View source for Unit 9420

{{Short description|Disease Research Unit of Japanese Army}}
{{Use dmy dates|date=November 2019}}
{{Coord|1|16|49.5|N|103|50|1.1|E|display=title}}
{{Infobox military unit
| unit_name                     = Unit Oka 9420
| native_name                   = {{lang|ja|岡9420部隊}}<br>
{{lang|ja| 南方軍防疫給水部}}
| image                         = King_Edward_VII_College_of_Medicine,_opened_on_15_February_1926_by_Governor_of_the_Straits_Settlements,_Sir_Laurence_Nunns_Guillemard.jpg
| caption                       = Singapore Headquarters of Unit 9420
| dates                         = 1942-1945
| country                       = {{JPN|1870}}
| branch                        = 
| role                          = 
| size                          = 
| command_structure             = 
| garrison                      = King Edward VII College of Medicine, Singapore
| battles                       = {{tree list}}
*[[Second Sino-Japanese War]]
**[[Battle of the Yunnan–Burma Road]]
*[[Pacific War]]
**[[Invasion of Buka and Bougainville]]
**[[Fu-Go balloon bomb]]
{{tree list/end}}
}}

{{nihongo|'''Unit Oka 9420'''|岡9420部隊|Oka 9420 Butai|lead=yes}}, also known as the {{nihongo|'''Epidemic Prevention and Water Purification Department of the Southern Expeditionary Army Group'''|南方軍防疫供水部|Nanpōgun Bōeki Kyūsui-bu}}, was a [[Epidemic Prevention and Water Purification Department|disease research unit]] within the [[Japan Ground Self-Defense Force|Japanese army]]. Founded in Nanjing, China in 1942 and headquartered in [[Japanese occupation of Singapore|Japanese-occupied Singapore]],<ref name=":8" />{{Rp|25–27}} the unit had branches in [[British Malaya|Malaya]], [[Dutch East Indies|Indonesia]], the [[History of the Philippines (1898–1946)|Philippines]], [[Papua New Guinea]], [[Thailand]], and [[Myanmar|Burma]], and participated in [[Biological warfare|bacteriological weapons]] attacks in northern Burma, Yunnan, China, and Papua New Guinea.<ref name=":7" /> With a suitable, tropical climate as a suitable bed for the breeding of rat fleas, Malaya was the largest rat flea farms outside of Japan and China during World War II. The unit left Singapore in mid-1945 and dissolved in 1946.<ref name=":7" />

== History ==
In January 1942, the [[Fourteenth Area Army|Fourteenth Army]] of the Japanese [[Southern Expeditionary Army Group]] captured [[Manila]], forcing American troops to retreat to the [[Bataan Peninsula]]. By early February, the initial Japanese assault on the Bataan Peninsula was unsuccessful. Subsequently, the Japanese command contemplated a biological attack utilising plague bombs from [[Tokyo]] and [[Kwantung Army]]. The [[Ministry of Agriculture, Forestry and Fisheries (Japan)|Ministry of Agriculture and Forestry]] thus began organising rat breeding in the [[Prefectures of Japan|Japanese prefectures]] of [[Ibaraki Prefecture|Ibaraki]], [[Tochigi Prefecture|Tochigi]], and [[Chiba Prefecture|Chiba]]. However, following the [[Battle of Bataan|fall of the Bataan Peninsula]] in April, the germ warfare plan was ultimately scrapped.<ref name=":8">{{Cite book |last=Zhang |first=Hua |title=Japanese Army 9420th Unit & Bacteriological Warfare in Yunnan |publisher=China Social Sciences Press |year=2018 |isbn=978-7-5203-2419-9 |location=Beijing |language=zh}}</ref>{{Rp|42–43}}

In early 1942, the Japanese military established the pioneer team of the [[Epidemic Prevention and Water Purification Department]] of the Southern Expeditionary Army Group in Nanjing, China. Following its formation by 26 March, the team left China via Shanghai, Taiwan and Manila and arrived in Singapore by 20 June. The unit was initially given the secret code "Oka" ({{Langx|ja|岡}}), as this was the secret code for the [[Seventh Area Army]]. Following a transfer of control to the [[Southern Expeditionary Army Group|Southern Expeditionary Army]], the unit also used the secret code for the army, "Joyo" ({{Langx|ja|威}}).<ref name=":8" />{{Rp|25–27}}

Commanded by Major General [[Kitagawa Masataka]], with [[Ryōichi Naitō]] as its director,<ref name=":1">{{Cite web |last=Tong |first=Billy |date=2020-09-03 |title=生化戰：岡字 9420 部隊 |url=https://www.cup.com.hk/2020/09/04/unit-oka-9420/ |archive-url=https://web.archive.org/web/20220827034522/https://www.cup.com.hk/2020/09/04/unit-oka-9420/ |archive-date=2022-08-27 |access-date=2024-02-20 |website=CUP Media |language=zh-hant}}</ref> the unit consisted of two teams, including one team, the Umeoka Unit, specialised for studying [[bubonic plague]] and the other, the Kono Unit, focusing on [[malaria]].<ref>{{Cite book |last=Gold |first=Hal |url=https://books.google.com/books?id=SC8OU1qLcW0C |title=Unit 731: Testimony |date=1996 |publisher=Yenbooks |isbn=978-4-900737-39-6 |pages=155–156 |language=en |chapter= |access-date=2024-02-21 |archive-url=https://web.archive.org/web/20220625034516/https://books.google.com/books?id=SC8OU1qLcW0C&newbks=0&hl=en |archive-date=2022-06-25 }}</ref><ref>{{Cite book |last=K. |first=David |title=Japan's dark background 1881-1945: Singapore- Headquarters of the Oka Unit (Unit 9420) |date= }}</ref> The stated mission of Unit 9420 was ostensibly to address local infectious disease issues, which attracted local elites such as Othman Wok, who was one of the founding father of the Republic of Singapore in the 1960s.<ref name=":1" /> During the Japanese occupation, Dr. [[J. M. J. Supramaniam]] was also forced to work with Unit 9420 but secretly smuggled medical supplies to needy prisoners of war and hospitals.<ref>{{Cite news |last=Ng |first=Wei Kai |date=2022-02-13 |title=Doctor tapped 2 books to maintain hope and faith during Japanese Occupation |url=https://www.straitstimes.com/singapore/parenting-education/doctor-tapped-2-books-to-maintain-hope-and-faith-during-japanese-occupation |archive-url=https://web.archive.org/web/20221127072620/https://www.straitstimes.com/singapore/parenting-education/doctor-tapped-2-books-to-maintain-hope-and-faith-during-japanese-occupation |archive-date=2022-11-27 |accessdate=2024-02-21 |newspaper=The Straits Times |language=en |issn=0585-3923 }}</ref>

As the only biochemical unit established outside of Japan, the all members of the unit came from Nanjing's [[Unit Ei 1644|Unit 1644]], but some were directly sent from Japan.<ref name=":8" />{{Rp|27–28}} The unit roster indicates that the number of Japanese personnel working in the unit increased from 146 in May 1942 to 862 by the beginning of 1945, including doctors, virologists, nurses, and others.<ref>{{Cite web |last= |date=2022-07-13 |title=Evidence confirms germ warfare and more by Japanese Unit 731 |url=https://global.chinadaily.com.cn/a/202207/13/WS62cd34f2a310fd2b29e6be75_5.html |archive-url=https://web.archive.org/web/20231208040223/https://global.chinadaily.com.cn/a/202207/13/WS62cd34f2a310fd2b29e6be75_5.html |archive-date=2023-12-08 |access-date=2024-02-21 |website=China Daily |language=en }}</ref><ref name=":4">{{Cite news |last=Zaccheus |first=Melody |last2= |first2= |date=2019-03-26 |title=WWII video points to secret bio warfare studies in Singapore |url=https://www.straitstimes.com/singapore/wwii-video-points-to-secret-bio-warfare-studies-in-spore |archiveurl=https://web.archive.org/web/20240221143759/https://www.straitstimes.com/singapore/wwii-video-points-to-secret-bio-warfare-studies-in-spore |archivedate=2024-02-21 |accessdate=2024-02-21 |newspaper=The Straits Times |language=en |issn=0585-3923}}</ref> From April to June 1943, the unit was temporarily stationed in Thailand to provide services for the construction of the [[Burma Railway|Thai-Burma railway]] before returning to Singapore.<ref name=":8" />{{Rp|27–28}}

In November 1944, the senior leadership of the Japanese Imperial General Headquarters realised their inability to halt the American offensive and decided to employ bacteriological warfare to demoralise the enemy. They ordered all bacteriological units to increase production. Unit 9420 was tasked with producing 60 kilograms of fleas, equivalent to the combined production of three bacteriological warfare units in North China, Central China, and South China, and second only to [[Unit 731]]'s production of 150 kilograms.<ref name=":8" />{{Rp|58–59}}

As the Japanese army suffered successive defeats on the Pacific front and considering the issue of post-war accountability, the Director of the Army Medical Bureau, [[Hiroshi Kambayashi]], announced the comprehensive termination of the biological weapons program.<ref name=":8" />{{Rp|68}} On 15 June 1945, Unit 9420 closed its experimental and production facilities in Johor. Initially, they withdrew to Singapore and later retreated to Laos. Before surrendering, they extensively destroyed relevant records.<ref name=":3">{{Cite journal |last=Cheong |first=Suk-Wai |date=2018-04-30 |title=Secret War Experiments in Singapore |url=https://biblioasia.nlb.gov.sg/files/pdf/vol-14/v14-issue1_SecretWar.pdf |journal=BiblioAsia |language=en |volume=14 |issue=1 |pages=18–23 |archive-url=https://web.archive.org/web/20230228144442/https://biblioasia.nlb.gov.sg/files/pdf/vol-14/v14-issue1_SecretWar.pdf |archive-date=2023-02-28 |access-date=2024-02-21 }}</ref><ref name=":1" /> After Japan's surrender, the unit moved to [[Saipan]] in November 1945 and then returned to mainland Japan in May 1946, landing at [[Nagoya]] before disbanding on the following day.<ref name=":8" />{{Rp|27–28}} This history of the unit remained unknown for decades until the truth began to be discussed by participants in the 1970s and 1980s.<ref name=":1" />

== Facilities ==
{{OSM Location map|coord={{coord|1.28047|127.83387}}|float=right|zoom=3|width=400|height=200|mark-coord1={{coord|1.28047|103.83387}}|mark-title1=King Edward VII College of Medicine, Singapore|shape1=n-circle|shape-color1=dark blue|shape-outline1=white|mark-size1=16|mark-coord2={{coord|1.52184|103.70581}}|mark-title2=Tampoi Mental Hospital, Johor Bahru, Malaysia|mark-coord3={{coord|2.7293226283398733|102.24983872662844}}|mark-title3=Tuanku Muhammad School, Kuala Pilah, Malaysia|mark-coord4={{coord|2.19200997466234|102.25452616918254}}|mark-title4=Malacca High School, Malacca, Malaysia|mark-coord5={{coord|4|51|38|N|100|44|52|E}}|mark-title5=Taiping Prison, Perak, Malaysia|mark-coord6={{coord|-6.899523271097696|107.60044963776609}}|mark-title6=Pasteur Institute of Indonesia, Bandung, Indonesia|caption=Known locations of Unit 9460 activities|auto-caption=12|mark-coord7={{coord|-6.213966833265471|106.89880444835266}}|mark-title7=Klender rōmusha camp, Jakarta, Indonesia|mark-coord8={{coord|-4.283414993426843|152.15400218626678}}|mark-title8=Tunnel Hill POW Camp, Rabaul, Papua New Guinea|mark-coord9={{coord|-6.823308346394716|155.74549245435315}}|mark-title9=Buin Underground Hospital, Buin, Papua New Guinea}}
Apart from its headquarters in Singapore, Unit 9420 had six branches in Malaya, Indonesia, the Philippines, Papua New Guinea, Thailand, and Myanmar.<ref name=":0">{{Cite web |author=Lim |first=Shao Bin |date=2017-08-13 |title=飞来的老鼠 |url=https://www.zaobao.com.sg/zlifestyle/culture/story20170813-786726 |archive-url=https://web.archive.org/web/20180427081227/http://www.zaobao.com.sg/zlifestyle/culture/story20170813-786726 |archive-date=2018-04-27 |access-date=2024-02-20 |website=Lianhe Zaobao |language=zh-hans}}</ref><ref name=":7">{{Cite web |author=Lim |first=Shao Bin |date=2018-02-28 |title=日本731部队和新加坡 |url=https://sfcca.sg/2018/02/28/%e6%97%a5%e6%9c%ac731%e9%83%a8%e9%98%9f%e5%92%8c%e6%96%b0%e5%8a%a0%e5%9d%a1/ |archive-url=https://web.archive.org/web/20240221194838/https://sfcca.sg/2018/02/28/%E6%97%A5%E6%9C%AC731%E9%83%A8%E9%98%9F%E5%92%8C%E6%96%B0%E5%8A%A0%E5%9D%A1/ |archive-date=2024-02-21 |access-date=2024-02-21 |website=[[Singapore Federation of Chinese Clan Associations]] |language=zh-hans}}</ref>

=== Singapore headquarters ===
[[File:Tan_Teck_Guan_Building,_Aug_07.JPG|link=https://zh.wikipedia.org/wiki/File:Tan_Teck_Guan_Building,_Aug_07.JPG|thumb|[[Tan Teck Guan Building]] used to be a [[Plague (disease)|plague]] lab]]
The headquarters of Unit 9420 was established at King Edward VII College of Medicine,<ref name=":2">{{Cite web |last=Ong |first=Tanya |title=SGH building housed secret Japanese lab for biological warfare during WW2 |url=https://mothership.sg/2017/11/sgh-building-housed-secret-japanese-lab-for-biological-warfare-during-wwii/ |archive-url=https://web.archive.org/web/20230228144316/https://mothership.sg/2017/11/sgh-building-housed-secret-japanese-lab-for-biological-warfare-during-wwii/ |archive-date=2023-02-28 |access-date=2024-02-21 |website=Mothership |language=en }}</ref> with six laboratories inside.<ref name=":3" /> The [[Tan Teck Guan Building]] served as a laboratory for glanders. The laboratories in [[Outram, Singapore|Outram]] were used to cultivate fleas from rats.<ref>{{Cite journal |last1=Chang |first1=Maria Hsia |last2=Hasegawa |first2=Takuma |date=2007 |title=War and Its Remembrance: The Perspective from Japan |url=https://www.jstor.org/stable/48602799 |journal=Democracy and Security |language=en |volume=3 |issue=1 |pages=45–88 |doi=10.1080/17419160601017727 |jstor=48602799 |s2cid=143233744 |issn=1741-9166 |archive-url=https://web.archive.org/web/20220324021331/https://www.jstor.org/stable/48602799 |archive-date=2022-03-24 |access-date=2024-02-21 |url-access=subscription }}</ref>

According to the research findings of Unit 731, the optimal climatic conditions for breeding fleas were a temperature of 22 degree Celsius and 76% humidity, which was consistent with the climate in Southeast Asia.<ref name=":0" /> In 1943, the Japanese military transported over 30,000 rats from Tokyo to Malaya.<ref name=":1" /> In October 1944, another 30,000 rats were transported from Tokyo to Singapore. Additionally, the Japanese military used animal specimens from the [[National Museum of Singapore|Raffles Museum]] for research, considering hamsters, squirrels, and guinea pigs as supplements to rats.<ref>{{Cite news |last=Fang |first=Chin Soo |date=2022-02-14 |title=Cultivating smallpox, plague: S'pore was a major biological warfare centre during WWII |url=https://www.straitstimes.com/singapore/cultivating-smallpox-plague-spore-was-a-major-biological-warfare-centre-during-wwii |archive-url=https://web.archive.org/web/20221005084850/https://www.straitstimes.com/singapore/cultivating-smallpox-plague-spore-was-a-major-biological-warfare-centre-during-wwii |archive-date=2022-10-05 |accessdate=2024-02-20 |newspaper=The Straits Times |language=en |issn=0585-3923 }}</ref>

For every ten thousand rats, ten kilograms of fleas could be produced. Malaya Peninsula thus became the largest flea farm for the Japanese military outside of Japan and China. Researchers fed captured rats, injected them with Yersinia pestis, causing the rats to become sick and produce fleas. The fleas then fed on the dead hosts, and researchers separated them from the host's body, fed them blood, and every three to four months, they sent the fleas in glass bottles to Thailand.<ref name=":1" />

In addition to the plague, laboratories in [[Outram, Singapore|Outram]], Singapore also researched cholera, malaria, smallpox, typhoid fever, dysentery, and anthrax.<ref name=":3" /> Singapore historian Lim Shao Bin estimated that Unit 9420 may have also conducted human experiments and is currently under investigation.<ref name=":1" />

=== Malaysia branch ===
In Malaysia, Unit 9420 occupied [[Tampoi Mental Hospital]] in the northwest suburbs of [[Johor Bahru]] near Singapore to breed rats and develop biological weapons. The laboratory courtyard had facilities for breeding rats.<ref name=":0" /><ref name=":6">{{Cite journal |last=Majid |first=Marina Abdul |date=2018-01-15 |title=A Japanese biological weapon's legacy in Malaysia: the aftermath effects for environmental contamination, sustainable development and application of international humanitarian law |url=http://www.ijlgc.com/PDF/IJLGC-2017-06-12-06.pdf |journal=International Journal of Law, Government and Communication |language=en |volume=2 |issue=6 |pages=46–62 |archive-url=https://web.archive.org/web/20220520170627/http://www.ijlgc.com/PDF/IJLGC-2017-06-12-06.pdf |archive-date=2022-05-20 |access-date=2024-02-21 }}</ref> On the other side of the laboratory was an isolation wall with a 24-hour operating boiler outside to burn the bodies of rats and provide boiling water for disinfection.<ref name=":3" /> The soldiers stationed at Tampoi was divided into three divisions, namely Team Imura, Team Nakayasu, and Team Emoto. Team Imura infected fleas at the hospital. Team Nakayasu bred and experimented on [[flea]]s. Team Emoto captured and raised rats, which also had presence at  Selayang for some unknown reason.<ref name=":7" />

Besides Tampoi, Team Imura also controlled Tuanku Muhammad School, hiring local Chinese and Malay people to raise tens of thousands of rats and thousands of rabbits, where there was a Taiwanese-run rat farm nearby. [[Malacca High School]] was also once a site for flea breeding.<ref>{{Cite journal |last=Abdul Majid |first=Marina |date=2021-12-01 |title=Disease Bearing Insect Research In Malaya By Japanese Scientists During World War II And Its Position In International Law |url=http://www.ijlgc.com/PDF/IJLGC-2021-26-12-10.pdf |journal=International Journal of Law, Government and Communication |language=en |volume=6 |issue=26 |pages=69–89 |doi=10.35631/IJLGC.626007 |issn=0128-1763 |archive-url=https://web.archive.org/web/20220129111818/http://www.ijlgc.com/PDF/IJLGC-2021-26-12-10.pdf |archive-date=2022-01-29 |access-date=2024-02-21 }}</ref> According to British military tribunal records, the Japanese military tested a poison named "Ipoh" in the form of live human experiments at the [[Taiping Prison]] in [[Perak]].<ref>{{Cite journal |last=Abdul Majid |first=Marina |date=2018-07-01 |title=A Japanese War Crime: Human Experimentation with Poison in Taiping, Malaya During World War II |url=http://www.ijlgc.com/PDF/IJLGC-2018-09-06-03.pdf |journal=International Journal of Law, Government and Communication |volume=3 |issue=9 |pages=24–25}}</ref>

=== Indonesia branch ===
[[File:COLLECTIE_TROPENMUSEUM_s_Lands_Koepok_Inrichting_en_het_Instituut_Pasteur_exterieur_van_het_gebouw_Bandoeng._TMnr_60012974.jpg|link=https://zh.wikipedia.org/wiki/File:COLLECTIE_TROPENMUSEUM_s_Lands_Koepok_Inrichting_en_het_Instituut_Pasteur_exterieur_van_het_gebouw_Bandoeng._TMnr_60012974.jpg|thumb|Main Building of [[Bio Farma|Pasteur Institute of Indonesia]]]]
In Indonesia, Unit 9420 established branches in Jakarta and Bandung.<ref name=":3" />[[Iwane Matsui]] once visited the [[Bio Farma|Pasteur Institute of Indonesia]] in Bandung.<ref name=":3" /> In 1944, the failure of tetanus toxin vaccines developed by the Japanese army led to massive deaths at Klender rōmusha camp, Jakarta, which led to the arrest of the [[Eijkman Molecular Biology Research Center|Eijkman Institute]]'s scientific staff, including its director Professor [[Achmad Mochtar]], who was executed by the Japanese. All records of the Japanese research in the [[Bio Farma|Pasteur Institute]] was destroyed before the arrival of the [[Allies of World War II|Allied Forces]] in September 1945.<ref>{{Cite journal |first=J. Kevin | last=Baird |date=2016-01-01 |title=War Crimes in Japan-Occupied Indonesia: Unraveling the Persecution of Achmad Mochtar |url=https://apjjf.org/2016/01/4-Baird.html#sthash.PxN0hevq.dpuf |journal=The Asia-Pacific Journal |language=en |volume=14 |issue=1 |archive-url=https://web.archive.org/web/20200603071053/https://apjjf.org/2016/01/4-Baird.html/#sthash.PxN0hevq.dpuf |archive-date=2020-06-03 |accessdate=2022-04-25}}</ref>

=== Other branches ===
In northern Burma and western Yunnan, China, the Southern Army Unit 9420 Epidemic Prevention and Water Supply Department was stationed to collect and breed rats and cultivate bacteria.<ref name=":5">{{Cite web |date=2013-07-30 |title=731研究者发现日军滇西细菌战新罪证 |url=https://www.chinanews.com.cn/gn/2013/07-30/5103140.shtml |archive-url=https://web.archive.org/web/20240221134321/https://www.chinanews.com.cn/gn/2013/07-30/5103140.shtml |archive-date=2024-02-21 |access-date=2024-02-20 |website=China News Service |language=zh-hans}}</ref>

In Papua New Guinea, Unit 9420 established branches in [[Rabaul]] and [[Buin, Papua New Guinea|Buin]].<ref name=":7" /> At Rabaul, Japanese military doctor Einosuke Hirano was witnessed to have experimented on prisoners of war from the United States, Australia and New Zealand.<ref name=":7" /> American Lieutenant James McMurria, as a prisoner of war, witnessed human experiments at the Rabaul Tunnel Hill POW camp and testified to the U.S. War Department after the war.<ref>{{Cite web|date=1948-07-21 |title=Perpetuation of Testimony of Former 1st Lieut. James A. McMurria, O-373644 In the matter of the POW Camp operated by the 6th Field Kempai Tai Headquarters in Rabaul, New Britain - Tunnel Hill POW Camp |url=http://www.mansell.com/pow_resources/camplists/other/rabaul/mcmurria_affidavit_rabaul.html |website=McMurria affidavit; RG 331 Box 943 Rabaul Reports}}</ref> In the Philippines, Unit 9420 established a branch in Manila.<ref name=":7" /> The locations and the functions of Thai and Burmese branches of the unit remains unknown.<ref name=":7" />

== Relevant battles ==
[[File:Lta-balloons-japan-wwii-balloon-bombs-(Fu-Go).jpg|link=https://zh.wikipedia.org/wiki/File:Lta-balloons-japan-wwii-balloon-bombs-(Fu-Go).jpg|left|thumb|[[Fu-Go balloon bomb]]s]]
During the Invasion of Buka and Bougainville in 1942, the British troops were under attack from plasmodium which was cultured in Singapore.<ref name=":3" /><ref name=":1" /> Unit 9460 also participated in the massive biological weapons attacks in Yunnan, China.<ref>{{Cite web |last= |first= |title=旧日本軍の細菌部隊・岡9420部隊の名簿が一般公開―中国メディア |url=https://www.recordchina.co.jp/b833024-s10-c30-d0035.html |archive-url=https://web.archive.org/web/20210604130851/https://www.recordchina.co.jp/b833024-s10-c30-d0035.html |archive-date=2021-06-04 |access-date=2024-02-20 |website=Record China |language=ja }}</ref> Starting from 4 May 1942, Japanese forces bombed Baoshan, Yunan on the [[Burma Road]] with [[cholera]] weapons, after they had bombed the town with incendiary munitions since 3 January 1941.<ref name=":8" />{{Rp|95–96}}In the meantime, Japanese forces also recruited Taiwanese, disguised as students, to release cholera bacteria into ditches, wells, and ponds along Burma Road.<ref name=":5" /><ref name=":8" />{{Rp|90}} This led to a cholera outbreak near Baoshao, which lasted until mid-July.<ref name=":8" />{{Rp|106–108}} This outbreak spread to the whole western Yunan, with no exact number of deaths confirmed. The maximum casualties from the outbreak could be as many as 120 thousand.<ref name=":8" />{{Rp|119–123}}
[[File:Rats_in_Burma_-_UK_Int.png|link=https://zh.wikipedia.org/wiki/File:Rats_in_Burma_-_UK_Int.png|thumb|A British report showing that the Japanese were collecting rats and mice from the local Burmese in 1943-1944]]
Between 1943 and 1944, the Japanese military forcibly collected rats from the population in Burma and Yunnan under the pretext of epidemic investigation.<ref name=":8" />{{Rp|119–123}}Subsequently, they bred and released infected rats through epidemic prevention and water supply units in places like Mangshi and Tengchong, causing an outbreak of plague. The plague spread along Burma Road, affecting areas from Ruili to Dali and then spreading eastward to the Nujiang River. It was not fully controlled until 1953,<ref name=":8" />{{Rp|175–176}} with approximately five thousand deaths.<ref name=":8" />{{Rp|188}}

After the failure of the Guadalcanal Campaign in 1943, the Japanese military began planning to launch bacteriological warfare on the Pacific front but none were executed. On 14 December 1943, Lieutenant Colonel Kaneko Jun'ichi of the Army Medical School's Epidemic Research Laboratory submitted the "PX Effect Estimation Algorithm," estimating the effects of bacteriological warfare. It was estimated that one kilogram of fleas could cause the deaths of 11 people in the North Pacific and 11,200 people in the Southwest Pacific.<ref name=":8" />{{Rp|45,48}}

On 26 April 1944, at a meeting of the Army Ministry Directors, Chief of Staff of the Operations Department, [[Takushiro Hattori|Hattori Takushiro]], proposed using submarines to launch plague attacks on [[Sydney]], [[Melbourne]], [[Hawaii]], and [[Midway Atoll|Midway Island]] in an attempt to regain strategic advantage in the Central Pacific. However, part of the bacteriological warfare unit, which departed in April, was destroyed by the U.S. military on [[Saipan]], and another part died in a submarine attack by the U.S. military en route to the [[Chuuk Lagoon|Truk Islands]], resulting in the failure of the plan.<ref name=":8" />{{Rp|50–53}}Later the year, the Japanese military launched [[Fu-Go balloon bomb]]s, but they caused only six fatalities in the United States.<ref name=":8" />{{Rp|61}} In 1945, the Japanese military proposed the "Night Cherry Blossom" plan, but it was never implemented due to Japan's defeat.<ref name=":8" />{{Rp|67–68}}

== Historiography ==
[[File:JAPANESE_MEDICAL_REPRESENTATIVES_ARRIVING_AT_HEADQUARTERS_2_CORPS_SURRENDER_PARTY_CAMP_IN_THE_KAHILI_AREA_TO_DISCUSS_WITH_AUSTRALIAN_OFFICERS_ARRANGEMENTS_FOR_THE_COMPLETION_OF_THE_JAPANESE_SURRENDER.png|link=https://zh.wikipedia.org/wiki/File:JAPANESE_MEDICAL_REPRESENTATIVES_ARRIVING_AT_HEADQUARTERS_2_CORPS_SURRENDER_PARTY_CAMP_IN_THE_KAHILI_AREA_TO_DISCUSS_WITH_AUSTRALIAN_OFFICERS_ARRANGEMENTS_FOR_THE_COMPLETION_OF_THE_JAPANESE_SURRENDER.png|thumb|250x250px|Japanese medical doctors to talk with the Allied about Japanese surrender in Buin, Papua New Guinea, in September 1945]]
Members of Unit 9420, after handing over experimental data and information to the United States, did not face any punishment and gradually became doctors, scholars, or politicians, retiring one after another starting from the 1980s.<ref name=":1" /> Among them, Ryōichi Naitō founded a biological company named Green Cross, with Kurobuta Ichirō Ota, another member of Unit 9460, as the director of the company's Kyoto branch. Akio Kihoin founded the Kyoto Institute for Microbiology. Fujino Tsunesaburō became a professor at [[Osaka University]]. Kiyoshi Hayakawa founded Hayakawa Institute of Preventive Medicine.<ref name=":7" /> When younger doctors learned about their history, they were shocked, and some formed non-governmental organizations to publicly disclose their understanding of what happened back then. Lim Shao Bin pointed out that surviving members of Unit 731 lacked remorse for their behaviour, and Singaporeans lacked understanding of the history before [[History of Singapore|Singapore's independence]] in 1965.<ref name=":3" />

In 1991, [[Othman Wok]] revealed to [[The Straits Times]] his experience in the laboratory developing glanders vaccine and believed he was actually involved in the development of bacteriological weapons.<ref>{{Cite news |last=Phan |first=Ming Yen |date=1991-09-19 |title=WWII germ lab secret |url=https://eresources.nlb.gov.sg/newspapers/digitised/page/straitstimes19910919-1.1.24 |archiveurl=https://web.archive.org/web/20240221134033/https://eresources.nlb.gov.sg/newspapers/digitised/page/straitstimes19910919-1.1.24 |archivedate=2024-02-21 |work=The Straits Times |page=24 |language=en}}</ref><ref name=":3" /> In November 2017, Singaporean researcher and collector Lim Shao Bin gave a lecture on the topic at the National Library of Singapore, once again drawing attention.<ref name=":3" /> In 2019, Lim Shao Bin and others released a black-and-white film footage taken by members of Unit 731 sent to inspect Singapore from 1942 to 1943.<ref name=":4" /> In September 2020, the Museum of Evidence of War Crimes by Japanese Army Unit 731 held a special exhibition on the archives of bacteriological warfare by the Japanese invaders, publicly displaying the roster of members of Unit 9420 obtained from the Ibaraki Branch of the National Archives of Japan for the first time.<ref>{{Cite web |title=中国首次公开日军9420细菌部队成员名册 |url=https://www.zaobao.com.sg/realtime/china/story20200903-1082090 |archive-url=https://web.archive.org/web/20220822181640/https://www.zaobao.com.sg/realtime/china/story20200903-1082090 |archive-date=2022-08-22 |access-date=2024-02-20 |website=[[Lianhe Zaobao]] |language=zh-Hans}}</ref>

== See also ==
* [[American cover-up of Japanese war crimes]]
* [[Sook Ching]]
* [[Unit 731]]

== References ==
{{Reflist}}

==Further reading==

* {{Cite book |last=竹花香逸 |url=https://books.google.com/books?id=P5oPyAEACAAJ |title=ノミと鼠とペスト菌を見てきた話: ある若者の従軍記 |date=1991 |publisher= |language=ja |chapter=}}
* {{Cite conference |last=Lim |first=Shao Bin |date=2019-11-23 |title=南方軍防疫給水部の記録を探じ求めて |url=http://731butaiten.jp/nannpugunnbouekikyuusuibu_20191125_0001.pdf |conference=15年戦争と日本の医学医療研究会第46国定例研究会 |language=ja |archive-url=https://web.archive.org/web/20230506064632/http://731butaiten.jp/nannpugunnbouekikyuusuibu_20191125_0001.pdf |archive-date=2023-05-06}}
* {{Cite book |last=张华 |title=侵华日军第9420部队及云南细菌战研究 |publisher=中国社会科学出版社 |year=2018 |isbn=978-7-5203-2419-9 |location=北京}}
{{IJA special research units}}
{{Authority control}}

[[Category:Japanese biological weapons program]]
[[Category:Japanese prisoner of war and internment camps]]
[[Category:Imperial Japanese Army]]
[[Category:Japanese human subject research]]
[[Category:Singapore in World War II]]
[[Category:Japanese war crimes]]