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.

Despite the brevity of Singapore’s existence, its history is an under-explored and one which occasionally does throw up a few surprises and interesting facts even for people who count themselves to be rather well-read. As an avid reader of history books, I had the good fortune to have experienced just such a surprise.

The surprise? Singapore’s role in Japan’s infamous biological weapons programme before and during the Second World War. The fact that Japan had a biological weapons programme during the war has been widely-known, primarily through various Chinese-produced documentaries, and the Unit 731 Museum located near Harbin, the provincial capital of Heilongjiang - which brings to life the various grisly details of vivisections, frost bite experiments, exposure to pathogens on life human subjects. However, Japanese military scientists’ activities in Singapore have been largely unheard of.

My first knowledge of Singapore’s connection to the Japanese military’s horrifying enterprise was through reading A Plague Upon Humanity by Daniel Barenblatt (Harper Collins, 2004). Delving into the history of Japan’s biological weapons programme, the book contains passing mentions of Singapore (in pp. 37, 47 and 206) which could be summed up by the following:

Unit 731 ran a network of secret facilities throughout its wartime empire including one in Singapore. Leading researcher Naito Ryoichi was at one time in charge of the unit’s activities in Singapore.

From then on, I was hooked. I wanted to find as much details about the subject as I possibly can. My search began with the Internet where I discovered that Unit 731’s branch in Singapore was designated as Oka (the Japanese word for steel) 9420. Thereafter, I came upon another juicy snippet in the unlikeliest of places – the National University of Singapore Library’s website (www.lib.nus.edu.sg).

In one of the pages covering the history of the library (see “Saved by a seal”) was a short write-up on the seal of the Oka 9420 unit found stamped on some of the books in the library. It reads:

Legend (as passed down verbally) has it that a Japanese officer had all the books in the Medical Library stamped with his troop’s seal [see below]. As a result, no other Japanese dared to destroy or damage them. This act on the officer’s part kept the Medical Library collection intact through World War II.

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By far the most interesting detail I uncovered from my Internet search was that Singapore’s former Minister of Social Affairs, Mr Othman bin Wok, had unwittingly worked for Oka 9420 on a part-time basis to supplement his family’s income. The far-out idea of attempting to get an interview with Mr Othman then sprang in my mind. My thought process went roughly from “He’s an important person” to “Who the heck am I to disturb him?” and finally to “What the heck! I’ll just do it to see what happens!”

Once again scouring the net, I had found Mr Othman’s office address and proceeded with writing a letter to the former minister to say that I was thinking of doing a master’s dissertation on this particular topic and would like to seek his help (which was genuinely a thought I hopefully nurtured – particularly if substantial information could be obtained from this interview). So, I mailed the letter on 15 February 2006.

To my utmost surprise, I received a letter about a week after from Mr Othman himself saying that I could liaise with his secretary to meet him for an interview. Admittedly, the only thing in my mind then was, “Wow! I’m meeting a former-minister? What are the odds?” After reality sunk in, I immediately set myself towards the task of compiling a list of questions in which I wanted to ask him. Subsequent to that, I excitedly counted down to the day of my appointment sometime in March 2006 to meet the man in the flesh.

When I finally met Mr Othman, it was a mixture of great joy and disappointment. Before the start of my interview, Mr Othman provided me with his own collection of press clippings on Japan’s biological weapons programme. They contained almost everything I wanted to know and I was very surprised that Mr Othman had gone through the trouble of reproducing them for my benefit. Among these clippings was a Straits Times exposé based on an interview with Mr Othman regarding his work with Oka 9420 (the story appeared on 19 September 1991).

My job of interviewing him was thus made that much easier – so easy in fact that my questions were restricted to finding out details which were not covered by the Straits Times exposé. Therein laid the mixture of my emotions — While I was certainly glad to have found out more details about Oka 9420, I could not help but feel a bit disappointed that the Straits Times had beaten me to it by fifteen years!

Notwithstanding my disappointment, my experience from this was mostly a positive one. For one, I learned that it does not hurt to try to seek out interviews with individuals no matter how important and highly-placed they might be. The crucial thing perhaps is that we should always try to convince our prospective interviewees of the seriousness and sincerity of our requests. I hope that by sharing my experience here, other hobbyist and serious historians might be similarly encouraged to pursue their interests without regard for preconceived notions of what is do-able and what is not.

Currently working in the government, the author graduated with honours from the Department of History, National University of Singapore in 2003.