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WW2: Japan's Secret Biological Weapons Program

Article #31 • Written by Alan Bellows

In 1945, just after Japan surrendered to the United States to end the second world war, a Japanese I-400 class submarine-- the likes of which Americans had never seen-- surrendered to a Navy destroyer. The Americans were surprised at the submarine's enormous size, and subsequent inspections continued to astonish. It was about 60% larger than the largest US submarines, twice as fast as the fastest US subs, and had the fuel capacity to travel around the Earth one and a half times before refueling. Perhaps most impressively, it was also an aircraft carrier.

The submarine had space for three specialized Japanese airplanes, called Seiran, which translates literally to "storm out of a clear sky." Before the Japanese surrender, this particular submarine's original mission had been to secretly sail westward from Japan to the US east coast, where an attack would be unexpected, and use its three aircraft to drop rats and fleas infected with bubonic plague, cholera, typhus and other diseases upon New York, Washington D.C., and other cities along the eastern seaboard. When problems made that plan infeasible, the sub was retasked to bomb the Panama canal from the east, but the end of the war arrived before the crew could carry out its mission.

By the end of World War 2, Japan had done quite a bit of experimentation with germ warfare, mostly in the form of infected fleas. The program got its start in the 1930s when Japan occupied Manchuria, and later in their invasion of China. These biological weapons were developed at Japan's Unit 731, an installation disguised as a water purification plant. The Allied forces had long suspected that Japan was utilizing germ warfare against China, but was unable to conclusively prove their suspicions during the war.

When America was attacked by Japanese balloon bombs, US officials were concerned that these might include some of Japan's infected flea payloads, but no such biological balloon bombs were ever discovered.

Several epidemics of cholera, typhoid, anthrax and bubonic plague were reportedly caused in China by Japan's "Uji" bombs, which were designed specifically to burst hundreds of feet above the ground, and rain infected fleas upon the populace. By some estimations, these attacks triggered outbreaks which killed as many as 50,000 Chinese people over six years. According to Chinese reports, infected houses, hospitals and other buildings were burned and had to be left untouched for decades, and fears of further outbreak still haunt the cities today.

Article written by Alan Bellows, published on 23 October 2005. Alan is the founder/designer/head writer/managing editor of Damn Interesting.

Article design and artwork by Alan Bellows.

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Posted 26 October 2005 at 11:26 am

Alan...please excuse me...I am a "newbie" at this, I meant in no way to plagerize you or your site!
I thought the article was from Wikipedia and was copywrite free. But if I have made a bad move I am sorry for the oversite, I find your site great and do not want to offend by my ignorance.
I will give proper credit in the future and change the current post today!

Alan Bellows
Posted 26 October 2005 at 12:06 pm

Understood... as long as you link to the article in question, you can include excerpts on your blog. It's just bad juju to copy the entire article without linking or attribution. Clearly it was an innocent mistake, so no harm done. We work hard to produce this content, so we like to be credited when it is used.

Posted 06 June 2006 at 11:39 pm

Bubonic plague? That gives new definition to the term "gettin medievil"

Posted 06 June 2006 at 11:49 pm

I particularly find the Japanese submarine most interesting... amazing given the date.

Posted 07 June 2006 at 03:05 am

This puts our nuking Japan in perspective. In retrospect, nuking Japan was the lesser of two evils, though whether the second bomb was necessary will forever be debated. It's unfortunate that we were pushed to that, but Japan not only had its own nuke program (as mentioned in the discussions re: the nuclear bombing of Hiroshima and Nagasaki), it intended to use biological warfare indiscriminately.

Meanwhile, Japan's war shrines decry the bombs we used as the worst atrocity ever, and their populace largly remains ignorant of what horrors Japan unleashed on those they fought. Their memorials even dare to say that they were "liberating" Asia. No wonder Korea and China get pissed when the Japanese PM visits Yasukuni, where Japanese war criminals are worshiped as deities of warfare.

Germany acknowledged and atoned for it's sins; Japan never did. Neither has Turkey atoned for the genocide of the Armenians. Don't get me wrong; the US has a good deal to acknowledge and atone for, but at least we have a free press, where the truth gets out, and people openly critique our history.

Posted 07 June 2006 at 05:03 am

yeah, the japanese military killed civilians, so the japanese civilians had to die!!!!

another viewpoint
Posted 07 June 2006 at 05:24 am

...drop plague infected fleas?...boy, wouldn't that itch and rub you the wrong way!

Posted 07 June 2006 at 07:18 am

For those of you that are interested, the Smithsonian Institution has the only remaining Seiran in the world. We have it on display at the new Air and Space museum in Northern Virginia. According to the docents the Japanese sailors were able to assemble the plane in 30 minutes.

Will Grimes
Posted 07 June 2006 at 08:25 am

This gives a good justification of use of the nuclear bomb that i did not know about before, the use of the atomic bomb by the USA in the Second World War seems more acceptable considering Japans intentions to attack civilians in some of Americas major cities.

Posted 07 June 2006 at 12:06 pm

Details of the Japanese biological warfare program can be found under the codename "unit 731".

And remember that the allies do not come out of this smelling of roses. They learned of the program after the war and then pardoned and officially denied everything involved in exchange of the data gained from the experiments. The experiments almost all amount to systematically torturing a human to death without anaesthesia, often with a live dissection if the poor test subject doesn't die to find out why they survived. The test subjects were both soldiers and civilians including old people, children and pregnant women. The 50, 000 deaths discussed in the parent article were caused when the war was drawing to a close and orders were given to hide the evidence. The scientists deliberately released their biological and chemical warfare agents into the local water supply and surrounding environment to kill as many civilians as possible. These scientists are still alive today unpunished, some even on a pension. Compare this to our treatment of the Nazis after the war.

Posted 08 June 2006 at 06:51 am

Nanking, Gila River, Kristallnacht, Haditha, Dachau, Hiroshima. The list goes on, yes? Tell you what: as fascinated as I am by war history, machinery, politics, and tactics, I sure do hate it.

And thanks, Gary for the quick mention of the last-gasp deaths caused at the end of the war – makes me want to find more information on the hiding of the biological agents by dumping them into the water to make a last statement - reminds me of burning oil wells in the gulf back in 1991. History repeats doesn't it? Any other sources you can point me to? Lemme know…

Meanwhile, I'm with GMan - that sub is freaking amazing! I'd never heard this story before, although I went deep into the balloon bomb story years ago. What a bizarre and fantastic piece of machinery, especially in the 1940's!

There have been a few stories about wartime machinery lately that all strike the same chord with me, based upon the view that “war begets pretty remarkable creative thinking”. I don’t buy that. The ideas and creative thinking is always there, isn’t it? Next, Politicians who bicker incessantly about AIDS research or allocations of funds for mental health clinics giggle with enthusiasm when a new multi-billion dollar bit of war machinery hits the sales floor. I'm thinking elliptically about this, but the age-old argument of need vs. want comes up again and again - the Japanese I-400 would never have been built unless the political force who funded it needed to kill people with it. All that creativity, inventiveness, and intellectual horsepower, just for a big ugly tin can purpose-built for blowing the crap out of things.

Sigh. I did it again, and the story wasn’t about the sub! Fleas, man, fleas! The hallmark of a Damned Interesting story…sends my puny brain down three different rabbit holes.

Posted 08 June 2006 at 08:43 am

thorndike said: "According to the docents the Japanese sailors were able to assemble the plane in 30 minutes."

Thirty minutes? Yikes! Wonder where we'll be technologically in a few years.

Posted 08 June 2006 at 11:33 am

I'd like to learn more about that submarine, any wiki articles on it?

Garnett Stancil
Posted 08 June 2006 at 05:50 pm

For more information about the I-400 and the airplane it carried, read the book, just published, entitled: The I-400. It is great! The airplane was already assembled. It just had folding wings, and folding tail sections. If you like history, boats, and airplanes, you will love this book.

Posted 09 June 2006 at 10:36 am

fargan Japs

Posted 09 June 2006 at 10:58 pm

This really DamnInteresting, been reading this and all the links for the last 2 hours.

I wish I have 20 lifetimes.


Dr. Bob
Posted 10 June 2006 at 03:54 pm

Most people think the atomic bomb was the worst thing we did from the air to Japan. Not true! The worst was the fire bombing of Tokyo which caused many more deaths the the atomic bomb.

With regard to atrocities, they happen in all wars. The difference is that it was policy in Japan whereas we usually punish those guilty of atrocities when we discover them.

Posted 16 June 2006 at 02:17 pm

Here's the wikipedia link for the 1-400 class sub:

Posted 08 January 2007 at 12:20 am

Glad to see someone publish this well kept secret. EVTV1 recently headlined a left wing bleeding heart video and article condeming the bombing. The generation that faced this enemy is rapidly disappearing. I was fortunate enough to spend some time with one of these soldiers. He told of how he and other POWs were placed in wooden, black boxes that were set in the sun to cook. They were placed in trenches and bureid up to their chest, then the ditches were used as a latrine where soldiers deficated and urinated on them. They were stripped and tied up by the hands and placed on carts that were then pulled around for the towns people to beat them with bamboo poles. It does not take much of an immagination to conclude that the fire baloons floated into California, may have been more of these bubonic fleas and maybe we set the fires to destroy them. Keep up the good work of exposing these attrocities.

Posted 14 February 2007 at 04:35 am

We run Miller Systems WW2 Campaign

and pride ourselves on having done some research on ww2 these passed 20 years.

We shouldn't be so 'holier than thou' and hypocritical here.
We hardly enter this issue with clean hands ourselves.

While the Japanese led the world in biological warfare even before ww2 started, the British led the world in chemical warfare, nerve agent/gas.

Two important distinctions.
The British tried to do their testing on isolated islands populated only with sheep. Granted there were still military and civilian casualties to be covered up, but we didn't deliberately test on humans as far as I know.
While some in the Japanese project did not see testing on humans as 'crossing the line'.
Very few people in any nation knew of the existance let alone actual methods of either program.

While Hitler had no qualms about using such weapons to further his Final Solution, even he refused to use such 'weapons of mass destruction' on even the 'sub-human' Russian front even when it might have prolonged his life, let alone won the war for him. And yet we did.
Historians believe this was because of his own experience as a casualty of mustard gas attack in ww1.
Yet the point remains, some could argue he had even more reason to use such a weapon than we did, his own survival, and yet he refused even to the end.

While we haven't suffered a nerve gas attack yet, the Japanese have. The Tokyo Sarin attack. Those convicted credited our ww2 programs for their success, not even the Japanese programs.

The nerve gas we fear will be used against us by terrorists today was not fathered by ww2 Japanese efforts, but our own(and the Nazis)

After ww2, America agreed to share the atom bomb with Britain in return for stockpiles of this same nerve agent. Despite the fact it is against both our laws.

When we found out about these projects, we rushed in and whisked them away. For trials and punishment as war criminals? No. We REWARDED them by making the protected American citizens with better pay and security to continue doing the work for us some of you say justified our using the atom bombs on them for.

Those few Japanese generals who did find out about these projects and risked their careers and even lives fighting to have these projects cancelled, were tried and convicted of war crimes by us while we gave citizenship and jobs to the illegal project itself.
Lesson: If you create and develop such illegal projects, you will be hired by the enemy. If you resist such projects you will still be tried as a war criminal.

I have seen a Japanese TV program indicating that the American gov't not only refused official Japanese request to return these 'criminals' to Japan to face trial on existing Japanese laws on the matter, but refused to even admit that they were made American citizens to continue those said same projects.

Did you know that we planned to use bio-chemical warfare on the German invasion beaches had they invaded England in ww2?

I've read and watched historians agree that when Churchill first viewed the effects of the German V1s after D-Day, infuriated, he ordered the bombing of German cities with their deadliest nerve agents. Fortunately his staff and Cabinet had the power to over-rule him.

If we say we had the right to use such weapons to win the war for us earlier and thus save lives in the long run, then do we justify anyone else doing the same thing, even our enemies?
Would Hitler then have been justified in using his own stockpiles to win the war in Russia for the same reasons? The Japanese vs China?

If we can say that the Japanese civilians deserved the atom bombs, (radiation and cancer and future generations of crippling genetic damage) BECAUSE they did not do enough to make sure their own governments weren't supporting, in any way, development and use of such weapons of mass destruction, atomic or biological or chemical...then would that apply to us too?

We shouldn't be so 'holier than thou' and hypocritical.
It only makes the world resent and distrust us all the more.

Apologies for the length, while presently an international advisor, I used to be a teacher.
I hope my points make some sense.

PS...I know a fair bit about those Japanese submarines ;).

Posted 14 February 2007 at 04:52 am

Re: Japanese giant subs.

Clyde Cussler, author, historian and novelist I believe sponsored an expedition on a TV program 'The Sea Hunters' that found that one group of scuttled giant I-class submarines intended to attack and destroy the Panama Canal....from the Atlantic side no less.

It has been hard for us, used to seeing seemingly dumbfounded little Japanese men in loin-cloths wielding pre-ww1 arms surrendering at war's end, and yet the Japanese were in fact superior designers and engineers to us in some surprising ways. Not least of which were their submarines. Indeed recently released documents from the former Soviet Union confirm that the present-day giant Soviet submarine program was copied directly from those Japanese giant subs they captured or recovered before the British and Americans scuttled them. It is a good thing for us that they found it 'dishonourable' to use submarines in merchant blockade that would in fact starve them out of the war, but instead committed them foolheartedly(in my opinion) in other roles.

I believe you can search and buy the episode, I am sorry I can't be of more help than that.

In my research in Asia, I've learnt some astonishing related facts to these amazing projects too.

Posted 05 May 2009 at 07:50 am

brandan said: "yeah, the japanese military killed civilians, so the japanese civilians had to die!!!!"

Correct innocent American were brutily killied and the japanese showed no mercy

Posted 25 April 2011 at 02:58 pm

Most Japanese civilians did not deserve to die (although no doubt some of them were actively aiding in the war effort). But neither did American citizens, nor for that matter did American soldiers deserve to die. The first and foremost responsibility of the president of the US is to protect the American people. Sending US soldiers to die by the 10's or 100's of thousands to avoid Japanese civilian deaths would be completely irresponsible. If you accept that the US was right to go to war with Japan (and I dont know anyone who does not accept that), then one cannot possibly justify letting our soldiers die in battle - or risking massive deaths of American civilians(!) - when it could be avoided by use of the atomic bombs. (Hypothetically, if American lives were not at stake - although of course they were! - is it justifiable to let Chinese civilians continue to get brutally slaughtered by the millions, rather than ending the war suddenly? If you think it is, dont answer me on that point (I am American), but please explain to some Chinese parent why we should be more concerned with Japanese civilian deaths.)

Posted 08 March 2014 at 08:11 am

The Japanese military have a history of being fearless and utterly ruthless it would not be unexpected that the Japanese possess the most virulent strains of viruses capable of destroying all species of mammalian life forms including humans . If the Japanese were to be cornered by China or Russia there is absolutely no doubt that that these biological weapons would be released,within in days these these viruses would circulate around the globe .After five years all mammals are eradicated .Nature then begins the process of rebuilding life , in about 10 million years dinosaurs reappear and end any chance of a human reserection

Peter Wandmose
Posted 06 June 2014 at 05:39 am

Did any from Unit 731go to USA working sharing knowledge.
Thanks great site

Posted 06 June 2014 at 01:23 pm

for those of you saying we nuked japan, you are wrong, no nuclear weapons have ever been used against an opposing threat in history, however, we used two ATOMIC bombs which are way different than nuclear bombs ( researched this arguement for hours to make sure i wasnt anyone ) because an atomic bomb splits the atom itself, a nuclear bomb splits the nucleas of said atom so no one ever got nuked

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