Unit Oka 9420 was the central Epidemic Prevention and Water Purification Department of the

Southern Expeditionary Army Group The was a general army of the Imperial Japanese Army during World War II. It was responsible for all military operations in South East Asian and South West Pacific campaigns of World War II. Its military symbol was NA. The Southern Expedition ...

of the

Imperial Japanese Army The was the official ground-based armed force of the Empire of Japan from 1868 to 1945. It was controlled by the Imperial Japanese Army General Staff Office and the Ministry of the Army, both of which were nominally subordinate to the Emperor ...

. Formed in 1942 to support the Japanese Southern Army, Unit 9420 consisted of two units; the Umeoka Unit, which specialized in the

plague Plague or The Plague may refer to: Agriculture, fauna, and medicine *Plague (disease), a disease caused by ''Yersinia pestis'' * An epidemic of infectious disease (medical or agricultural) * A pandemic caused by such a disease * A swarm of pes ...

, and the Kono Unit, which specialized in

malaria Malaria is a mosquito-borne infectious disease that affects humans and other animals. Malaria causes symptoms that typically include fever, tiredness, vomiting, and headaches. In severe cases, it can cause jaundice, seizures, coma, or deat ...

. Most of its work involved preventing the spread of disease in Singapore. Commanded by Major General Kitagawa Masataka, the unit was headquartered in the Permai Hospital in Tampoi,

Johor Johor (; ), also spelled as Johore, is a state of Malaysia in the south of the Malay Peninsula. Johor has land borders with the Malaysian states of Pahang to the north and Malacca and Negeri Sembilan to the northwest. Johor shares maritime b ...

, near the southern tip of the

Malay Peninsula The Malay Peninsula ( Malay: ''Semenanjung Tanah Melayu'') is a peninsula in Mainland Southeast Asia. The landmass runs approximately north–south, and at its terminus, it is the southernmost point of the Asian continental mainland. The are ...

, 13 km northeast of Johor Bahru and

Singapore Singapore (), officially the Republic of Singapore, is a sovereign island country and city-state in maritime Southeast Asia. It lies about one degree of latitude () north of the equator, off the southern tip of the Malay Peninsula, borde ...

, with some evidence that it also had sub-units operating in Thailand and working on unknown diseases. Coupled with its work on the plague, the unit was also responsible for rat catching. According to the testimony of politician Othman Wok, Singapore was also an important

biological weapon A biological agent (also called bio-agent, biological threat agent, biological warfare agent, biological weapon, or bioweapon) is a bacterium, virus, protozoan, parasite, fungus, or toxin that can be used purposefully as a weapon in bioterroris ...

s (BW) base. A laboratory was established there within days of the Japanese conquest. It became one of the largest of the BW installations outside of mainland China. Initially, Unit 9420 was under the command of Hareyama Yoshio, but in 1942, Lieutenant Colonel Naito Ryoichi, one of Ishii's most trusted colleagues, assumed control of the facility for several years. It was staffed with approximately 150 physicians and scientists, and produced huge quantities of

pathogen In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a ger ...

s annually. Naito and his staff worked primarily with

typhus Typhus, also known as typhus fever, is a group of infectious diseases that include epidemic typhus, scrub typhus, and murine typhus. Common symptoms include fever, headache, and a rash. Typically these begin one to two weeks after exposure. ...

, plague, and pesticides. It is unknown whether Singapore was a BW research facility, or whether it was simply a laboratory employed to produce pathogens for use elsewhere.Sidu H. ''The Bamboo Fortress: True Singapore War Stories''. Singapore: Native Publications; 1991; also printed in

Straits Times ''The Straits Times'' is an English-language daily broadsheet newspaper based in Singapore and currently owned by SPH Media Trust (previously Singapore Press Holdings). ''The Sunday Times'' is its Sunday edition. The newspaper was establish ...

, 19 September 1991

References

Japanese biological weapons program Imperial Japanese Army Japanese human subject research History of Singapore Japanese war crimes {{Japan-mil-hist-stub