-Type Mechanism |journal = Science |volume = 338 |issue = 6113 |pages = 1476–1480 |year = 2012 |pmid = 23239739 |pmc = 4486416 |bibcode = 2012Sci...338.1476S }}</ref> Later papers were not available until ''Collected Works of A.&nbsp;M.&nbsp;Turing'' was published in 1992.<ref>{{cite web|title=The Alan Turing Bibliography|url=http://www.turing.org.uk/sources/biblio3.html|page=morphogenesis|publisher=turing.org.uk|access-date=27 July 2015|author=Andrew Hodges|archive-url=https://web.archive.org/web/20150905180420/http://www.turing.org.uk/sources/biblio3.html|archive-date=5 September 2015|url-status=live}}</ref>

A study conducted in 2023 confirmed Turing's mathematical model hypothesis. Presented by the [[American Physical Society]], the experiment involved growing [[chia seed]]s in even layers within trays, later adjusting the available moisture. Researchers experimentally tweaked the factors which appear in the Turing equations, and, as a result, patterns resembling those seen in natural environments emerged. This is believed to be the first time that experiments with living vegetation have verified Turing's mathematical insight.<ref>{{cite news|url=https://www.sciencenews.org/article/seeds-alan-turing-patterns-nature-math|author=James R. Riordon|date=26 March 2023|title=Chia seedlings verify Alan Turing's ideas about patterns in nature|work=Science News|access-date=26 August 2024|archive-date=2 July 2024|archive-url=https://web.archive.org/web/20240702160511/https://www.sciencenews.org/article/seeds-alan-turing-patterns-nature-math|url-status=live}}</ref><ref>{{cite news|url=https://meetings.aps.org/Meeting/MAR23/Session/F46.3|author=Brendan D'Aquino|date=7 March 2023|title=Abstract: F46.00003 : Studying Turing patterns in vegetation|work=American Physical Society|access-date=26 August 2024|archive-date=2 July 2024|archive-url=https://web.archive.org/web/20240702162242/https://meetings.aps.org/Meeting/MAR23/Session/F46.3|url-status=live}}</ref>

==Personal life==
===Treasure===
In the 1940s, Turing became worried about losing his savings in the event of a German invasion. In order to protect it, he bought two [[Silver as an investment|silver bars]] weighing {{cvt|3200|oz|kg|-1}} and worth £250 (in 2022, £8,000 adjusted for inflation, £48,000 at spot price) and buried them in a wood near Bletchley Park.<ref>{{Cite book |last=Myrberg Burström |first=Nanouschka |url=https://www.academia.edu/13683478 |title=A tale of buried treasure, some good estimations, and golden unicorns: The numismatic connections of Alan Turing |publisher=Svenska Numismatiska Föreningen |year=2015 |isbn=9789197942720 |location=Stockholm |pages=226–230 |language=en |access-date=26 August 2024 |archive-date=2 July 2024 |archive-url=https://web.archive.org/web/20240702161450/https://www.academia.edu/13683478 |url-status=live }}</ref> Upon returning to dig them up, Turing found that he was unable to break his own code describing where exactly he had hidden them. This, along with the fact that the area had been renovated, meant that he never regained the silver.<ref>{{Cite book |last=Hodges |first=Andrew |title=Alan Turing: the enigma |publisher=Princeton University Press |year=2014 |isbn=9780691164724 |location=United States of America |pages=643 |language=en}}</ref>

===Engagement===
In 1941, Turing proposed marriage to Hut 8 colleague [[Joan Clarke]], a fellow mathematician and cryptanalyst, but their engagement was short-lived. After admitting his homosexuality to his fiancée, who was reportedly "unfazed" by the revelation, Turing decided that he could not go through with the marriage.<ref>{{Harvnb|Leavitt|2007|pp=176–178}}</ref>

===Homosexuality and indecency conviction===
[[Image:Dancehouse.jpg|thumb|left|The [[Dancehouse|Dancehouse Theatre]], formerly the Regal Cinema, pictured in 2006, outside of which Turing met Arnold Murray]]
In December 1951, Turing met Arnold Murray, a 19-year-old unemployed man. Turing was walking along Manchester's [[Wilmslow Road|Oxford Road]] when he met Murray just outside the [[Dancehouse|Regal Cinema]] and invited him to lunch. The two agreed to meet again and in January 1952 began an intimate relationship.<ref>{{Cite web |title=Alan Turing |url=https://spartacus-educational.com/Alan_Turing.htm |access-date=22 July 2023 |website=Spartacus Educational |language=en |archive-date=25 November 2021 |archive-url=https://web.archive.org/web/20211125054932/https://spartacus-educational.com/Alan_Turing.htm |url-status=live }}</ref>  On 23 January, Turing's house in Wilmslow was burgled. Murray told Turing that he and the burglar were acquainted, and Turing reported the crime to the police. During the investigation, he acknowledged a sexual relationship with Murray. Homosexual acts were criminal offences in the United Kingdom at that time,<ref>{{Harvnb|Hodges|1983|p=458}}</ref> and both men were charged with "[[gross indecency]]" under [[Criminal Law Amendment Act 1885#Section 11|Section 11]] of the [[Criminal Law Amendment Act 1885]].<ref name="LeavittP268">{{Harvnb|Leavitt|2007|p=268}}</ref> Initial [[committal procedure|committal proceedings]] for the trial were held on 27 February during which Turing's solicitor "reserved his defence", i.e., did not argue or provide evidence against the allegations. The proceedings were held at the [[Sessions House, Knutsford|Sessions House]] in [[Knutsford]].<ref>{{Cite news|url=https://www.manchestereveningnews.co.uk/news/nostalgia/historic-courthouse-near-manchester-famous-26261769|title=Historic courthouse near Manchester where famous trial took place unrecognisable after stunning renovation|date=20 February 2023|newspaper=Manchester Evenings News|access-date=5 April 2023|archive-date=5 April 2023|archive-url=https://web.archive.org/web/20230405175213/https://www.manchestereveningnews.co.uk/news/nostalgia/historic-courthouse-near-manchester-famous-26261769|url-status=live}}</ref>

Turing was later convinced by the advice of his brother and his own solicitor, and he entered a plea of guilty.<ref>{{cite book |title=Alan Turing: The Enigma |publisher=Princeton University Press |author-link=Andrew Hodges |last=Hodges |first=Andrew |page=[https://archive.org/details/alanturingenigma0000hodg/page/463 463] |year=2012 |isbn=978-0-691-15564-7 |url=https://archive.org/details/alanturingenigma0000hodg|url-access=registration }}</ref> The case, ''[[Elizabeth II|Regina]] v. Turing and Murray,'' was brought to trial on 31 March 1952.<ref>{{cite book |title=Alan Turing: The Enigma |publisher=Princeton University Press |author-link=Andrew Hodges |last=Hodges |first=Andrew |page=[https://archive.org/details/alanturingenigma0000hodg/page/471 471] |year=2012 |isbn=978-0-691-15564-7 |url=https://archive.org/details/alanturingenigma0000hodg|url-access=registration }}</ref> Turing was convicted and given a choice between imprisonment and probation. His probation would be conditional on his agreement to undergo [[hormone|hormonal]] physical changes designed to reduce [[libido]], known as "[[chemical castration]]".<ref name=":2">{{Cite journal |last=Peralta |first=René |date=23 June 2022 |title=Alan Turing's Everlasting Contributions to Computing, AI and Cryptography |url=https://www.nist.gov/blogs/taking-measure/alan-turings-everlasting-contributions-computing-ai-and-cryptography |journal=NIST |language=en |access-date=26 August 2024 |archive-date=23 August 2024 |archive-url=https://web.archive.org/web/20240823194432/https://www.nist.gov/blogs/taking-measure/alan-turings-everlasting-contributions-computing-ai-and-cryptography |url-status=live }}</ref> He accepted the option of injections of what was then called stilboestrol (now known as [[diethylstilbestrol]] or DES), a synthetic [[oestrogen]]; this feminization of his body was continued for the course of one year. The treatment rendered Turing [[impotence|impotent]] and caused [[gynaecomastia|breast tissue to form]].<ref>{{cite book | title=Alan Turing: The Enigma The Centenary Edition | publisher=Princeton University | author= Hodges, Andrew | year=2012}}</ref> In a letter, Turing wrote that "no doubt I shall emerge from it all a different man, but quite who I've not found out".<ref>{{cite web |title=Letters of Note: Yours in distress, Alan |last=Turing |first=Alan |year=1952 |url=http://www.lettersofnote.com/2012/06/yours-in-distress-alan.html |archive-date=20 January 2013 |archive-url=https://web.archive.org/web/20130120024901/http://www.lettersofnote.com/2012/06/yours-in-distress-alan.html |url-status=dead |access-date=16 December 2012 }}</ref><ref>{{cite book |title=Alan Turing: The Enigma |publisher=Princeton University Press |author-link=Andrew Hodges |last=Hodges |first=Andrew |page=xxviii |year= 2012 |isbn=978-0-691-15564-7 |url=https://archive.org/details/alanturingenigma0000hodg|url-access=registration }}</ref> Murray was given a conditional discharge.<ref>{{Harvnb|Hodges|1983|p=473}}</ref>

Turing's conviction led to the removal of his security clearance and barred him from continuing with his cryptographic consultancy for [[GCHQ]], the British [[signals intelligence]] agency that had evolved from GC&CS in 1946, though he kept his academic post. His trial took place only months after the defection to the Soviet Union of [[Guy Burgess]] and [[Donald Maclean (spy)|Donald Maclean]], in summer 1951, after which the Foreign Office started to consider anyone known to be homosexual as a potential security risk.<ref>{{cite web|url=https://theconversation.com/revealed-the-panic-that-followed-the-defection-of-the-cambridge-spies-49623|title=The Panic that followed the defection of the Cambridge spies|website=The Conversation|date=23 October 2015|access-date=12 August 2023|archive-date=13 August 2023|archive-url=https://web.archive.org/web/20230813085159/https://theconversation.com/revealed-the-panic-that-followed-the-defection-of-the-cambridge-spies-49623|url-status=live}}</ref>

Turing was denied entry into the United States after his conviction in 1952, but was free to visit other European countries.<ref>{{Harvnb|Copeland|2006|p=143}}</ref> In the summer of 1952 he visited Norway which was more tolerant of homosexuals. Among the various men he met there was one named Kjell Carlson. Kjell intended to visit Turing in the UK but the authorities intercepted Kjell's postcard detailing his travel arrangements and were able to intercept and deport him before the two could meet.<ref name="olinick13">{{Cite book |last=Olinick |first=Michael |year=2021 |title=Simply Turing |location=United States |publisher=Simply Charly |chapter=Chapter 13}}</ref> It was also during this time that Turing started consulting a psychiatrist, Dr Franz Greenbaum, with whom he got on well and who subsequently became a family friend.<ref name=olinick13/><ref name=dowd/>

==Death==
[[File:Turing_Plaque.jpg|thumb|right|A [[blue plaque]] on the house at 43 Adlington Road, [[Wilmslow]], where Turing lived and died<ref name=copperfolly/>]]
On 8 June 1954, at his house at 43 Adlington Road, [[Wilmslow]], Turing's housekeeper found him dead.<ref name=copperfolly>{{cite web|archive-url=https://web.archive.org/web/20210703105309/https://assets.savills.com/properties/GBWSRSWIS210139/WIS210139_WIS21003746.PDF|archive-date=3 July 2021|url=https://assets.savills.com/properties/GBWSRSWIS210139/WIS210139_WIS21003746.PDF|website=savills.com|author=Anon|year=2021|title=Turing's House: Copper Folly, 43 Adlington Road, Wilmslow, Cheshire, SK9 2BJ}}</ref> A post mortem was held that evening, which determined that he had died the previous day at age 41 with [[cyanide poisoning]] cited as the cause of death.<ref>{{cite web|url=https://turingarchive.kings.cam.ac.uk/material-given-kings-college-cambridge-1960-amtk/amt-k-6|title=Post Mortem Examination|website=Turing Digital Archive|access-date=26 August 2024|archive-date=15 July 2024|archive-url=https://web.archive.org/web/20240715235055/https://turingarchive.kings.cam.ac.uk/material-given-kings-college-cambridge-1960-amtk/amt-k-6|url-status=live}}</ref><ref>{{Cite encyclopedia |url=https://www.britannica.com/biography/Alan-Turing#toc330986 |title=Alan Turing. Biography, Facts, & Education |encyclopedia=Encyclopædia Britannica |access-date=11 October 2017 |archive-url=https://web.archive.org/web/20171011184445/https://www.britannica.com/biography/Alan-Turing#toc330986 |archive-date=11 October 2017 |url-status=live }}</ref> When his body was discovered, an apple lay half-eaten beside his bed, and although the apple was not tested for cyanide,<ref>{{Harvnb|Hodges|1983|p=488}}</ref> it was speculated that this was the means by which Turing had consumed a fatal dose.

Turing's brother, John, identified the body the following day and took the advice given by Dr. Greenbaum to accept the verdict of the [[Inquests in England and Wales|inquest]], as there was little prospect of establishing that the death was accidental.<ref name="reflections">{{cite book|title=Reflections of Alan Turing|last=Turing|first=Dermot|publisher=The History Press |year=2021 |isbn=9781803990125}}</ref> The inquest was held the following day, which determined the cause of death to be suicide.<ref name=":2" /> Turing's remains were cremated at [[Woking Crematorium]] just two days later on 12 June 1954, with just his mother, brother, and Lyn Newman attending,<ref>{{cite book|title=Alan Turing: Guildford's best kept secret|last=Backhouse|first=Paul|publisher=Guildford Town Guides |year=2016}}</ref><ref>{{Harvnb|Hodges|1983|p=529}}</ref> and his ashes were scattered in the gardens of the crematorium, just as his father's had been.<ref name="hodges2012">{{cite book |url=https://books.google.com/books?id=EpAl0piM38cC |title=Alan Turing: The Enigma |last=Hodges |first=Andrew |date=2012 |publisher=Random House |isbn=978-1-4481-3781-7 |access-date=16 January 2019 |archive-url=https://web.archive.org/web/20190117070027/https://books.google.co.uk/books?id=EpAl0piM38cC |archive-date=17 January 2019 |url-status=live }}</ref> Turing's mother was on holiday in Italy at the time of his death and returned home after the inquest. She never accepted the verdict of suicide.<ref name=reflections/>

Philosopher [[Jack Copeland]] has questioned various aspects of the coroner's historical verdict. He suggested an alternative explanation for the cause of Turing's death: the accidental inhalation of cyanide fumes from an apparatus used to [[electroplating|electroplate]] gold onto spoons. The [[potassium cyanide]] was used to [[Gold#Chemistry|dissolve the gold]]. Turing had such an apparatus set up in his tiny spare room. Copeland noted that the autopsy findings were more consistent with inhalation than with ingestion of the poison. Turing also habitually ate an apple before going to bed, and it was not unusual for the apple to be discarded half-eaten.<ref name = "Copeland">{{cite news | first = Roland | last = Pease | title = Alan Turing: Inquest's suicide verdict 'not supportable' | url = https://www.bbc.co.uk/news/science-environment-18561092 | work = [[BBC News]] | date = 23 June 2012 | access-date = 23 June 2012 | quote = We have&nbsp;... been recreating the narrative of Turing's life, and we have recreated him as an unhappy young man who committed suicide. But the evidence is not there. | archive-url = https://web.archive.org/web/20120623101625/http://www.bbc.co.uk/news/science-environment-18561092 | archive-date = 23 June 2012 | url-status = live }}</ref> Furthermore, Turing had reportedly borne his legal setbacks and hormone treatment (which had been discontinued a year previously) "with good humour" and had shown no sign of despondency before his death. He even set down a list of tasks that he intended to complete upon returning to his office after the holiday weekend.<ref name = "Copeland"/> Turing's mother believed that the ingestion was accidental, resulting from her son's careless storage of laboratory chemicals.<ref>{{cite web |url=https://www.christies.com/lotfinder/lot_details.aspx?intObjectID=5685694 |title=TURING, Ethel Sara (1881–1976, mother of Alan Turing). Series of 11 autograph letters to Robin Gandy, Guilford, 28 July 1954 – 11 June 1971 (most before 1959), altogether 29 pages, 8vo (2 letters dated 17 May and 26 May 1955 incomplete, lacking continuation leaves, occasional light soiling) |website=christies.com |access-date=6 February 2019 |archive-url=https://web.archive.org/web/20190207015923/https://www.christies.com/lotfinder/lot_details.aspx?intObjectID=5685694 |archive-date=7 February 2019 |url-status=live }}</ref> Turing biographer [[Andrew Hodges]] theorised that Turing deliberately made his death look accidental in order to shield his mother from the knowledge that he had killed himself.<ref>{{Harvnb|Hodges|1983|pp=488, 489}}</ref>

Doubts on the suicide thesis have been also cast by [[John W. Dawson Jr.]] who, in his review of Hodges' book, recalls "Turing's vulnerable position in the Cold War political climate" and points out that "Turing was found dead by a maid, who discovered him 'lying neatly in his bed'—hardly what one would expect of "a man fighting for life against the suffocation induced by cyanide poisoning." Turing had given no hint of suicidal inclinations to his friends and had made no effort to put his affairs in order.<ref>{{cite journal |last= Dawson Jr. |first=John W. |author-link=John W. Dawson Jr. |title="Review of Andrew Hodges. Alan Turing: the enigma" |journal=[[Journal of Symbolic Logic]] |volume=50 |issue=4 |date=December 1985 |pages=1065–1067 |doi=10.2307/2273992 |jstor=2273992 |url=https://doi.org/10.2307/2273992}}</ref>

Hodges and a later biographer, [[David Leavitt]], have both speculated that Turing was re-enacting a scene from the [[Walt Disney]] film ''[[Snow White and the Seven Dwarfs (1937 film)|Snow White and the Seven Dwarfs]]'' (1937), his favourite fairy tale. Both men noted that (in Leavitt's words) he took "an especially keen pleasure in the scene where the Wicked Queen immerses her apple in the poisonous brew".<ref>{{Harvnb|Leavitt|2007|p=140}} and {{Harvnb|Hodges|1983|pp=149, 489}}</ref>
[[File:Alan Turing OBE.jpg|thumb|Turing's OBE currently held in [[Sherborne School]] archives]]

It has also been suggested that Turing's belief in [[fortune-telling]] may have caused his depressed mood.<ref name="hodges2012" /> As a youth, Turing had been told by a fortune-teller that he would be a genius. In mid-May 1954, shortly before his death, Turing again decided to consult a fortune-teller during a day-trip to [[Lytham St Annes|St Annes-on-Sea]] with the Greenbaum family.<ref name="hodges2012"/> According to the Greenbaums' daughter, Barbara:<ref name="dowd">{{cite web |url=https://www.bbc.co.uk/news/magazine-27701207 |title=What was Alan Turing really like? |author=Vincent Dowd |publisher=BBC |date=6 June 2014 |access-date=16 January 2019 |archive-url=https://web.archive.org/web/20190117020715/https://www.bbc.co.uk/news/magazine-27701207 |archive-date=17 January 2019 |url-status=live }}</ref>

{{blockquote|But it was a lovely sunny day and Alan was in a cheerful mood and off we went&nbsp;... Then he thought it would be a good idea to go to the [[Blackpool Pleasure Beach|Pleasure Beach at Blackpool]]. We found a fortune-teller's tent and Alan said he'd like to go in[,] so we waited around for him to come back&nbsp;... And this sunny, cheerful visage had shrunk into a pale, shaking, horror-stricken face. Something had happened. We don't know what the fortune-teller said but he obviously was deeply unhappy. I think that was probably the last time we saw him before we heard of his suicide.}}

==Government apology and pardon==
{{main|Alan Turing law}}

In August 2009, British programmer [[John Graham-Cumming]] started a petition urging the British government to apologise for Turing's prosecution as a homosexual.<ref>{{Cite news |title=Thousands call for Turing apology |url=http://news.bbc.co.uk/2/hi/technology/8226509.stm |work=BBC News |date=31 August 2009 |access-date=31 August 2009 |archive-url=https://web.archive.org/web/20090831100747/http://news.bbc.co.uk/2/hi/technology/8226509.stm |archive-date=31 August 2009 |url-status=live }}</ref><ref>{{Cite book|title=Petition seeks apology for Enigma code-breaker Turing |url=http://www.cnn.com/2009/WORLD/europe/09/01/alan.turing.petition/index.html |publisher=CNN |date=1 September 2009 |access-date=1 September 2009 |archive-url=https://web.archive.org/web/20091005081407/http://www.cnn.com/2009/WORLD/europe/09/01/alan.turing.petition/index.html |archive-date=5 October 2009 |url-status=live }}</ref> The petition received more than 30,000 signatures.<ref name="PMapology"/><ref>The petition was only open to UK citizens.</ref> The prime minister, [[Gordon Brown]], acknowledged the petition, releasing a statement on 10 September 2009 apologising and describing the treatment of Turing as "appalling":<ref name="PMapology">{{cite news | title = PM's apology to codebreaker Alan Turing: we were inhumane | url = https://www.theguardian.com/world/2009/sep/11/pm-apology-to-alan-turing | work = The Guardian | location = UK | date = 11 September 2009 | first = Caroline | last = Davies | access-date = 10 December 2016 | archive-url = https://web.archive.org/web/20170204085908/https://www.theguardian.com/world/2009/sep/11/pm-apology-to-alan-turing | archive-date = 4 February 2017 | url-status = live }}</ref><ref name="PM-apology">{{cite news | url = http://news.bbc.co.uk/2/hi/technology/8249792.stm | title = PM apology after Turing petition | date = 11 September 2009 | work = BBC News | access-date = 11 September 2009 | archive-url = https://web.archive.org/web/20120531004935/http://news.bbc.co.uk/2/hi/technology/8249792.stm | archive-date = 31 May 2012 | url-status = live }}</ref>

{{blockquote|Thousands of people have come together to demand justice for Alan Turing and recognition of the appalling way he was treated. While Turing was dealt with under the law of the time and we can't put the clock back, his treatment was of course utterly unfair and I am pleased to have the chance to say how deeply sorry I and we all are for what happened to him&nbsp;... So on behalf of the British government, and all those who live freely thanks to Alan's work I am very proud to say: we're sorry, you deserved so much better.<ref name="PMapology"/><ref>{{Cite web |url=http://www.cs.auckland.ac.nz/~ian/TuringApology.html |title=Full text of the Prime Minister's apology |archive-url=https://web.archive.org/web/20121109124247/http://www.cs.auckland.ac.nz/~ian/TuringApology.html |archive-date=9 November 2012 }}</ref>}}

In December 2011, William Jones and his member of Parliament, [[John Leech (politician)|John Leech]], created an [[e-petition]]<ref name="PardonPetition">{{cite web | title = Grant a pardon to Alan Turing | url = https://submissions.epetitions.direct.gov.uk/petitions/23526 | date = 6 December 2011 | url-status=dead | archive-url = https://web.archive.org/web/20120110183548/http://submissions.epetitions.direct.gov.uk/petitions/23526 | archive-date = 10 January 2012 | df = dmy-all }}</ref> requesting that the British government [[pardon]] Turing for his conviction of "gross indecency":<ref name="BBBCPardon">{{cite news | title = Petition to pardon computer pioneer Alan Turing started | url = https://www.bbc.co.uk/news/uk-england-manchester-16061279 | date = 6 December 2011 | work = BBC News | access-date = 21 June 2018 | archive-url = https://web.archive.org/web/20180619135127/https://www.bbc.co.uk/news/uk-england-manchester-16061279 | archive-date = 19 June 2018 | url-status = live }}</ref>

{{blockquote|We ask the HM Government to grant a pardon to Alan Turing for the conviction of "gross indecency". In 1952, he was convicted of "gross indecency" with another man and was forced to undergo so-called "organo-therapy"—chemical castration. Two years later, he killed himself with cyanide, aged just 41. Alan Turing was driven to a terrible despair and early death by the nation he'd done so much to save. This remains a shame on the British government and British history. A pardon can go some way to healing this damage. It may act as an apology to many of the other gay men, not as well-known as Alan Turing, who were subjected to these laws.<ref name="PardonPetition" />}}

The petition gathered over 37,000 signatures,<ref name=PardonPetition /><ref name=turingindependent24dec2013>{{cite news |url=https://www.independent.co.uk/news/uk/home-news/alan-turing-gets-his-royal-pardon-for-gross-indecency--61-years-after-he-poisoned-himself-9023116.html |title=Alan Turing gets his royal pardon for 'gross indecency'&nbsp;– 61 years after he poisoned himself |work=The Independent |date=23 December 2013 |author=Wright, Oliver |location=London |access-date=21 August 2017 |archive-url=https://web.archive.org/web/20131224035745/http://www.independent.co.uk/news/uk/home-news/alan-turing-gets-his-royal-pardon-for-gross-indecency--61-years-after-he-poisoned-himself-9023116.html |archive-date=24 December 2013 |url-status=live }}</ref> and was submitted to Parliament by the Manchester MP John Leech but the request was discouraged by Justice Minister [[Tom McNally, Baron McNally#Political career|Lord McNally]], who said:<ref name="PardonPetitionDiscouraged">{{cite web |title=Government rejects a pardon for computer genius Alan Turing |url=https://www.theguardian.com/uk/the-northerner/2012/feb/07/alan-turing-pardon-lord-mcnally-lord-sharkey-computers |date=7 February 2012 |last=Wainwright |first=Martin |work=The Guardian |access-date=10 December 2016 |archive-url=https://web.archive.org/web/20170204091026/https://www.theguardian.com/uk/the-northerner/2012/feb/07/alan-turing-pardon-lord-mcnally-lord-sharkey-computers |archive-date=4 February 2017 |url-status=live }}</ref>

{{blockquote|A posthumous pardon was not considered appropriate as Alan Turing was properly convicted of what at the time was a criminal offence. He would have known that his offence was against the law and that he would be prosecuted. It is tragic that Alan Turing was convicted of an offence that now seems both cruel and absurd—particularly poignant given his outstanding contribution to the war effort. However, the law at the time required a prosecution and, as such, long-standing policy has been to accept that such convictions took place and, rather than trying to alter the historical context and to put right what cannot be put right, ensure instead that we never again return to those times.<ref>{{cite web |url=https://publications.parliament.uk/pa/ld201212/ldhansrd/text/120202w0001.htm |title=hansard |publisher=Parliament of the United Kingdom |date=2 February 2012 |access-date=29 August 2017 |archive-url=https://web.archive.org/web/20170706132556/https://www.publications.parliament.uk/pa/ld201212/ldhansrd/text/120202w0001.htm |archive-date=6 July 2017 |url-status=live }}</ref>}}

John Leech, the MP for [[Manchester Withington (UK Parliament constituency)|Manchester Withington]] (2005–15), submitted several bills to Parliament<ref>{{cite web|url=http://www.politics.co.uk/news/2013/12/24/better-late-than-never-alan-turing-is-finally-pardoned|title=Better late than never, Alan Turing is finally pardoned|first=Alex|last=Stevenson|date=24 December 2013|publisher=politics.co.uk|access-date=25 September 2016|archive-url=https://web.archive.org/web/20160816015157/http://www.politics.co.uk/news/2013/12/24/better-late-than-never-alan-turing-is-finally-pardoned|archive-date=16 August 2016|url-status=live}}</ref> and led a high-profile campaign to secure the pardon. Leech made the case in the House of Commons that Turing's contribution to the war made him a national hero and that it was "ultimately just embarrassing" that the conviction still stood.<ref name="Fitzgerald">{{cite web|url=http://www.manchestereveningnews.co.uk/news/greater-manchester-news/alan-turings-court-convictions-go-11931942|title=Alan Turing's court convictions go on display for the first time|first=Todd|last=Fitzgerald|date=24 September 2016|publisher=manchestereveningnews.co.uk|access-date=25 September 2016|archive-url=https://web.archive.org/web/20160925151625/http://www.manchestereveningnews.co.uk/news/greater-manchester-news/alan-turings-court-convictions-go-11931942|archive-date=25 September 2016|url-status=live}}</ref> Leech continued to take the bill through Parliament and campaigned for several years, gaining the public support of numerous leading scientists, including [[Stephen Hawking]].<ref>{{Cite news|url=https://www.manchestereveningnews.co.uk/news/greater-manchester-news/manchester-codebreaker-alan-turing-pardoned-6442836|title=Alan Turing pardoned by The Queen for his 'unjust and discriminatory' conviction for homosexuality|last=Britton|first=Paul|work=Manchester Evening News|date=24 December 2013|access-date=24 June 2018|archive-url=https://web.archive.org/web/20180624204418/https://www.manchestereveningnews.co.uk/news/greater-manchester-news/manchester-codebreaker-alan-turing-pardoned-6442836|archive-date=24 June 2018|url-status=live}}</ref><ref>{{cite news|url=https://www.bbc.co.uk/news/uk-england-manchester-16833621|title=MP calls for pardon for computer pioneer Alan Turing|date=1 February 2012|work=BBC News|access-date=25 September 2016|archive-url=https://web.archive.org/web/20160702135251/http://www.bbc.co.uk/news/uk-england-manchester-16833621|archive-date=2 July 2016|url-status=live}}</ref> At the British premiere of a film based on Turing's life, ''[[The Imitation Game]]'', the producers thanked Leech for bringing the topic to public attention and securing Turing's pardon.<ref>{{Cite news|url=https://www.libdemvoice.org/my-proudest-day-as-a-liberal-democrat-43430.html|title=My proudest day as a Liberal Democrat|work=Liberal Democrat Voice|access-date=24 June 2018|archive-url=https://web.archive.org/web/20180624204354/https://www.libdemvoice.org/my-proudest-day-as-a-liberal-democrat-43430.html|archive-date=24 June 2018|url-status=live}}</ref> Leech is now regularly described as the "architect" of Turing's pardon and subsequently the Alan Turing Law which went on to secure pardons for 75,000 other men and women convicted of similar crimes.<ref>{{Cite web |url=https://www.manchestereveningnews.co.uk/news/greater-manchester-news/manchester-computer-pioneer-alan-turing-16585966 |title=Manchester computer pioneer Alan Turing announced as face of new £50 note |date=15 July 2019 |access-date=19 July 2019 |archive-url=https://web.archive.org/web/20190719082039/https://www.manchestereveningnews.co.uk/news/greater-manchester-news/manchester-computer-pioneer-alan-turing-16585966 |archive-date=19 July 2019 |url-status=live }}</ref><ref>{{Cite web|url=http://outnewsglobal.com/john-leech-secures-historic-deal-with-government-on-alan-turing-law/|title=John Leech secures historic deal with Government on 'Alan Turing Law'|date=20 October 2016|website=outnewsglobal.com|access-date=26 August 2024|archive-date=29 January 2022|archive-url=https://web.archive.org/web/20220129031439/http://outnewsglobal.com/john-leech-secures-historic-deal-with-government-on-alan-turing-law/|url-status=live}}</ref><ref>{{Cite news |date=15 July 2019 |editor1-last=Elliott |editor1-first=Larry |title=Alan Turing to feature on new £50 banknote |url=https://www.theguardian.com/business/2019/jul/15/alan-turing-to-feature-on-new-50-note |url-status=live |archive-url=https://web.archive.org/web/20220129025950/https://www.theguardian.com/business/2019/jul/15/alan-turing-to-feature-on-new-50-note |archive-date=29 January 2022 |access-date=26 August 2024 |newspaper=The Guardian |editor2-first=Josh |editor2-last=Halliday}}</ref>

On 26 July 2012, a bill was introduced in the [[British House of Lords|House of Lords]] to grant a statutory pardon to Turing for offences under section 11 of the Criminal Law Amendment Act 1885, of which he was convicted on 31 March 1952.<ref>{{cite web |url=http://services.parliament.uk/bills/2012-13/alanturingstatutorypardon.html |title=Bill |publisher=Parliament of the United Kingdom |date=26 July 2012 |access-date=31 October 2013 |archive-url=https://web.archive.org/web/20131102040318/http://services.parliament.uk/bills/2012-13/alanturingstatutorypardon.html |archive-date=2 November 2013 |url-status=live }}</ref> Late in the year in a letter to ''[[The Daily Telegraph]]'', the physicist Stephen Hawking and 10 other signatories including the [[Astronomer Royal]] [[Martin Rees, Baron Rees of Ludlow|Lord Rees]], [[List of presidents of the Royal Society|President of the Royal Society]] Sir [[Paul Nurse]], [[Jean Barker, Baroness Trumpington|Lady Trumpington]] (who worked for Turing during the war) and [[John Sharkey, Baron Sharkey|Lord Sharkey]] (the bill's sponsor) called on Prime Minister [[David Cameron]] to act on the pardon request.<ref>{{Cite news |last=Pearse |first=Damian |url=https://www.theguardian.com/science/2012/dec/14/alan-turing-pardon-stephen-hawking |title=Alan Turing should be pardoned, argue Stephen Hawking and top scientists |archive-url=https://web.archive.org/web/20170204090812/https://www.theguardian.com/science/2012/dec/14/alan-turing-pardon-stephen-hawking |archive-date=4 February 2017 |work=The Guardian |date=13 December 2012 |access-date=15 December 2012}}</ref> The government indicated it would support the bill,<ref name=turingguardian19july2013>{{cite news|url=https://www.theguardian.com/uk-news/2013/jul/19/enigma-codebreaker-alan-turing-posthumous-pardon|title=Enigma codebreaker Alan Turing to be given posthumous pardon|work=The Guardian|date=19 July 2013|author=Watt, Nicholas|location=London|access-date=10 December 2016|archive-url=https://web.archive.org/web/20170104124001/https://www.theguardian.com/uk-news/2013/jul/19/enigma-codebreaker-alan-turing-posthumous-pardon|archive-date=4 January 2017|url-status=live}}</ref><ref>{{cite news|url=http://www.v3.co.uk/v3-uk/news/2302744/alan-turing-pardon-moves-a-step-closer|title=Alan Turing pardon sails through House of Lords|last=Worth|first=Dan|date=30 October 2013|publisher=V3|access-date=24 December 2013|archive-url=https://web.archive.org/web/20131224114746/http://www.v3.co.uk/v3-uk/news/2302744/alan-turing-pardon-moves-a-step-closer|archive-date=24 December 2013|url-status=live}}</ref><ref>{{cite web | title =Alan Turing (Statutory Pardon) Bill | url =http://services.parliament.uk/bills/2013-14/alanturingstatutorypardon.html | access-date =20 July 2013 | archive-url =https://web.archive.org/web/20130705084023/http://services.parliament.uk/bills/2013-14/alanturingstatutorypardon.html | archive-date =5 July 2013 | url-status =live }}</ref> and it passed its third reading in the House of Lords in October.<ref name=turingpinknewsdec2013>{{cite news|url=http://www.pinknews.co.uk/2013/12/02/lib-dem-mp-john-leech-disappointed-at-delay-to-alan-turing-pardon-bill|title=Lib Dem MP John Leech disappointed at delay to Alan Turing pardon bill|newspaper=Pink News|date=2 December 2013|author=Roberts, Scott|access-date=24 December 2013|archive-url=https://web.archive.org/web/20131225050250/http://www.pinknews.co.uk/2013/12/02/lib-dem-mp-john-leech-disappointed-at-delay-to-alan-turing-pardon-bill|archive-date=25 December 2013|url-status=live}}</ref>

At the bill's second reading in the [[House of Commons of the United Kingdom|House of Commons]] on 29 November 2013, Conservative MP [[Christopher Chope]] objected to the bill, delaying its passage. The bill was due to return to the House of Commons on 28 February 2014,<ref>{{Cite news|url=https://www.pinknews.co.uk/2013/12/02/lib-dem-mp-john-leech-disappointed-at-delay-to-alan-turing-pardon-bill/|title=Lib Dem MP John Leech disappointed at delay to Alan Turing pardon bill|last=Roberts|first=Scott|date=2 December 2013|work=PinkNews|access-date=20 June 2018|archive-url=https://web.archive.org/web/20180612210914/https://www.pinknews.co.uk/2013/12/02/lib-dem-mp-john-leech-disappointed-at-delay-to-alan-turing-pardon-bill/|archive-date=12 June 2018|url-status=live}}</ref> but before the bill could be debated in the House of Commons,<ref>{{cite web | title =Alan Turing (Statutory Pardon) Bill | url =http://services.parliament.uk/bills/2013-14/alanturingstatutorypardon.html | access-date =24 December 2013 | archive-url =https://web.archive.org/web/20131102040315/http://services.parliament.uk/bills/2013-14/alanturingstatutorypardon.html | archive-date =2 November 2013 | url-status =live }}</ref> the government elected to proceed under the [[royal prerogative of mercy]]. On 24 December 2013, [[Queen Elizabeth II]] signed a [[Royal prerogative of mercy|pardon]] for Turing's conviction for "gross indecency", with immediate effect.<ref name=turingpardon24dec2013>{{cite web |url=https://www.telegraph.co.uk/history/world-war-two/10536246/Alan-Turing-granted-Royal-pardon-by-the-Queen.html |title=Alan Turing granted Royal pardon by the Queen |last=Swinford |first=Steven |date=23 December 2013 |work=The Daily Telegraph |access-date=5 April 2018 |archive-url=https://web.archive.org/web/20180502103553/https://www.telegraph.co.uk/history/world-war-two/10536246/Alan-Turing-granted-Royal-pardon-by-the-Queen.html |archive-date=2 May 2018 |url-status=dead }}</ref> Announcing the pardon, Lord Chancellor [[Chris Grayling]] said Turing deserved to be "remembered and recognised for his fantastic contribution to the war effort" and not for his later criminal conviction.<ref name=turingindependent24dec2013 /><ref name="BBC-pardon24Dec">{{cite news|title=Royal pardon for codebreaker Alan Turing|url=https://www.bbc.co.uk/news/technology-25495315|access-date=24 December 2013|work=BBC News|date=24 December 2013|archive-url=https://web.archive.org/web/20131224002121/http://www.bbc.co.uk/news/technology-25495315|archive-date=24 December 2013|url-status=live}}</ref> The Queen pronounced Turing pardoned in August 2014.<ref>{{cite web|url=http://www.advocate.com/world/2014/08/22/queens-decree-alan-turing-now-officially-pardoned|title=With Queen's Decree, Alan Turing Is Now Officially Pardoned|date=22 August 2014|publisher=Advocate.com|access-date=1 November 2014|archive-url=https://web.archive.org/web/20141101212528/http://www.advocate.com/world/2014/08/22/queens-decree-alan-turing-now-officially-pardoned|archive-date=1 November 2014|url-status=live}}</ref> It was only the fourth royal pardon granted since the conclusion of the Second World War.<ref>{{Cite magazine |title=Pardoned: Alan Turing, Computing patriarch |magazine=Time Magazine |volume=183 |number=1 |date=13 January 2014 |page=14}}</ref> Pardons are normally granted only when the person is technically innocent, and a request has been made by the family or other interested party; neither condition was met in regard to Turing's conviction.<ref name = grauniad>{{Cite news | last =Davies | first =Caroline | title = Codebreaker Turing is given posthumous royal pardon | newspaper =The Guardian | location =London | pages =1, 6 | date =24 December 2013 }}</ref>

In September 2016, the government announced its intention to expand this retroactive exoneration to other men convicted of similar historical indecency offences, in what was described as an "[[Alan Turing law]]".<ref>{{cite news|url=https://www.bbc.co.uk/news/uk-37436417|title=Government 'committed' to Alan Turing gay pardon law|date=22 September 2016|work=BBC News|access-date=22 September 2016|archive-url=https://web.archive.org/web/20160922041224/http://www.bbc.co.uk/news/uk-37436417|archive-date=22 September 2016|url-status=live}}</ref><ref>{{Cite web|url=https://www.independent.co.uk/news/uk/politics/theresa-may-committed-to-introducing-alan-turing-law-and-pardon-gay-men-convicted-of-outdated-crimes-a7320851.html|title=Theresa May committed to introducing the 'Alan Turing Law'|last=Cowburn|first=Ashley|date=21 September 2016|website=The Independent|access-date=22 September 2016|archive-url=https://web.archive.org/web/20160922133219/http://www.independent.co.uk/news/uk/politics/theresa-may-committed-to-introducing-alan-turing-law-and-pardon-gay-men-convicted-of-outdated-crimes-a7320851.html|archive-date=22 September 2016|url-status=live}}</ref> The Alan Turing law is now an informal term for the law in the United Kingdom, contained in the [[Policing and Crime Act 2017]], which serves as an [[amnesty law]] to retroactively pardon men who were cautioned or convicted under historical legislation that outlawed homosexual acts. The law applies in England and Wales.<ref>{{cite web|url=http://www.legislation.gov.uk/ukpga/2017/3/section/182/data.htm|title=Policing and Crime Act 2017|publisher=Government of the United Kingdom|access-date=6 February 2019|archive-url=https://web.archive.org/web/20190305145933/http://www.legislation.gov.uk/ukpga/2017/3/section/182/data.htm|archive-date=5 March 2019|url-status=live}}</ref>

On 19 July 2023, [[Sexual orientation and the military of the United Kingdom#Official apology to veterans|following an apology to LGBT veterans from the UK Government]], [[Secretary of State for Defence|Defence Secretary]] [[Ben Wallace (politician)|Ben Wallace]] suggested Turing should be honoured with a permanent statue on the [[Fourth plinth#Proposals for permanent statues|fourth plinth of Trafalgar Square]], describing Turing as "probably the greatest war hero, in my book, of the Second World War, [whose] achievements shortened the war, saved thousands of lives, helped defeat the Nazis. And his story is a sad story of a society and how it treated him."<ref>{{Cite web |title=Veterans Update |url=https://hansard.parliament.uk/Commons/2023-07-19/debates/56A50AFF-35D8-408F-A393-DDB38951E64F/VeteransUpdate?#contribution-43233FDB-224B-4D71-B796-BB90C501DB16 |website=Hansard – UK Parliament |access-date=24 July 2023 |archive-date=24 July 2023 |archive-url=https://web.archive.org/web/20230724123630/https://hansard.parliament.uk/Commons/2023-07-19/debates/56A50AFF-35D8-408F-A393-DDB38951E64F/VeteransUpdate#contribution-43233FDB-224B-4D71-B796-BB90C501DB16 |url-status=live }}</ref><ref>{{Cite news |title=Alan Turing statue should be put on Trafalgar Square's fourth plinth, says Ben Wallace |url=https://www.telegraph.co.uk/politics/2023/07/19/alan-turing-trafalgar-square-fourth-plinth-ben-wallace/ |website=The Telegraph |date=19 July 2023 |access-date=24 July 2023 |last1=Sheridan |first1=Danielle |archive-date=24 July 2023 |archive-url=https://web.archive.org/web/20230724123628/https://www.telegraph.co.uk/politics/2023/07/19/alan-turing-trafalgar-square-fourth-plinth-ben-wallace/ |url-status=live }}</ref><ref>{{Cite news |title=LGBTQ+ military charity backs proposal for Alan Turing statue on fourth plinth |url=https://www.theguardian.com/science/2023/jul/24/lgbtq-military-charity-backs-proposal-alan-turing-statue-fourth-plinth-trafalgar-square |website=The Guardian |date=24 July 2023 |access-date=24 July 2023 |last1=Khomami |first1=Nadia |last2=Arts |first2=Nadia Khomami }}</ref>

== See also ==
* [[Legacy of Alan Turing]]
* [[List of things named after Alan Turing]]

==References==
===Notes===
{{notelist|group=note}}

===Citations===
{{Reflist|30em}}

===Works cited===
{{Refbegin}}
* {{Cite web | last = Alexander | first = C. Hugh O'D. | title = Cryptographic History of Work on the German Naval Enigma | url = http://www.ellsbury.com/gne/gne-000.htm | publisher = The National Archives, Kew, Reference HW 25/1 | ref = {{harvid|Alexander|circa 1945}} | access-date = 15 November 2010 | archive-date = 17 February 2022 | archive-url = https://web.archive.org/web/20220217145825/http://www.ellsbury.com/gne/gne-000.htm | url-status = live }}
* {{cite book |last=Beavers |first=Anthony |editor1-first=S. Barry |editor1-last=Cooper |editor2-first=Jan |editor2-last=van Leeuwen |title=Alan Turing: His Work and Impact |publisher=Elsevier |location=Waltham |year=2013 |pages=481–485 |chapter=Alan Turing: Mathematical Mechanist |isbn=978-0-12-386980-7 |chapter-url=https://books.google.com/books?id=C9WQbm4ovFoC&pg=PA481 }}
* {{cite journal|last1=Church|first1=Alonzo|author-link=Alonzo Church|title=An Unsolvable Problem of Elementary Number Theory|journal=[[American Journal of Mathematics]]|volume=58|issue=2|year=1936|pages=345–363|issn=0002-9327|doi=10.2307/2371045|jstor=2371045}}
* {{Cite journal | last = Copeland | first = B. Jack | author-link = Jack Copeland | title = Colossus: Its Origins and Originators | journal=[[IEEE Annals of the History of Computing]] | volume = 26 | issue = 4 | pages = 38–45 | year = 2004a |doi = 10.1109/MAHC.2004.26 | s2cid = 20209254}}
* {{Cite book |editor-last = Copeland |editor-first = B. Jack| title = The Essential Turing | year = 2004b | publisher=Oxford University Press | location = Oxford | isbn = 978-0-19-825079-1 | oclc = 156728127}}
* {{Cite book | last = Copeland | first = B. Jack | title = Colossus: The secrets of Bletchley Park's code-breaking computers | year = 2006 | publisher=Oxford University Press | isbn = 978-0-19-284055-4}}
** {{Cite book | last = Hilton | first = Peter | author-link = Peter Hilton | year = 2006 | chapter = Living with Fish: Breaking Tunny in the Newmanry and Testery |title=Colussus}} in {{Harvnb|Copeland|2006|pp=189–203}}
* {{Cite book | last = Gannon | first = Paul | title = Colossus: Bletchley Park's Greatest Secret | place = London | publisher=Atlantic Books | orig-year = 2006 | year = 2007 | isbn = 978-1-84354-331-2}}
* {{cite book | last = Hodges | first = Andrew| author-link = Andrew Hodges | title = [[Alan Turing: The Enigma]] |location = London | publisher=Burnett Books | isbn = 978-0-09-152130-1 | year = 1983 }}
* {{Cite book | last = Leavitt | first = David | author-link = David Leavitt | year = 2007 | title = The man who knew too much: Alan Turing and the invention of the computer | publisher=Phoenix | isbn = 978-0-7538-2200-5}}
* {{Cite book | last = Lewin | first = Ronald | author-link = Ronald Lewin | title = Ultra Goes to War: The Secret Story | edition = Classic Penguin | series = Classic Military History | year = 1978 | publication-date = 2001 | publisher=Hutchinson & Co | location = London | isbn = 978-1-56649-231-7}}
* {{Cite web | last = Mahon | first = A. P. | title = The History of Hut Eight 1939–1945 | publisher = UK National Archives Reference HW 25/2 | year = 1945 | url = http://www.ellsbury.com/hut8/hut8-000.htm | access-date = 10 December 2009 | archive-date = 9 February 2022 | archive-url = https://web.archive.org/web/20220209012625/http://www.ellsbury.com/hut8/hut8-000.htm | url-status = live }}
* {{Cite book | editor-last = Oakley | editor-first = Brian | editor-link = Brian Oakley | title = The Bletchley Park War Diaries: July 1939&nbsp;– August 1945 | publisher=Wynne Press | year = 2006 | edition = 2.6}}
* {{Cite book | last = Sipser | first = Michael | title = Introduction to the Theory of Computation | publisher=PWS Publishing | isbn = 978-0-534-95097-2 | year = 2006}}
* {{Cite news | last = Turing | first = A. M. | year = 1937 | title = On Computable Numbers, with an Application to the Entscheidungsproblem | orig-year = Delivered to the Society November 1936 | periodical = Proceedings of the London Mathematical Society | series = 2 | volume = 42 | issue = 1 | pages = 230–65 | doi = 10.1112/plms/s2-42.1.230 | url = http://www.comlab.ox.ac.uk/activities/ieg/e-library/sources/tp2-ie.pdf | access-date = 15 July 2009 | archive-date = 6 May 2011 | archive-url = https://web.archive.org/web/20110506090827/http://www.comlab.ox.ac.uk/activities/ieg/e-library/sources/tp2-ie.pdf | url-status = live }}
{{Refend}}

==Further reading==
===Articles===
{{refbegin}}
* {{cite journal |title=The Mind and the Computing Machine: Alan Turing and others |journal=[[The Rutherford Journal]] |url=http://www.rutherfordjournal.org/article010111.html |editor-first=B. Jack |editor-last=Copeland |editor-link=Jack Copeland |access-date=6 April 2009 |archive-date=18 March 2012 |archive-url=https://web.archive.org/web/20120318165042/http://www.rutherfordjournal.org/article010111.html |url-status=live }}
* {{cite journal |title=Alan Turing: Father of the Modern Computer |journal=[[The Rutherford Journal]] |url=http://www.rutherfordjournal.org/article040101.html |editor-first=B. Jack |editor-last=Copeland |access-date=19 November 2013 |archive-date=24 January 2022 |archive-url=https://web.archive.org/web/20220124221719/http://rutherfordjournal.org/article040101.html |url-status=live }}
* {{cite ODNB|id=36578|title=Turing, Alan Mathison|year=2004|last=Hodges|first=Andrew}}
* {{cite encyclopaedia |last=Hodges |first=Andrew |editor=Edward N. Zalta |encyclopedia=[[Stanford Encyclopedia of Philosophy]] |title=Alan Turing |url=http://plato.stanford.edu/entries/turing/ |access-date=10 January 2011 |edition=Winter 2009 |year=2007 |publisher=[[Stanford University]] }}
* {{cite magazine|last=Gray|first=Paul|date=29 March 1999|title=Computer Scientist: Alan Turing|magazine=Time|url=http://www.time.com/time/magazine/article/0,9171,990624,00.html|archive-url=https://web.archive.org/web/20071016225903/http://www.time.com/time/magazine/article/0,9171,990624,00.html|url-status=dead|archive-date=16 October 2007}}
* {{Cite journal | last1 = O'Connell | first1 = H | last2 = Fitzgerald | first2 = M | title = Did Alan Turing have Asperger's syndrome? | journal=Irish Journal of Psychological Medicine | volume = 20 | issue = 1 | pages = 28–31 | publisher=Irish Institute of Psychological Medicine | year = 2003 | issn = 0790-9667 | doi=10.1017/s0790966700007503| pmid = 30440230 | s2cid = 53563123 }}
* {{MacTutor Biography|id=Turing|title=Alan Mathison Turing}}
{{refend}}

===Books===
{{refbegin}}
* {{Cite book | last = Agar | first = Jon | title = Turing and the Universal Machine | location = Duxford | publisher=Icon | year=2001 | isbn = 978-1-84046-250-0 }}
* {{Cite book | last = Agar | first = Jon | title = The government machine: a revolutionary history of the computer | publisher=MIT Press | year = 2003 | location = Cambridge, Massachusetts | isbn = 978-0-262-01202-7 }}
* {{cite book | last=Babbage | first=Charles | author-link = Charles Babbage | editor-last=Campbell-Kelly | editor-first=Martin | title=The Works of Charles Babbage: Passages from the Life of a Philosopher | publisher=Routledge | publication-place=Oxford | orig-date=1864 | date=2016 | isbn=978-1-138-76370-8}}
* {{Cite book | last = Beniger | first = James | author-link = James R. Beniger | title = The control revolution: technological and economic origins of the information society | publisher=Harvard University Press | year = 1986 | location = Cambridge, Massachusetts | isbn = 978-0-674-16986-9 | title-link = The control revolution: technological and economic origins of the information society }}
* {{Cite book |last= Bernhardt |first= Chris |title= Turing's Vision: The Birth of Computer Science |publisher= MIT Press |year= 2017 |isbn= 978-0-262-53351-5 }}
* {{Cite book | last = Bodanis | first = David | author-link = David Bodanis | title = Electric Universe: How Electricity Switched on the Modern World | year = 2005 |publisher=Three Rivers Press | location = New York | isbn = 978-0-307-33598-2 | oclc = 61684223}}
* {{Cite book | last = Bruderer |first = Herbert |title = Konrad Zuse und die Schweiz. Wer hat den Computer erfunden? |chapter = Die Maschinen von Charles Babbage, Alan Turing und John von Neumann | publisher =  Oldenbourg Wissenschaftsverlag |location = München | year = 2012 |isbn = 978-3-486-71366-4 | doi = 10.1524/9783486716658 | language = de}}
* {{Cite book | last1 = Campbell-Kelly | first1 = Martin | author-link = Martin Campbell-Kelly | last2 = Aspray | first2 = William | title = Computer: A History of the Information Machine | publisher = Basic Books | year = 1996 | location = New York | isbn = 978-0-465-02989-1 | url = https://archive.org/details/computerhistoryo00camp |url-access=registration}}
* {{Cite book | last = Ceruzzi | first = Paul E. | author-link = Paul E. Ceruzzi | title = A History of Modern Computing | publisher=MIT Press | year = 1998 | location = Cambridge, Massachusetts, and London | isbn = 978-0-262-53169-6}}
* {{Cite book | last = Chandler | first = Alfred | author-link = Alfred D. Chandler Jr. | title = The Visible Hand: The Managerial Revolution in American Business | publisher = Belknap Press | year = 1977 | location = Cambridge, Massachusetts | isbn = 978-0-674-94052-9 | url = https://archive.org/details/visiblehandmanag00chan|url-access=registration }}
* {{cite book | last1 = Cooper | first1 = S. Barry | last2 = van Leeuwen | first2 = Jan | title = Alan Turing: His Work and Impact | year = 2013 | location = New York | publisher = Elsevier | isbn = 978-0-12-386980-7}}
* {{Cite book | editor-link=Jack Copeland | editor-last = Copeland | editor-first = B. Jack | title = Alan Turing's Automatic Computing Engine | year = 2005 | publisher = Oxford University Press | location = Oxford | isbn = 978-0-19-856593-2 | oclc = 224640979 | url = https://archive.org/details/alanturingsautom0000unse |url-access=registration}}
* {{cite book| last1=Copeland |first1=B. Jack | author-link2=Jonathan Bowen | last2=Bowen | first2=Jonathan P. | author-link3=Robin Wilson (mathematician) | last3=Wilson | first3=Robin | last4=Sprevak | first4=Mark | title=The Turing Guide | publisher=[[Oxford University Press]] | date=2017 | isbn=978-0-19-874783-3 | title-link=The Turing Guide }}
* {{cite book| title=Turing's Cathedral: The Origins of the Digital Universe | author-link=George Dyson (science historian) | first=George | last=Dyson | isbn=978-1-4000-7599-7 | year=2012 | publisher=Vintage }}
* {{Cite book | last = Edwards | first = Paul N | title = The closed world: computers and the politics of discourse in Cold War America | publisher=MIT Press | year = 1996 | location = Cambridge, Massachusetts | isbn = 978-0-262-55028-4 }}
* {{cite book| author-link=James Gleick | last=Gleick | first=James | title=The Information: A History, a Theory, a Flood | location=New York | publisher=Pantheon | date=2011 | isbn=978-0-375-42372-7 | title-link=The Information: A History, a Theory, a Flood }}
* {{Cite book | last = Hochhuth | first = Rolf | author-link = Rolf Hochhuth | title = Alan Turing: en berättelse | publisher=Symposion | year = 1988 | isbn = 978-91-7868-109-9 }}
* {{cite book| title=Alan Turing: The Enigma| year=2014 | first=Andrew | last=Hodges | author-link=Andrew Hodges | publisher=[[Princeton University Press]] | isbn=978-0-691-16472-4 }} (originally published in 1983); basis of the film ''[[The Imitation Game]]''
* {{Cite book | last = Levin | first = Janna | author-link = Janna Levin | title = A Madman Dreams of Turing Machines | publisher=Knopf | year = 2006 | location = New York | isbn = 978-1-4000-3240-2 }}
* {{Cite book | last = Lubar | first = Steven | year = 1993 | title = Infoculture | location = Boston, Massachusetts and New York | publisher = Houghton Mifflin | isbn = 978-0-395-57042-5 | url = https://archive.org/details/infoculturesmith00luba |url-access=registration}}
* {{Cite book |last=Petzold |first=Charles |year=2008 |title=[[The Annotated Turing]]: A Guided Tour through Alan Turing's Historic Paper on Computability and the Turing Machine |location=[[Indianapolis]] |publisher=Wiley Publishing |isbn=978-0-470-22905-7}}
* {{Cite book |last=Smith |first=Roger |year=1997 |title=Fontana History of the Human Sciences |location=London |publisher=Fontana}}
* {{Cite book | last = Turing | first = Sara Stoney | title = Alan M Turing | publisher=W Heffer | year = 1959}} Turing's mother, who survived him by many years, wrote this 157-page biography of her son, glorifying his life. It was published in 1959, and so could not cover his war work. Scarcely 300 copies were sold (Sara Turing to Lyn Newman, 1967, Library of [[St John's College, Cambridge]]). The six-page foreword by [[Lyn Irvine]] includes reminiscences and is more frequently quoted. It was re-published by Cambridge University Press in 2012, to honour the centenary of his birth, and included a new foreword by [[Martin Davis (mathematician)|Martin Davis]], as well as a never-before-published memoir by Turing's older brother John F. Turing.
* {{cite book | title=Alan M. Turing | year=2012 | first=Sara | last=Turing | publisher=[[Cambridge University Press]] | isbn=978-1-107-02058-0}} (originally published in 1959 by W. Heffer & Sons, Ltd)
* {{Cite book | last=Weizenbaum |first=Joseph |year=1976 |title=Computer Power and Human Reason |location=London |publisher=W.H. Freeman |isbn=0-7167-0463-3}}
* {{Cite book | last1 = Whitemore | first1 = Hugh | author-link = Hugh Whitemore | last2 = Hodges | first2 = Andrew | author-link2 = Andrew Hodges | title = Breaking the code | publisher=S. French | year = 1988}} This 1986 Hugh Whitemore play tells the story of Turing's life and death. In the original West End and Broadway runs, [[Derek Jacobi]] played Turing and he recreated the role in a 1997 television film based on the play made jointly by the BBC and [[WGBH-TV|WGBH, Boston]]. The play is published by Amber Lane Press, [[Oxford]], ASIN: B000B7TM0Q
* {{Cite book |last=Williams |first=Michael R. |year=1985 |title=A History of Computing Technology |location=[[Englewood Cliffs, New Jersey]] |publisher=[[Prentice-Hall]] |isbn=0-8186-7739-2}}
* {{Cite book|last=Yates |first=David M. |title=Turing's Legacy: A history of computing at the National Physical Laboratory 1945–1995 |year=1997 |publisher=[[Science Museum, London|London Science Museum]] |location=London |isbn=978-0-901805-94-2 |oclc=123794619}}
{{refend}}

==External links==
{{sister project links|wikt=n|commonscat=yes|b=n|v=n}}
* [http://purl.umn.edu/107493 Oral history interview with Nicholas C. Metropolis], [[Charles Babbage Institute]], University of Minnesota. Metropolis was the first director of computing services at [[Los Alamos National Laboratory]]; topics include the relationship between Turing and [[John von Neumann]]
* [http://www.iwm.org.uk/history/how-alan-turing-cracked-the-enigma-code How Alan Turing Cracked The Enigma Code] Imperial War Museums
* [http://www.mathcomp.leeds.ac.uk/turing2012/ Alan Turing Year] {{Webarchive|url=https://web.archive.org/web/20190217215512/http://www.mathcomp.leeds.ac.uk/turing2012/ |date=17 February 2019 }}
* [http://cie2012.eu/ CiE 2012: Turing Centenary Conference]
* [https://makingscience.royalsociety.org/s/rs/people/fst00117605 Science in the Making]{{Webarchive |url= https://web.archive.org/web/20230404044604/https://makingscience.royalsociety.org/s/rs/people/fst00117605 |date=4 April 2023 }} Alan Turing's papers in the Royal Society's archives
* [http://www.turing.org.uk/ Alan Turing] site maintained by [[Andrew Hodges]] including a [https://web.archive.org/web/20180721235734/http://www.turing.org.uk/bio/part1.html short biography]
* [https://web.archive.org/web/20181012014022/http://www.alanturing.net/ AlanTuring.net&nbsp;– Turing Archive for the History of Computing] by [[Jack Copeland]]
* [https://turingarchive.kings.cam.ac.uk/ The Turing Digital Archive]&nbsp;– contains scans of some unpublished documents and material from the King's College, Cambridge archive
* [https://archiveshub.jisc.ac.uk/manchesteruniversity/data/gb133-tur/add Alan Turing Papers] – [[University of Manchester Library]], Manchester
* {{cite journal|last=Jones|first=G. James|date=11 December 2001|title=Alan Turing&nbsp;– Towards a Digital Mind: Part 1|journal=System Toolbox|publisher=The Binary Freedom Project|url=http://www.systemtoolbox.com/article.php?history_id=3|url-status=dead|archive-url=https://web.archive.org/web/20070803163318/http://www.systemtoolbox.com/article.php?history_id=3|archive-date=3 August 2007}}
* [https://web.archive.org/web/20160104203150/http://oldshirburnian.org.uk/wp-content/uploads/2015/09/TURING-Alan-Mathison.pdf Sherborne School Archives] – holds papers relating to Turing's time at Sherborne School
* [https://oldshirburnian.org.uk/alan-turing-and-the-nature-of-spirit/ Alan Turing and the ‘Nature of Spirit’] (Old Shirburnian Society)
* [https://oldshirburnian.org.uk/alan-turing/ Alan Turing OBE, PhD, FRS (1912-1954)] (Old Shirburnian Society)
* [https://openplaques.org/people/368 Alan Turing plaques] recorded on openplaques.org
* [https://www.newscientist.com/people/alan-turing/ Alan Turing] archive on New Scientist

{{Alan Turing}}
{{FRS 1951}}
{{Timelines of computing}}
{{Time 100: The Most Important People of the Century}}
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