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{{Infobox nukes|country_name=[[Empire of Japan]]|image_location=Japanese Empire (orthographic projection).svg|program_start=1940 (ended in 1945)|first_test=None|first_fusion=None|last_test=None|largest_yield=None|total_tests=None|peak_stockpile=None|current_stockpile=None|current_usable_stockpile=None|current_usable_stockpile_megatonnage=None|maximum_range=None}}{{Weapons of mass destruction}}

During [[World War II]], [[Empire of Japan|Japan]] had several programs exploring the use of [[nuclear fission]] for military technology, including [[nuclear reactor]]s and [[nuclear weapon]]s. Like the [[German_nuclear_program_during_World_War_II|similar wartime programs in Nazi Germany]], it was relatively small, suffered from an array of problems brought on by lack of resources and wartime disarray, and was ultimately unable to progress beyond the laboratory stage during the war. 

Today, Japan has no known nuclear weapons programs. It is a signatory in good standing of the [[Nuclear Non-Proliferation Treaty]] and has enacted [[Japan's non-nuclear weapons policy|domestic legal prohibitions against producing nuclear weapons]]. However, it is unique among non-nuclear weapons states in that it possesses a full [[nuclear fuel cycle]], as part of its [[nuclear energy in Japan|civilian nuclear energy industry]], and advanced developments in the industries necessary to make nuclear weapons. As a result, it is often cited as a primary example of a [[nuclear latency|latent or threshold nuclear state]], capable of developing weapons in a very short timespan should its government decide to do so.<ref>{{cite web|title=Nuclear Threat Initiative Country Spotlight: Japan |publisher=Nuclear Threat Initiative |url=https://www.nti.org/countries/japan/ |date=2022-10-12}}</ref>

==Background==

[[File:RIKEN building in Taisho period.JPG|thumb|[[The Institute of Physical and Chemical Research]] building in Taisho period]]

In 1934, [[Tohoku University]] professor Hikosaka Tadayoshi's "atomic physics theory" was released. Hikosaka pointed out the huge energy contained by nuclei and the possibility that both nuclear power generation and weapons could be created.<ref>{{Cite web |url=http://histclo.com/essay/war/ww2/air/gas/nuc/w2-nucj.html |title=World War II: Japanese Nuclear Weapons/Genshi Bakudan Program}}</ref> In December 1938, the German chemists [[Otto Hahn]] and [[Fritz Strassmann]] sent a manuscript to ''[[Die Naturwissenschaften|Naturwissenschaften]]'' reporting that they had detected the element [[barium]] after bombarding [[uranium]] with [[neutrons]];<ref>O. Hahn and F.&nbsp;Strassmann. ''Über den Nachweis und das Verhalten der bei der Bestrahlung des Urans mittels Neutronen entstehenden Erdalkalimetalle'' ("On the detection and characteristics of the alkaline earth metals formed by irradiation of uranium with neutrons"), ''Naturwissenschaften'' Volume&nbsp;27, Number&nbsp;1, 11–15 (1939). The authors were identified as being at the Kaiser-Wilhelm-Institut für Chemie, Berlin-Dahlem. Received 22 December 1938.</ref> simultaneously, they communicated these results to [[Lise Meitner]]. Meitner, and her nephew [[Otto Robert Frisch]], correctly interpreted these results as being [[nuclear fission]]<ref>{{Cite journal | last1 = Meitner | first1 = Lise | author-link = Lise Meitner | last2 = Frisch | first2 = O.R. | author2-link = Otto Frisch | title = Disintegration of Uranium by Neutrons: a New Type of Nuclear Reaction | journal = [[Nature (journal)|Nature]] | volume = 143 | issue = 3615 | pages = 239–240 | date = 11 February 1939 | url = http://www.nature.com/physics/looking-back/meitner/index.html | doi =  10.1038/143239a0| bibcode=1939Natur.143..239M| s2cid = 4113262 | url-access = subscription }} The paper is dated 16 January 1939. Meitner is identified as being at the Physical Institute, Academy of Sciences, Stockholm, and Frisch as being at the Institute of Theoretical Physics, University of Copenhagen.</ref> and Frisch confirmed this experimentally on 13 January 1939.<ref>{{Cite journal|last=Frisch |first=O.R. |author-link=Otto Frisch |title=Physical Evidence for the Division of Heavy Nuclei under Neutron Bombardment |journal=[[Nature (journal)|Nature]] |volume=143 |issue=3616 |page=276 |date=18 February 1939 |doi=10.1038/143276a0 |bibcode=1939Natur.143..276F |s2cid=4076376 |doi-access=free }} The paper is dated 17 January 1939, and the experiment was conducted on 13 January 1939—see [[Richard Rhodes]] ''[[The Making of the Atomic Bomb]]'' pp. 263, 268</ref> Physicists around the world immediately realized that [[Nuclear chain reaction|chain reactions]] could be produced and notified their governments of the possibility of developing nuclear weapons.

==World War II==

[[File:Masatoshi Okochi.JPG|thumb|left|upright|The third director of the [[RIKEN|RIKEN Institute]] [[Masatoshi Okochi]] submitted a report on "Possibility of Uranium Bomb Manufacturing" in May 1941.]]

The leading figure in the Japanese atomic program was [[Yoshio Nishina]], a close associate of [[Niels Bohr]] and a contemporary of [[Albert Einstein]].<ref name="uiuc">{{Cite web |url=http://mragheb.com/NPRE%20402%20ME%20405%20Nuclear%20Power%20Engineering/Japanese%20Nuclear%20Weapons%20Program.pdf |title=Chapter 3: Japanese Nuclear Weapons Program |last=Ragheb|first=Magdi |date=17 March 2014|access-date=3 May 2015}}</ref> Nishina had co-authored the [[Klein–Nishina formula]].<ref>{{cite journal |
doi=10.1007/BF01366453 |author1=Klein, O |author2=Nishina, Y |
title=Über die Streuung von Strahlung durch freie Elektronen nach der neuen relativistischen Quantendynamik von Dirac|journal=Z. Phys.|volume=52 |
issue=11–12 |year=1929|pages=853 and 869|bibcode = 1929ZPhy...52..853K |s2cid=123905506 }}</ref> Nishina had established his own Nuclear Research Laboratory to study [[Particle physics|high-energy physics]] in 1931 at [[RIKEN|RIKEN Institute]] (the Institute for Physical and Chemical Research), which had been established in 1917 in Tokyo to promote basic research.<ref>{{Cite web |url=http://www.riken.jp/engn/r-world/riken/history/zaidan/index.html |title=RIKEN &#124; About RIKEN &#124; History &#124; Private Research Foundation Period Corporation Period |access-date=2011-12-31 |archive-date=2013-03-09 |archive-url=https://web.archive.org/web/20130309142912/http://www.riken.jp/engn/r-world/riken/history/zaidan/index.html |url-status=dead }}</ref> Nishina had built his first {{convert|26|inch|adj=on}} [[cyclotron]] in 1936, and another {{convert|60|inch|adj=on}}, 220-ton cyclotron in 1937. In 1938 Japan also purchased a cyclotron from the [[University of California, Berkeley]].<ref name="uiuc"/>

[[File:RIKENFirstCyclotron.jpg|thumb|Dr. [[Yoshio Nishina]] completed this "small" [[cyclotron]] in 1937, the first cyclotron constructed outside the United States (and the second in the world).]]

Due to the German-Japanese alliance resulting from Germany's [[Four Year Plan]], Japan and its military had already been pursuing nuclear science to catch up to the West in nuclear technology. This allowed for Nishina to introduce quantum mechanics to Japan.<ref name="Grunden 2005 107–130">{{Cite journal|last1=Grunden|first1=Walter E.|last2=Walker|first2=Mark|last3=Yamazaki|first3=Masakatsu|date=2005|title=Wartime Nuclear Weapons Research in Germany and Japan|url=https://www.jstor.org/stable/3655253|journal=Osiris|volume=20|pages=107–130|doi=10.1086/649415 |jstor=3655253 |pmid=20503760 |s2cid=46599081 |issn=0369-7827|url-access=subscription}}</ref>

In 1939, Nishina recognized the military potential of nuclear fission, and was worried that the Americans were working on a nuclear weapon which might be used against Japan.

In August 1939, Hungarian-born physicists [[Leo Szilard]] and [[Eugene Wigner]] drafted the [[Einstein–Szilard letter]], which warned of the potential development of "extremely powerful bombs of a new type".<ref>Copied from Wikipedia article "[[Manhattan Project#Origins|Manhattan Project]]". See that article for references.</ref>
The United States started the investigations into fission weapons in the United States, which eventually evolved into the massive [[Manhattan Project]], and the laboratory from which Japan purchased a cyclotron became one of the major sites for weapons research.

[[File:RIKENSecondCyclotron.jpg|thumb|The second RIKEN cyclotron, completed in 1943]]

In the early summer of 1940, Nishina met Lieutenant-General [[Takeo Yasuda]] on a train. Yasuda was at the time director of the Army Aeronautical Department's Technical Research Institute. Nishina told Yasuda about the possibility of building nuclear weapons.<ref>{{cite book | last = Maas  | first = Ad |author2=James Hogg | title = Scientific Research In World War II | publisher = Taylor & Francis | year = 2008 | page = 195 | isbn = 978-0-7103-1340-9 }}</ref> However, the Japanese fission project did not formally begin until April 1941 when Yasuda acted on Army Minister [[Hideki Tōjō]]'s order to investigate the possibilities of nuclear weapons. Yasuda passed the order down the chain of command to Viscount [[Masatoshi Ōkōchi]], director of the RIKEN Institute, who in turn passed it to Nishina, whose Nuclear Research Laboratory by 1941 had over 100 researchers.<ref name=dahl279>{{cite book | last = Dahl  | first = Per F. | title = Heavy water and the wartime race for nuclear energy | publisher = CRC Press | year = 1999 | pages = 279–285 | isbn = 978-0-7503-0633-1 }}</ref>

=== B-Research ===
Meanwhile, the Imperial Japanese Navy's Technology Research Institute had been pursuing its own separate investigations, and had engaged professors from the Imperial University, Tokyo, for advice on nuclear weapons. Before the Attack on Pearl Harbor in 1941, Captain Yoji Ito of the Naval Technical Research Institution of Japan initiated a study that would allow for the Japanese Navy to use nuclear fission. After consulting with Professor Sagane at Tokyo Imperial University, his research showed that nuclear fission would be a potential power source for the Navy.<ref name="Grunden 2005 107–130"/>

This resulted in the formation of the Committee on Research in the Application of Nuclear Physics, chaired by Nishina, that met ten times between July 1942 and March 1943. After the Japanese Navy lost at Midway, Captain Ito proposed a new type of nuclear weapons development designated as "B-Research" (also called "Jin Project", {{langx|ja|仁計画}}, lit. "Nuclear Project") by the end of June 1942. By December, deep in the project, it became evident that while an atomic bomb was feasible in principle, "Japanese scientists believed that it would be difficult for even the United States to realize the application of atomic energy in time to influence the outcome of the war."<ref name="Grunden 2005 107–130"/>  This caused the Navy to lose interest and to concentrate instead on research into [[radar]].<ref name="dahl279" />

===Ni-Go Project===
In 1942 the Army was not discouraged, and soon after the Committee issued its report it set up an experimental project at RIKEN, the Ni-Go Project (lit. "The Second Project"). Its aim was to separate [[uranium-235]] by [[Uranium enrichment#Thermal diffusion|thermal diffusion]], ignoring alternative methods such as [[electromagnetic separation]], [[gaseous diffusion]], and [[Gas centrifuge|centrifugal separation]].

By spring 1944, the Nishina Project barely made any progress due to insufficient uranium hexafluoride for its Clusius tube. The previously provided uranium within the copper tube had corroded and the project was unable to separate U-235 isotopes.<ref name="Grunden 2005 107–130"/>

By February 1945, a small group of scientists had succeeded in producing a small amount of material in a rudimentary separator in the RIKEN complex—material which RIKEN's cyclotron indicated was ''not'' uranium-235. The separator project came to an end in March 1945, when the building housing it was destroyed by a fire caused by [[Bombing of Tokyo (10 March 1945)|the USAAF's ''Operation Meetinghouse'' raid on Tokyo]]. No attempt was made to build a [[Nuclear reactor|uranium pile]]; [[heavy water]] was unavailable, but Takeuchi Masa, who was in charge of Nishina's separator, calculated that light water would suffice if the uranium could be [[Enriched uranium|enriched]] to 5–10% uranium-235.<ref name="dahl279" />

While these experiments were in progress, the Army and Navy searched for uranium ore, in locations ranging from [[Fukushima Prefecture]] to Korea, China, and Burma.<ref name=dahl279/> The Japanese also requested materials from their German allies and {{convert|560|kg|abbr=on}} of unprocessed [[uranium oxide]] was dispatched to Japan in April 1945 aboard the submarine {{warship|German submarine|U-234||2}}, which however surrendered to US forces in the Atlantic following Germany's surrender. The uranium oxide was reportedly labeled as "U-235", which may have been a mislabeling of the submarine's name and its exact characteristics remain unknown; some sources believe that it was not weapons-grade material and was intended for use as a catalyst in the production of synthetic [[methanol]] to be used for aviation fuel.<ref name=Boyd>{{cite book | last =  Boyd | first = Carl |author2=Akihiko Yoshida | title = The Japanese Submarine Force and World War II | publisher = Naval Institute Press | year = 2002 | page = 164 | isbn = 978-1-55750-015-1}}</ref><ref name=scalia>{{cite book | last = Scalia  | first = Joseph M. | title = Germany's Last Mission to Japan: The Failed Voyage of U-234 | publisher = Naval Institute Press | year = 2000 | isbn = 978-1-55750-811-9 }}</ref>

The attack also effectively destroyed the Clusius tube and any chances of the Japanese producing an atomic bomb in time to influence the war in their favor and rival the West in nuclear weaponry.<ref name="Grunden 2005 107–130"/>

According to the historian Williams, "The same lack of sufficient high quality uranium that had impeded the German atomic project had also, as it turned out, obstructed Japanese attempts to make a bomb." This was the conclusion of the Manhattan Project Intelligence Group, who also reported Japan's nuclear physicists were just as good as those from other nations.<ref>{{cite book|last1=Williams|first1=Susan|title=Spies in the Congo|date=2016|publisher=Publicaffaris|location=New York|isbn=9781610396547|page=231}}</ref>

===F-Go Project===
In 1943, a different Japanese naval command began a nuclear research program, the F-Go Project (lit. "The F Project"), under [[Bunsaku Arakatsu]] at the [[Kyoto University|Imperial University]], Kyoto. Arakatsu had spent some years studying abroad including at the [[Cavendish Laboratory]] at Cambridge under [[Ernest Rutherford]] and at [[Berlin University]] under [[Albert Einstein]]. Next to Nishina, Arakatsu was the most notable nuclear physicist in Japan.<ref name=zeman>{{cite book | last = Zeman  | first = Zbynek |author1-link = Zbyněk Zeman|author2=Rainer Karlsch | title = Uranium Matters: Central European Uranium in International Politics, 1900-1960 | publisher = Central European University Press | year = 2008 | page = 15 | isbn = 978-963-9776-00-5 }}</ref> His team included [[Hideki Yukawa]], who would become in 1949 the first Japanese physicist to receive a [[Nobel Prize]].

Early on in the war Commander Kitagawa, head of the Navy Research Institute's Chemical Section, had requested Arakatsu to carry out work on the separation of Uranium-235. The work went slowly, but shortly before the end of the war he had designed an [[ultracentrifuge]] (to spin at 60,000 rpm) which he was hopeful would achieve the required results. Only the design of the machinery was completed before the Japanese surrender.<ref name=dahl279/><ref>{{cite book | last = Dees | first = Bowen C. | title = The Allied Occupation and Japan's Economic Miracle: Building the Foundations of Japanese Science and Technology 1945–52 | publisher = Routledge | year = 1997 | page = 96 | isbn = 978-1-873410-67-7}}
</ref>

[[File:拆除中的荒勝研究室加速器.png|thumb|left|[[Bunsaku Arakatsu]]'s [[particle accelerator|accelerator]] demolition by [[Supreme Commander for the Allied Powers|GHQ]], 24 November 1945.]]

After Arakatsu and Nishina's meeting, in spring 1944, the Army-Navy Technology Enforcement Committee formed due to lack of progress in the development of Japanese nuclear weapons. This led to the only meeting of the leaders of the F-Go Project scientists, on 21 July 1945. After the meeting, nuclear weaponry research ended as a result of the destruction of the facility that housed isotope separation research, known as Building&nbsp;49.<ref name="Grunden 2005 107–130"/>

Shortly after the surrender of Japan, the [[Manhattan Project]]'s Atomic Bomb Mission, which had deployed to Japan in September, reported that the F-Go Project had obtained 20&nbsp;grams a month of [[heavy water]] from electrolytic [[ammonia]] plants in Korea and [[Kyushu]]. In fact, the industrialist Jun Noguchi had launched a heavy water production program some years previously. In 1926, Noguchi founded the Korean Hydro Electric Company at Konan (now known as [[Hungnam]]) in north-eastern Korea: this became the site of an industrial complex producing ammonia for fertilizer production. However, despite the availability of a heavy-water production facility whose output could potentially have rivalled that of [[Norsk Hydro]] at [[Vemork]] in Norway, it appears that the Japanese did not carry out neutron-multiplication studies using heavy water as a [[Neutron moderator|moderator]] at Kyoto.<ref name="dahl279" />

===Postwar aftermath===
On 16 October 1945, Nishina sought permission from the American occupation forces to use the two [[cyclotron]]s at the Riken Institute for biological and medical research, which was soon granted; however, on 10 November instructions were received from the US Secretary of War in Washington to destroy the cyclotrons at the Riken, Kyoto University, and Osaka University.<ref>{{cite journal|author=Werner, Charles|title=Retroactive saber rattling?|journal=Bulletin of the Atomic Scientists|volume=34|issue=44|year=1978|pages=10–12|url=https://books.google.com/books?id=5goAAAAAMBAJ&pg=PA10|doi=10.1080/00963402.1978.11458486|bibcode=1978BuAtS..34d..10W |url-access=subscription}}</ref> This was done on 24 November; the Riken's cyclotrons were taken apart and thrown into Tokyo Bay.<ref name=maas198>Maas and Hogg, pp. 198-199</ref>

In a letter of protest against this destruction Nishina wrote that the cyclotrons at the Riken had had nothing to do with the production of nuclear weapons, however the large cyclotron had officially been a part of the Ni-Go Project. Nishina had placed it within the Project by suggesting that the cyclotron could serve basic research for the use of nuclear power, simply so that he could continue working on the device; the military nature of the Project gave him access to funding and kept his researchers from being drafted into the armed forces. He felt no qualms about this because he saw no possibility of producing nuclear weapons in Japan before the end of the war.<ref name=maas198/>

===Reports of a Japanese weapon test===
On 2 October 1946, the ''[[Atlanta Constitution]]'' published a story by reporter David Snell,<ref>{{Cite news|url=https://www.latimes.com/archives/la-xpm-1997-06-01-mn-64618-story.html|title=New Details Emerge About Japan's Wartime A-Bomb Program|last=Benke|first=Richard|date=June 1, 1997|work=Los Angeles Times|access-date=July 21, 2018|language=en-US}}</ref> who had been an investigator with the 24th Criminal Investigation Detachment in Korea after the war, which alleged that the Japanese had successfully tested a nuclear weapon near [[Hungnam]] (Konan) before the town was captured by the Soviets. He said that he had received his information at Seoul in September 1945 from a Japanese officer to whom he gave the pseudonym of Captain Wakabayashi, who had been in charge of counter-intelligence at Hungnam.<ref>{{Cite news | last = Snell | first = David | title =  Japan Developed Atom Bomb; Russia Grabbed Scientists | newspaper = [[Atlanta Constitution]] | date = 3 October 1946 }}</ref><ref name=dees2021>Dees, pp. 20-21</ref><ref>{{cite book | last = Maga | first = Timothy P. | title = Judgment at Tokyo: the Japanese War Crimes Trials | publisher = University Press of Kentucky| year = 2001 | pages = 51–52 | isbn = 978-0-8131-2177-2}}</ref> [[Supreme Commander of the Allied Powers|SCAP]] officials, who were responsible for strict censorship of all information about Japan's wartime interest in nuclear physics,<ref>"The Allied Occupation and Japan's Economic Miracle: Building the Foundations of Japanese Science and Technology 1945-52" pub 1997, by Bowen Causey Dees, pages 96-97</ref> were dismissive of Snell's report.

Under the 1947–1948 investigation, comments were sought from Japanese scientists who would or should have known about such a project. Further doubt is cast on Snell's story by the lack of evidence of large numbers of Japanese scientists leaving Japan for Korea and never returning.<ref name=dees2021/> Snell's statements were repeated by Robert K. Wilcox in his 1985 book ''Japan's Secret War: Japan's Race Against Time to Build Its Own Atomic Bomb''. The book also included what Wilcox stated was new evidence from intelligence material which indicated the Japanese might have had an atomic program at Hungnam.<ref>{{cite book | last = Wilcox | first = Robert K. | title = Japan's Secret War: Japan's Race Against Time to Build Its Own Atomic Bomb | publisher = William Morrow & Company | year = 1985 | isbn = 978-0-688-04188-5}}</ref> These specific reports were dismissed in a review of the book by [[United States Department of Energy|Department of Energy]] employee Roger M. Anders which was published in the journal ''Military Affairs'',<ref>{{Cite journal | last = Anders | first = Roger M. | title = Review of Japan's Secret War | journal = Military Affairs | volume = 50 | issue = 1 | date = January 1986 }}</ref> an article written by two historians of science in the journal ''Isis'',<ref>{{Cite journal | last1 = Home | first1 = R.W. | last2 = Low | first2 = Morris F. | title = Postwar Scientific Intelligence Missions to Japan | journal = Isis | volume = 84 | issue = 3 | pages = 527–537 | date = September 1993 | doi =  10.1086/356550| s2cid = 144114888 }}</ref> and another article in the journal ''Intelligence and National Security''.<ref>{{Cite journal | last = Grunden | first = Walter E. | title = Hungnam and the Japanese Atomic Bomb: Recent Historiography of a Postwar Myth | journal = Intelligence and National Security | volume = 13 | issue = 2 | pages = 32–60 | year = 1998  | doi =  10.1080/02684529808432475}}</ref>

==Postwar==
Since the bombing of Hiroshima and Nagasaki, Japan has been a staunch upholder of antinuclear sentiments. Its postwar [[Constitution of Japan|Constitution]] forbids the establishment of offensive military forces, and in 1967 it adopted the [[Three Non-Nuclear Principles]], ruling out the production, possession, or introduction of nuclear weapons. Despite this, the idea that Japan might become a nuclear power has persisted. After China's [[596 (nuclear test)|first nuclear test]] in 1964, Japanese Prime Minister [[Eisaku Satō]] said to President [[Lyndon Johnson]] when they met in January 1965, that if the Chinese Communists had nuclear weapons, the Japanese should also have them. This shocked Johnson's administration, especially when Sato added that "Japanese public opinion will not permit this at present, but I believe that the public, especially the younger generation, can be 'educated'."<ref name=campbell>{{cite book | last = Campbell | first = Kurt M. | author2 = Robert J. Einhorn | author3 = Mitchell Reiss | title = The Nuclear Tipping Point: Why States Reconsider Their Nuclear Choices | publisher = Brookings Institution Press | year = 2004 | pages = [https://archive.org/details/nucleartippingpo0000unse/page/228 228–230] | url = https://archive.org/details/nucleartippingpo0000unse/page/228 | isbn = 978-0-8157-1331-9 }}</ref>

Throughout Sato's administration Japan continued to discuss the nuclear option. It was suggested that [[tactical nuclear weapon]]s, as opposed to larger strategic weapons, could be defined as defensive, and therefore be allowed by the Japanese Constitution. A White Paper commissioned by future Prime Minister [[Yasuhiro Nakasone]] opined that it would be possible that possessing small-yield, purely defensive nuclear weapons would not violate the Constitution, but that in view of the danger of adverse foreign reaction and possible war, a policy would be followed of not acquiring nuclear weapons "at present".<ref name=campbell/>

===Nuclear Non-Proliferation Treaty===
The Johnson administration became anxious about Sato's intentions and made securing Japan's signature to the [[Nuclear Non-Proliferation Treaty]] (NPT) one of its top priorities. In December 1967, to reassure the Japanese public, Sato announced the adoption of the [[Three Non-Nuclear Principles]]. These were that Japan would not manufacture, possess, or permit nuclear weapons on Japanese soil. The principles, which were adopted by the Diet, but are not law, have remained the basis of Japan's nuclear policy ever since.<ref name=campbell/>

According to Kei Wakaizumi, one of Sato's policy advisers, Sato realized soon after making the declaration that it might be too constraining. He therefore clarified the principles in a February 1968 address to the Diet by declaring the "Four Nuclear Policies" ("Four-Pillars Nuclear Policy"):

* Promotion of the peaceful use of nuclear energy
* Efforts towards global nuclear disarmament
* Reliance and dependence on US extended deterrence, based on the 1960 US-Japan Security Treaty
* Support for the "Three Non-Nuclear Principles under the circumstances where Japan's national security is guaranteed by the other three policies."

It followed that if American assurance was ever removed or seemed unreliable, Japan might have no choice but to go nuclear. In other words, it kept the nuclear option available.<ref name=schell>{{cite book | last = Schell | first = Jonathan | author-link = Jonathan Schell | title = The Seventh Decade: The New Shape of Nuclear Danger | publisher = Macmillan | year = 2007 | page = [https://archive.org/details/seventhdecade00sche/page/145 145] | url = https://archive.org/details/seventhdecade00sche/page/145 | isbn = 978-0-8050-8129-9 | url-access = registration }}</ref>

In 1969, a policy planning study for Japan's Foreign Ministry concluded that Japan should, even if it signed the NPT, maintain the economic and technical ability to develop and produce nuclear weapons in case it should ever become necessary, for example due to the international situation.

Japan finally signed the NPT in 1970 and ratified it in 1976, but only after [[West Germany]] became a signatory and the US promised "not to interfere with Tokyo's pursuit of independent reprocessing capabilities in its civilian nuclear power program".<ref name=campbell/>

===Extension of Nuclear Non-Proliferation Treaty===
In 1995, the [[Presidency of Bill Clinton|Clinton administration]] pushed the Japanese government to endorse the indefinite extension of the NPT, but it opted for an ambiguous position on the issue. A former Japanese government official recalled, "We thought it was better for us not to declare that we will give up our nuclear option forever and ever". However, eventually pressure from Washington and other nations led to Japan's supporting the indefinite extension.<ref name=campbell/>

In 1998, two events strengthened the hand of those in Japan advocating that the nation should at least reconsider if not reverse its non-nuclear policy. Advocates of such policies included conservative academics, some government officials, a few industrialists, and nationalist groups.<ref name=campbell/>

The first of these events was [[Pokhran-II|India]] and [[Chagai-I|Pakistan]] both conducting nuclear tests; the Japanese were troubled by a perceived reluctance on the part of the international community to condemn the two countries' actions, since one of the reasons Japan had opted to join the NPT was that it had anticipated severe penalties for those states who defied the international consensus against further nuclear proliferation. Also, Japan and other nations feared that an Indian nuclear arsenal could cause a localized nuclear arms race with China.<ref name=campbell/>

The second event was the August 1998 launch of a North Korean [[Taepodong-1]] missile over Japan which caused a public outcry and led some to call for remilitarization or the development of nuclear weapons. [[Fukushiro Nukaga]], head of the [[Ministry of Defense (Japan)|Japan Defense Agency]], said that his government would be justified in mounting pre-emptive strikes against North Korean missile bases. Prime Minister [[Keizō Obuchi]] reiterated Japan's non-nuclear weapon principles and said that Japan would not possess a nuclear arsenal, and that the matter was not even worthy of discussion.

However, it is thought that Prime Minister [[Junichiro Koizumi]] implied he agreed that Japan had the right to possess nuclear weapons when he added, "it is significant that although we could have them, we don't".<ref name=campbell/>

Earlier, [[Shinzō Abe]] had said that Japan's constitution did not necessarily ban possession of nuclear weapons, so long as they were kept at a minimum and were tactical weapons, and Chief Cabinet Secretary [[Yasuo Fukuda]] had expressed a similar view.<ref name=schell/>

===De facto nuclear state===
{{See also|Nuclear latency}}
While there are currently no known plans in Japan to produce nuclear weapons, it has been argued Japan has the technology, raw materials, and the capital to produce nuclear weapons within one year if necessary, and many analysts consider it a ''de facto'' [[List of states with nuclear weapons|nuclear state]] for this reason.<ref>{{Cite web |url=http://www.largeassociates.com/R3126-A1-%20final.pdf |date=May 2, 2005 |author=John H. Large |title=The actual and potential development of Nuclear Weapons Technology in the area of North East Asia (Korean Peninsular and Japan) |archive-url=https://web.archive.org/web/20070710105632/http://www.largeassociates.com/R3126-A1-%20final.pdf |archive-date=2007-07-10 |id=R3126-A1}}</ref><ref name=tipping-point>{{cite book |pages=243–246 |url=https://books.google.com/books?id=NvkDBNV-ks8C |title=The Nuclear Tipping Point: Why States Reconsider Their Nuclear Choices |author1=Kurt M. Campbell |author2=Robert J. Einhorn |author3=Mitchell Reiss |publisher=Brookings Institution Press |year=2004 |isbn=9780815796596 |access-date=24 December 2013}}</ref> For this reason Japan is often said to be a "screwdriver's turn"<ref>{{cite web|title=Nuclear Scholars Initiative 2010: Recap of Seminar Four|url=http://csis.org/blog/nuclear-scholars-initiative-2010-recap-seminar-four|publisher=CSIS|access-date=29 June 2010|archive-date=7 August 2010|archive-url=https://web.archive.org/web/20100807143049/http://csis.org/blog/nuclear-scholars-initiative-2010-recap-seminar-four|url-status=dead}}</ref><ref>{{cite journal|last=Brumfiel|first=Geoff|title=Nuclear proliferation special: We have the technology|journal=Nature |date=November 2004|pages=432–7|issue=7016|volume=432|pmid=15565123|series=432-437|doi=10.1038/432432a|bibcode = 2004Natur.432..432B |s2cid=4354223|doi-access=free}}</ref> away from possessing nuclear weapons, or to possess a "bomb in the basement".<ref name=nbc-20140311>{{cite news |url=http://www.nbcnews.com/storyline/fukushima-anniversary/japan-has-nuclear-bomb-basement-china-isnt-happy-n48976 |title=Japan Has Nuclear 'Bomb in the Basement,' and China Isn't Happy |first=Robert|last=Windrem |publisher=NBC News |date=11 March 2014 |access-date=3 April 2015}}</ref>

The United States stored extensive nuclear assets in [[Okinawa prefecture]] when it was under [[United States Civil Administration of the Ryukyu Islands|American administration]] until the 1970s. There were approximately 1,200 nuclear warheads in Okinawa.<ref>{{cite news |title='Okinawa bacteria' toxic legacy crosses continents, spans generations |first=Jon |last=Mitchell |url=http://www.japantimes.co.jp/community/2013/06/04/issues/okinawa-bacteria-toxic-legacy-crosses-continents-spans-generations/ |newspaper=The Japan Times |date=June 4, 2013 |access-date=September 2, 2019 |archive-date=September 2, 2019 |archive-url=https://web.archive.org/web/20190902122922/https://www.japantimes.co.jp/community/2013/06/04/issues/okinawa-bacteria-toxic-legacy-crosses-continents-spans-generations/ |url-status=live }}</ref>

Significant amounts of [[reactor-grade plutonium]] are created as a by-product of the nuclear energy industry. During the 1970s, the Japanese government made several appeals to the United States to use reprocessed plutonium in forming a "plutonium economy" for peaceful commercial use. This began a significant debate within the Carter administration about the risk of proliferation associated with reprocessing while also acknowledging Japan's need for energy and right to the use of peaceful nuclear technology. Ultimately, an agreement was reached that allowed Japan to repurpose the byproducts of nuclear power-related activities; however their efforts regarding fast-breeding plutonium reactors were largely unsuccessful.<ref>{{cite web |url=http://nsarchive.gwu.edu/briefing-book/nuclear-vault/2017-06-08/japan-plutonium-overhang-origins-dangers-debated-us-officials| title=Japan Plutonium Overhang Origins and Dangers Debated by U.S. Officials| publisher=[[National Security Archive]]| date=8 June 2017}}</ref>

In 2012, Japan was reported to have 9 tonnes of plutonium stored in Japan, which would be enough for more than 1,000 nuclear warheads, and an additional 35 tonnes stored in Europe.<ref name=aca-20121101>{{cite web |url=http://www.armscontrol.org/act/2012_11/Strains-Seen-in-Japans-Plutonium-Policy |title=Strains Seen in Japan's Plutonium Policy |first=Daniel|last=Horner |publisher=Arms Control Association |date=November 2012 |access-date=23 December 2013}}</ref><ref name=wp-20120327>{{cite news |url=https://www.washingtonpost.com/world/asia_pacific/japan-has-lots-of-plutonium-on-hand-little-way-to-use-it/2012/03/27/gIQA7jjyeS_story.html |title=Japan has lots of plutonium on hand, little way to use it |first=Chico|last=Harlan |newspaper=Washington Post |date=27 March 2012 |access-date=23 December 2013}}</ref> It has constructed the [[Rokkasho Reprocessing Plant]], which could produce further plutonium.<ref name=aca-20121101/> Japan has a considerable quantity of [[highly enriched uranium]] (HEU), supplied by the U.S. and UK, for use in its [[research reactor]]s and [[fast neutron reactor]] research programs; approximately 1,200 to 1,400&nbsp;kg of HEU as of 2014.<ref name=nti-20140129>{{cite web |url=http://www.nti.org/analysis/articles/civilian-heu-japan/ |title=Civilian HEU: Japan |publisher=Nuclear Threat Initiative |date=29 January 2014 |access-date=9 March 2014}}</ref> Japan also possesses an indigenous [[uranium enrichment]] plant<ref name=tipping-point/><ref name=jnfl-enrichment>{{cite web |url=http://www.jnfl.co.jp/english/uranium.html |title=Our Business - Uranium Enrichment |publisher=Japan Nuclear Fuel Limited |archive-url=https://web.archive.org/web/20070702173839/http://www.jnfl.co.jp/english/uranium.html |archive-date=2 July 2007}}</ref> which could hypothetically be used to make highly enriched uranium suitable for weapons use.

Japan has also developed the [[M-V]] three-stage [[solid-fuel rocket]], somewhat similar in design to the U.S. [[LGM-118A Peacekeeper]] [[ICBM]], giving it a missile technology base. It now has an easier-to-launch second generation solid-fuel rocket, [[Epsilon (rocket)|Epsilon]]. Japan has experience in re-entry vehicle technology ([[OREX]], [[HOPE-X]]). Toshiyuki Shikata, a [[Tokyo Metropolitan Government]] adviser and former lieutenant general, said that part of the rationale for the fifth M-V [[Hayabusa]] mission, from 2003 to 2010, was that the re-entry and landing of its return capsule demonstrated "that Japan's ballistic missile capability is credible."<ref name=wsj-20111028>{{cite news |url=https://www.wsj.com/articles/SB10001424052970203658804576638392537430156 |title=In Japan, Provocative Case for Staying Nuclear |first=Chester|last=Dawson |newspaper=Wall Street Journal |date=28 October 2011 |access-date=13 November 2011 |archive-url=https://web.archive.org/web/20200810124901/https://www.wsj.com/articles/SB10001424052970203658804576638392537430156 |archive-date=August 10, 2020}}</ref> A Japanese [[Deterrence theory|nuclear deterrent]] would probably be sea-based with [[ballistic missile submarine]]s.<ref name="jpnbld">{{cite web |title=Would Japan Quickly Build Nuclear Weapons in a Crisis? |author=Kyle Mizokami |date=August 20, 2021 |url=https://nationalinterest.org/blog/reboot/would-japan-quickly-build-nuclear-weapons-crisis-192110 |archive-url=https://web.archive.org/web/20210820093315/https://nationalinterest.org/blog/reboot/would-japan-quickly-build-nuclear-weapons-crisis-192110 |archive-date=August 20, 2021}}</ref> In 2011, former Minister of Defense [[Shigeru Ishiba]] explicitly backed the idea of Japan maintaining the capability of [[nuclear latency]]:
{{blockquote|"I don't think Japan needs to possess nuclear weapons, but it's important to maintain our commercial reactors because it would allow us to produce a nuclear warhead in a short amount of time{{nbsp}}... It's a tacit nuclear deterrent"<ref name=wsj-20111028/>}}

On 24 March 2014, Japan agreed to turn over more than {{convert|700|lb}} of weapons grade plutonium and highly enriched uranium to the US,<ref>{{cite web |url=http://america.aljazeera.com/articles/2014/3/24/japan-to-turn-overnuclearmaterialtous.html |title=Japan to turn over nuclear material to US |date=24 March 2014 |publisher=The Associated Press |access-date=24 March 2014}}</ref> which started to be returned in 2016.<ref name=jt-20160306>{{cite news |url=http://www.japantimes.co.jp/news/2016/03/06/national/ships-prepare-return-331-kg-plutonium-stash-japan-u-s/ |title=Ships prepare to return 331-kg plutonium stash from Japan to U.S. |newspaper=The Japan Times |date=6 March 2016 |access-date=12 March 2016 |archive-date=2 June 2022 |archive-url=https://web.archive.org/web/20220602000838/https://www.japantimes.co.jp/news/2016/03/06/national/ships-prepare-return-331-kg-plutonium-stash-japan-u-s/ |url-status=dead }}</ref> It has been pointed out that as long as Japan enjoys the benefits of a "nuclear-ready" status held through surrounding countries, it will see no reason to actually produce nuclear arms, since by remaining below the threshold, although with the capability to cross it at short notice, Japan can expect the support of the US while posing as an equal to China and Russia.<ref>{{cite book | last = Park| first = Tong Whan | title = The U.S. and the Two Koreas: A New Triangle | publisher = Lynne Rienner Publishers | year = 1998 | page = 111 | isbn = 978-1-55587-807-8}}</ref>

Former Mayor and Governor of Osaka [[Tōru Hashimoto]] in 2008 argued on several television programs that Japan should possess nuclear weapons, but has since said that this was his private opinion.<ref>''Japan Times'' [http://www.japantimes.co.jp/text/fl20121030lg.html The world according to Toru Hashimoto 30 October 2012] {{Webarchive|url=https://web.archive.org/web/20130103115738/http://www.japantimes.co.jp/text/fl20121030lg.html |date=3 January 2013 }}</ref>

Former Governor of Tokyo 1999-2012, [[Shintaro Ishihara]] was an advocate of Japan having nuclear weapons.<ref>Herman, Steve (15 February 2013) [https://www.voanews.com/a/rising-voices-in-south-korea-japan-advocate-nuclear-weapons/1604309.html "Rising Voices in S. Korea, Japan Advocate Nuclear Weapons."]. Voanews.com. Retrieved on 11 May 2014.</ref>

On 29 March 2016, then-U.S. presidential candidate [[Donald Trump]] suggested that Japan should develop its own nuclear weapons, claiming that it was becoming too expensive for the US to continue to protect Japan from countries such as China, North Korea, and Russia that already have their own nuclear weapons.<ref name=Japan-Need-Nukes>{{cite web |url=https://www.cbsnews.com/news/donald-trump-japan-south-korea-might-need-nuclear-weapons/ |title=Donald Trump: Japan, South Korea might need nuclear weapons |publisher=CBS News |date=29 March 2016 |access-date=23 June 2019|archive-url=https://web.archive.org/web/20190611080231/https://www.cbsnews.com/news/donald-trump-japan-south-korea-might-need-nuclear-weapons/ |archive-date=11 June 2019}}</ref>

On 27 February 2022, former prime minister [[Shinzo Abe]] proposed that Japan should consider a [[nuclear sharing]] arrangement with the US similar to [[NATO]].<ref name="wsj-2022"/> This includes housing American nuclear weapons on Japanese soil for deterrence.<ref name="wsj-2022"/> This plan comes in the wake of the [[2022 Russian invasion of Ukraine]].<ref name="wsj-2022">{{cite web |title=A New Nuclear Debate in Japan |website=The Wall Street Journal |date=March 1, 2022 |url=https://www.wsj.com/articles/a-new-nuclear-debate-in-japan-shinzo-abe-nato-us-russia-ukraine-vladimir-putin-china-xi-jinping-11646147202 |archive-url=https://web.archive.org/web/20220316104830/https://www.wsj.com/articles/a-new-nuclear-debate-in-japan-shinzo-abe-nato-us-russia-ukraine-vladimir-putin-china-xi-jinping-11646147202 |archive-date=March 16, 2022}}</ref><ref name="bbc-2022"/> Many Japanese politicians consider [[Vladimir Putin]]'s threat to use nuclear weapons against a non-nuclear state to be a game changer.<ref name="bbc-2022">{{cite web |title=Will Ukraine invasion push Japan to go nuclear? |website=BBC |date=March 27, 2022 |url=https://www.bbc.com/news/world-asia-60857346 |archive-url=https://web.archive.org/web/20220326000643/https://www.bbc.com/news/world-asia-60857346 |archive-date=March 26, 2022}}</ref>

Although an indigenous nuclear program in Japan is unlikely to develop due to low public support, the existential Chinese and North Korean threats have raised security concerns domestically.<ref>{{Cite book |last=Toehrig |first=Terence |url=http://worldcat.org/oclc/1074343427 |title=Japan, South Korea, and the United States Nuclear Umbrella: Deterrence After the Cold War |date=19 September 2017 |isbn=978-0-231-52783-5 |oclc=1074343427}}</ref> The role of public opinion is central, and studies show that threat perceptions—mainly of China’s growing military abilities—have strengthened Japanese public support for a nuclear program.<ref>{{Cite journal |last=Machida |first=Satoshi |date=2014-05-02 |title=Who Supports Nuclear Armament in Japan? Threat Perceptions and Japan's Nuclear Armament |url=http://dx.doi.org/10.1080/02185377.2014.913492 |journal=Asian Journal of Political Science |volume=22 |issue=2 |pages=128–146 |doi=10.1080/02185377.2014.913492 |s2cid=154256610 |issn=0218-5377|url-access=subscription }}</ref> Japan has long held negative views on nuclear weapons, and previously, even discussions of nuclear armament or deterrence in the country was unpopular due to a strong "[[nuclear taboo]]".<ref>{{Cite web |last=Diaz-Maurin |first=François |date=2022-08-24 |title=The legacy of Shinzo Abe: a Japan divided about nuclear weapons |url=https://thebulletin.org/2022/08/the-legacy-of-shinzo-abe-a-japan-divided-about-nuclear-weapons/ |access-date=2022-12-09 |website=Bulletin of the Atomic Scientists |language=en-US}}</ref> However, this taboo has been breaking, especially because Abe elevated the topic to mainstream politics during his tenure.<ref>{{Cite web |last=Diaz-Maurin |first=François |date=2022-08-24 |title=The legacy of Shinzo Abe: a Japan divided about nuclear weapons |url=https://thebulletin.org/2022/08/the-legacy-of-shinzo-abe-a-japan-divided-about-nuclear-weapons/ |access-date=2022-12-09 |website=Bulletin of the Atomic Scientists |language=en-US}}</ref>

National identity is an important factor in Japanese nuclear armament. Since World War II, the peace constitution has greatly limited the ability of Japanese military advancement, restricting them from having an active military or waging war with another country.<ref>{{Cite journal |last=Ryu |first=Yongwook |date=2018-04-18 |title=To revise or not to revise: the 'peace constitution', pro-revision movement, and Japan's national identity |url=http://dx.doi.org/10.1080/09512748.2017.1408673 |journal=The Pacific Review |volume=31 |issue=5 |pages=655–672 |doi=10.1080/09512748.2017.1408673 |s2cid=158061505 |issn=0951-2748|url-access=subscription }}</ref> These restrictions and the strong desire of former colonies—especially Korea and China—for apology and reconciliation by Japan for its crimes and atrocities committed under pre-WWII imperialism, coupled with Japan's refusal to make appropriate amends,<ref>{{Cite book |last=Lind |first=Jennifer M. |url=http://worldcat.org/oclc/913071539 |title=Sorry states : apologies in international politics |date=2010 |publisher=Cornell University Press |isbn=978-0-8014-7628-0 |oclc=913071539}}</ref> led to the rise of a conservative branch of the ruling Liberal Democratic Party (LDP) in Japan that encouraged revisions to the Peace Constitution and promoted, under former prime minister Shinzo Abe, "healthy nationalism", which aimed to restore the Japanese public's sense of pride in the country.<ref>{{Citation |title=Leadership and nationalism: assessing Shinzo Abe |date=2015-12-22 |url=http://dx.doi.org/10.4324/9781315739601-16 |work=Asian Nationalisms Reconsidered |pages=99–107 |publisher=Routledge |doi=10.4324/9781315739601-16 |isbn=978-1-315-73960-1 |access-date=2022-12-09|url-access=subscription }}</ref> The revisionists sought to "create a new national identity" that increased national pride, allowed for collective self-defense and removed "institutional limitations on military activities".<ref>{{Cite journal |last=Ryu |first=Yongwook |date=2018-04-18 |title=To revise or not to revise: the 'peace constitution', pro-revision movement, and Japan's national identity |url=http://dx.doi.org/10.1080/09512748.2017.1408673 |journal=The Pacific Review |volume=31 |issue=5 |pages=655–672 |doi=10.1080/09512748.2017.1408673 |s2cid=158061505 |issn=0951-2748|url-access=subscription }}</ref>

Since the reliability of U.S. security guarantees shapes Japan's nuclear policy,<ref>{{Cite journal |last1=Debs |first1=Alexandre |last2=Monteiro |first2=Nuno P. |date=2018-01-02 |title=Cascading Chaos in Nuclear Northeast Asia |url=http://dx.doi.org/10.1080/0163660x.2018.1445902 |journal=The Washington Quarterly |volume=41 |issue=1 |pages=97–113 |doi=10.1080/0163660x.2018.1445902 |s2cid=158864458 |issn=0163-660X|url-access=subscription }}</ref> a strong American nuclear umbrella is necessary to prevent Japan from developing nuclear weapons of its own. Since the 1960s, however, Japanese confidence in U.S. security guarantees has been influenced by American foreign policy shifts, from Nixon's "Guam Doctrine" to Trump's desire for allies to provide more of their own security.<ref>{{Cite journal |last1=Debs |first1=Alexandre |last2=Monteiro |first2=Nuno P. |date=2018-01-02 |title=Cascading Chaos in Nuclear Northeast Asia |url=http://dx.doi.org/10.1080/0163660x.2018.1445902 |journal=The Washington Quarterly |volume=41 |issue=1 |pages=97–113 |doi=10.1080/0163660x.2018.1445902 |s2cid=158864458 |issn=0163-660X|url-access=subscription }}</ref><ref>{{Cite news |last=Terry |first=Sue Mi |date=2022-05-12 |title=North Korea's Nuclear Family |language=en-US |url=https://www.foreignaffairs.com/articles/north-korea/2021-08-24/north-koreas-nuclear-family |access-date=2022-12-09 |issn=0015-7120}}</ref> Although Japan developing nuclear weapons would violate the Non-Proliferation Treaty (NPT) and potentially decrease U.S. power in East Asia, there is historical precedent for the U.S. to be complacent regarding Japan building nuclear arms: as long as Japan is a democracy, a friend of Washington and has high state capacity, the U.S. alliance would likely be maintained.<ref>{{Cite web |last=Kelly |first=Robert E. |title=The U.S. Should Get Out of the Way in East Asia's Nuclear Debates |url=https://foreignpolicy.com/2022/07/15/us-south-korea-japan-east-asia-nuclear-debates-nonproliferation/ |access-date=2022-12-09 |website=Foreign Policy |language=en-US}}</ref> This was the case for France and the United Kingdom, when they developed their own nuclear weapons after the end of the Second World War despite American deterrence.<ref>{{Cite web |last=Kelly |first=Robert E. |title=The U.S. Should Get Out of the Way in East Asia's Nuclear Debates |url=https://foreignpolicy.com/2022/07/15/us-south-korea-japan-east-asia-nuclear-debates-nonproliferation/ |access-date=2022-12-09 |website=Foreign Policy |language=en-US}}</ref>

==See also==
*[[History of nuclear weapons]]
*[[Japan and weapons of mass destruction]]
*[[Japan's non-nuclear weapons policy]]
*[[German nuclear weapons program]]
*[[Nuclear latency]]

==References==
{{Reflist|30em}}

==Further reading==
*{{cite book |last=Grunden |first=Walter E. |title=Secret Weapons & World War II: Japan in the Shadow of Big Science |location=Lawrence |publisher=University Press of Kansas |year=2005 }}
*{{cite journal |first=Fintan |last=Hoey |year=2021 |doi=10.1080/07341512.2021.1882126 |title=The 'Conceit of Controllability': Nuclear Diplomacy, Japan's Plutonium Reprocessing Ambitions and US Proliferation Fears, 1974–1978 |journal=History and Technology |volume=37 |issue=1 |pages=44–66 |s2cid=234814470 }}
*{{cite journal |last=Ito |first=Kenji |year=2021 |doi=10.1080/07341512.2021.1897963 |title=Three tons of uranium from the International Atomic Energy Agency: diplomacy over nuclear fuel for the Japan Research Reactor-3 at the Board of Governors' meetings, 1958–1959 |journal=History and Technology |volume=37 |issue=1 |pages=67–89 |s2cid=235598893 }}
*{{cite book |last=Rhodes |first=Richard |title=[[The Making of the Atomic Bomb]] |location=New York |publisher=Simon and Schuster |year=1986 |isbn= }}

==External links==
*[https://web.archive.org/web/20160805013800/http://alsos.wlu.edu/qsearch.aspx?browse=warfare%2FJapanese%20Atomic%20Bomb%20Project Annotated bibliography of Japanese atomic bomb program from the Alsos Digital Library for Nuclear Issues.]
*[https://fas.org/nuke/guide/japan/nuke/ FAS: Nuclear Weapons Program: Japan]—[[Federation of American Scientists]]
*[https://web.archive.org/web/20061114054323/http://store.aetv.com/html/product/index.jhtml?id=74425 Japan's atomic bomb] History Channel International documentary
*[http://www.worldwar-two.net/events/japanese_nuclear_weapons_program/ Japanese Nuclear Weapons Program during the WWII]
*[http://nsarchive.gwu.edu/briefing-book/nuclear-vault/2017-06-08/japan-plutonium-overhang-origins-dangers-debated-us-officials Japan Plutonium Overhang Origins and Dangers Debated by U.S. Officials], published by the [[National Security Archive]]

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[[Category:Nuclear weapons programs]]
[[Category:Nuclear history of Japan]]
[[Category:Military history of Japan during World War II]]
[[Category:Military history of Japan]]
[[Category:Nuclear technology in Japan]]