by Chew Yong Jack

As a subordinate unit of the infamous Japanese biological warfare Unit 731, the Oka (岡in kanji or Steel) 9420 unit based in Singapore had been not much more than a mere footnote in history. In fact, in Daniel Barenblatt’s “Plague Upon Humanity” (Harper Collins, 2004), which got me acquainted to this little known factoid, it was merely mentioned that:

The [731] network ultimately included secret bases along the Russian border …. Singapore, the Philippines and New Guinea (p. 36).

and

[Ryoichi] Naito was himself a top university professor who had been director of the Unit 731 branch unit in Singapore, a civilian cohort of [Shiro] Ishii, with special expertise in the analysis of human blood (p. 47)

With the rather limited primary materials I had come by so far, I can make no claims of being able to shed much more light on the subject. However, a picture (incomplete and hazy as it doubtlessly is) can be pieced together of the inner-workings and operations of Oka 9420.

Origins

Ostensibly, Oka 9420 acted as a medical unit attached to the 25^th Japanese Army occupation force in Singapore. Its first traceable contribution to the Japanese military administration in Singapore was in the inaugural Gunsei Geppou (軍政月報) issued in March 1942 which contained a section warning of the dangers of an outbreak of para-typhus in Singapore. It is quite likely that the public health warnings posted by the military administration in the Syonan Times under the – with hindsight of course – whimsically titled “M.A.D Notices” (M.A.D being the unfortunate acronym for “Military Administration Department”) also involved inputs from Oka 9420.

Oka 9420’s facilities were located in the Singapore General Hospital as well as the College of Medicine Building area along College Road. According to former Minister for Social Affairs Mr Othman Wok - who was a lab assistant tasked to remove fleas from rats, the bubonic plague laboratory was situated in the Tan Teck Guan building (Straits Times, 19/09/1991).

Command Structure

Oral accounts by those who worked for Oka 9420 offer at most a hazy conception of its structure. Mr Othman Wok, who had trapped rats for the unit’s laboratories, mentioned that he was under two colonels and four senior privates (ibid). Mr Chelliah Thurairajah Retnam, a local volunteer of the British Royal Army Medical Corp before working for Oka 9420’s “Analyst Department”, mentioned reporting to a “Major Nato” (National Archives, Accession No 579).

Assuming that Mr Retnam had not mistakenly referred to Oka 9420’s director Ryoichi Naito, a civilian researcher, as “Major Nato”, it was quite likely that military personnel had resided in the middle tiers of the command structure. Sandwiching this group would be director Naito at the top and local staff members like Mr Retnam and Mr Othman Wok at the base.

It is not clear how many locals were in Oka 9420’s employ. Mr Retnam recalled that in the “Analyst Department” that he had worked for, there were about fifty to sixty local staff members – including future luminaries such as Eddie Barker (former Minister of Law) and Phay Seng Whatt (former Chairman, Public Service Commission). There were also an unknown number of those who worked on a part-time basis for specific assignments like rat catching. Mr Othman Wok estimated that about forty were involved in trapping rats for the unit (Straits Times, 19/09/1991).

Known Activities

Mr Othman Wok’s experience in working with Oka 9420 was possibly the most revealing of the sinister nature of the unit’s work here in Singapore. Responsible for picking fleas from rats, he also witnessed how the fleas were fed blood of rats infected by plague, as he described below:

Each flea was then put in a test-tube, which was inverted over a rat’s stomach which had been shaved [sic] of its fur. The flea then fed on the rat, which had been injected with plague serum (ibid).

During my face-to-face interview with Mr Othman Wok on 7 March 2006, he revealed that the “research team” was careful to dispose of the carcasses of infected rats. He said that he had learned from a driver assigned to the unit that the fleas bred as vectors for plague were transported to Thailand. At the time, Mr Othman Wok was unaware of the purpose of his work and it was not until after the war when he read that the Japanese “had bombed Chongqing with bottles of fleas”* that he realised the implications of his work for Oka 9420 (ibid).

When I asked him what happened to Oka 9420’s facilities at Singapore General Hospital after the Japanese surrendered, Mr Othman Wok said he had heard that the unit destroyed all evidence of its existence even before the surrender.

In contrast to Mr Othman Wok’s experience, Mr Retnam’s work with the “Analyst Department” was apparently far removed from Oka 9420’s more sinister activities. His work with the unit only included malaria prevention while he was in Singapore and the supplying and ensuring the sanitation of water for his assignment in Kachanaburi, Thailand. Unit 9420 had the necessary water filtration equipment and expertise to supply water to the worksite at River Kwai.

From Mr Retnam’s description, Oka 9420’s work was thus nothing more than the prevention of water-borne diseases such as cholera and typhoid (National Archives, Accession No 579). The only experience common to both Mr Retnam and Mr Othman Wok was the physical abuse at the hands of rank-and-file Japanese soldiers who were typically high-handed and brusque in their treatment of locals.

However, it should be noted that the different experiences by both men actually illustrated the modus operandi of the Japanese biological warfare programme. After all, Ishii’s Unit 731 had as its official designation “Epidemic Prevention and Water Supply Unit of the Kwantung Army”. Ishii himself had also made his mark in the Japanese army through his invention of a portable water filtration device for usage in the field (Barenblatt, 2004).

A Question to Ponder

One big question left unanswered could be whether Oka 9420 had restricted its activities in Singapore to sample collection, research and breeding of fleas as vectors.

Could Oka 9420 have used the initial chaos during the Japanese invasion of Malaya and Singapore as an opportunity to conduct field testing as it had done in China (where attacks were known to have been conducted in Ningbo, Zhejiang and Jiangsu)? Could the public health warning for infectious diseases issued under the “M.A.D. Notices” in fact be caused by such sinister activities?

Given these unanswered questions, this short write-up is but no more than a tiny scratch on the surface of a topic which deserves further study by historians and history enthusiasts more resourceful than myself. While I harbour no expectations that my write-up could lead to further research by others, I do hope that it can play a small part in generating greater awareness and interest in Oka 9420.

Currently working in the government, the author graduated with honours from the Department of History, National University of Singapore in 2003. This contribution is a follow-up to the author’s Chasing a “Dead” Lead (citizen historian, May 2007)

Notes

* There were no known biological attacks on Chongqing. Mr Othman Wok could have been referring to the use of biological weapons by the Japanese on Chongshan village in Zhejiang province. The Japanese had attacked Zhejiang province to search for pilots the Dootlittle raids on 18 April 1942 and Unit 731 had taken the opportunity to conduct field testing.

Bibliography

Daniel Barenblatt, A Plague Upon Humanity: The Secret Genocide of Axis Japan’s Germ Warfare Operation. New York: Harper Collins, 2004.

Aiko Kurasawa, Wartime Monthly Reports / Military Administration Monthly Reports (= Senji Geppou • Gunsei Geppou), 5 vols. Tokyo: Ryukei Shosha, 2000.

Tags: Japanese biological weapons research, Oka 9420, Othman Wok

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