Diabolical Science: Uncovering Unit 731 and Other Japanese Biological and Chemical War Crimes

Kas 158 (Modern Japan) Final Paper

The Zoomer Historian
19 min readJul 2


What are you willing to do in devotion to science? How far you will go in the name of your nationalist pride and scientific pursuit? Is knowledge still worth pursuing if it is at the expense of the lives of actual human beings? History, specifically in the 20th century, will tell us that there were scientists who were willing to set aside their moral faculties in exchange of their desire to find answers, mostly because those answers might become useful to the state that they display their pride with. Just looking at Europe during the first half of the previous century will already give us plenty of examples.

There was the German chemist Fritz Haber who aside from inventing ammonia that revolutionized fertilizers in agriculture and fed millions of lives, also invented chemical weapons that killed millions of soldiers from the enemy lines during the First World War. There were also J. Robert Oppenheimer and other scientists who led the Manhattan Project, which developed nuclear weapons for the United States government that they eventually dropped into the cities of Hiroshima and Nagasaki, instantly perishing hundreds of thousands of innocent civilians. And do I even have mention Josef Mengele? The mad Nazi scientist behind the horrific experiments towards Jewish prisoners in Auschwitz concentration camp. The list of war crimes that Nazi Germany committed for scientific research could fill volumes of books.

Japanese Kwantung Army who worked inside Unit 731

However, it can be argued that nothing will ever beat the severity and brutality of human experiments committed by Imperial Japan, to the point that calling them scarier than any sci-fi horror movies would be an understatement. Unfortunately, none of the perpetrators were held accountable, none of the victims were given proper justice, and the stories of people who witnessed these atrocities are being downplayed by the current Japanese government and overshadowed by the stories of the Holocaust. This does not mean in any way to diminish the suffering of the Jewish people in the hands of the Nazis nor to deny that it happened at all, but only to give more spotlight to an underrated story of innocent civilians in China being murdered by the Japanese in the name of their diabolical science.

During the 19th century, Japan was getting behind from technologically progressing as a nation, as a direct result of the Tokugawa Shogunate’s closed-door policy against Western influences going into the islands. But since the arrival of US Navy under the command of Commodore Matthew Perry in 1853, Japan was forced to open themselves for world trade. Decades later, the shogunate was dissolved and the supreme authority of the emperor made a comeback, in the personality of Emperor Mutsohito, ushering in the Meiji Restoration period. This time, Japan is now determined to be progressively excellent. They reasoned that in order to avoid being under the sphere of influence by Western powers, just like what happened to China, they would have to match their greatness and dominance. Their first step began with technology and the military, and combined with their conservative Bushido code of loyalty, honor, and discipline, Japan became Asia’s rising superpower.

It was the 1930s and the military might of the Japanese Imperial Forces were getting stronger than ever over time. Their victories during the First Sino-Japanese War and the Russo-Japanese War proved to the West that they were a growing force to be reckon with. Now their divine emperor, Hirohito, wanted to take things much further. He wanted to show to the world the superiority of Japan as the leader of Asia free from Western hegemony — to “liberate” their neighboring countries from their imperialist aggressors and establishing Asia for Asians under their fascistic ideology of 大東亜共栄圏 Dai Toa Kyoeiken or “Greater East Asia Co-Prosperity Sphere”. But who are we kidding here, really? Of course, Japan’s ulterior motive is, first and foremost, show to all Asians who is the boss. Overdriven by their ambitions, the Japanese officials on the top (from the generals to the emperor himself) got greedier. They wanted more power.

One of the aftermaths of the Rape of Nanking

Japan started invading Manchuria in 1931, but it was not until the Marco Polo Bridge Incident on July 7, 1937 when their conflict with Chiang Kai-Shek’s Republic of China turned into the Second Sino-Japanese War. Japanese kempeitai forces seized the major cities of Beijing, Shanghai, and the capital, Nanjing. What happened in the latter city was just pure monstrosity, something that would be way worse than anyone’s nightmares. Piles of men and women lying on the streets while their severed heads chopped by katana thrown off in the corner, as well as babies impaled by bayonets. Around 20,000 women were sexually violated in every way possible, and properties were looted and burned down. This incident infamously called the “Rape of Nanking” was not just an isolated case of Japanese military displaying this kind of brutality, as they also later expanded their empire across Southeast Asia and the Pacific.

But it was not only the members of the military who became monsters in the name of their emperor, but also their scientists and doctors. The words “unethical” and “inhumane” is not enough to describe their methods of human experiments against innocent civilians and prisoners of war, because butchering farms animals inside a slaughterhouse would be considered far more humane that what these doctors did inside their laboratories and operating rooms. These are some of the numerous biological and chemical war crimes that the Japanese Empire had committed from the beginning od the Second Sino-Japanese War until the end of the Second World War, beginning with the most famous case of Unit 731.

Programs developing Japanese biological and chemical weapons were kickstarted in the 1930s, and purposefully violated the ruling of the 1925 Geneva Convention that specifically prohibits that use of these particular weapons. Part of the reason why these programs started is because Japan thought that the fact that countries under the League of Nations being banned to utilize biological and chemical weapons only further proves that they were effective at conducting warfare. After all, the most superior army in Asia (as they would like to think for themselves) deserves to have the most excellent methods of displaying their military prowess, right?

They started constructing their laboratories in Manchuria after the invasion of Japanese forces there and the establishment of the puppet state of Manchukuo. But why Manchuria, exactly? First, this was their chance to conduct their horrific experiments outside of their island nation. Just imagine what would the Japanese public think if they learned about what kind of atrocities these scientists were doing inside their homeland. Second, those Chinese civilians and prisoners that they thought were ethnically inferior to them were the perfect guinea pigs for their experiments. Of course, they cannot conduct them with Japanese citizens, that would be crazy. Those Chinese were low-cost (if anything, they did not cost a single nickel to them at all), and they can get them everywhere in Manchuria. But they were not the only nationality that became the victims of these Japanese scientists; there were also Soviet, Korean, Mongolian, British, and French prisoners of war and several foreigners who lived within the Manchurian borders.

Unit 731 and Shiro Ishii

The nightmare began with the establishment of Army Epidemic Prevention Research Laboratory or AEPRL, under the command of the chief doctor of the Japanese Imperial Army, Dr. Shiro Ishii 石井 四郎. Born into a high middle-class family descended from a daimyo, Ishii was given a high-quality education during his childhood, and developed a very keen interest in biology, particularly bacteriology and how bacteria cause infections inside the human body. In his medical study trip overseas, he learned about the biological and chemical research developed by Westerners, including the poison gasses innovated by Fritz Haber. He wanted to apply this knowledge to Japan and proposed the establishment of their own research programs. Indeed, it began in Manchuria by founding a secret research group known as the Togo Unit.

Their first research facility was built in a concentration camp in the province of Harbin which they called the Zhongma Fortress. At plain sight, it looked like a usual prison, as if nothing sinister was happening there. Most of the people being detained there were anti-Japanese political prisoners, bandits, common criminal, and basically anyone who were arbitrarily arrested by the kempeitai. At their arrival, these prisoners who given good and healthy foods such as meat, fish, wheat, rice, and sometimes even alcohol. But make no mistake, that was not in any way intended to treat these prisoners with hospitality, but to bring them into a healthy state as an initial part of their experiments. This is where it took a dark turn. Some of them were deprived of food and water, in order to measure the effects of starvation in the human body. Some of them were purposefully injected bacteria inside their bodies, and observed what happens next.

But the Zhongma Fortress was forced to shut down after incidents of a prison break in 1934 and an explosion inside one of the facilities a year later, primarily because they compromised the secretive nature of their research program. By 1936, the emperor himself, Hirohito, authorized that Ishii’s Togo Unit must be expanded and integrated into the army’s Epidemic Prevention Department. It was by then comprised of two units, the one being led by Ishii called the Ishii Unit, and the other called the Wakamatsu Unit under the command of Wakamatsu Yujiro. But by 1940, all of these research facilities were started being collectively called as the 関東軍防疫給水部本部 Kantogun Boeki Kyusuibu Honbu (Epidemic Prevention and Water Purification Department of the Kwantung Army), or also known for short as 731 部隊 Nana-san-ichi Butai (Unit 731). Other biological and chemical research units were also built around China like Unit 100, Unit 516, Unit 1644, Unit 8604, and Unit 9420 in Singapore, and all of them were connected to the networks of scientists and doctors under the control of Ishii.

Their test subjects were being nicknamed as 丸太 maruta or “logs” that came from an inside joke where they have to disguise their facilities to the local authorities and suspecting people as a lumber mill. In other instances, these researchers published their medical findings from these gruesome experiments into reputable peer-reviewed journals, and made it appear as if they conducted them with monkeys. What an excellent way to dehumanize the victims. The value of these prisoners’ lives was naught to them. They were nothing but a statistic from their perspective; mere guinea pigs that have the sole purpose of filling up their scientific data. Even some of the experiments were done not for the purpose of developing a major biological and chemical research innovation, but only because some of the scientists and doctors just feel like cutting people open up out of curiosity and playtime. Thus, deliberate starvation and injection of bacteria were just the tip of the iceberg of what was occurring inside the laboratories of Unit 731.

A depiction of Unit 731 workers conducting live vivisection on a female prisoner

One of their most notorious experiments were vivisections, in which the bodies of the victims were cut open while they were alive, just like what average biology students do with their living frog specimens inside their school laboratories. They usually do this after injecting bacteria like the plague, anthrax, dysentery, typhus, cholera, and others in order to determine their live effects inside the prisoners’ organs. Sometimes they also vivisect pregnant women for the sake of looking the insides of their fetus-filled uteri. There were also instances of amputating limbs and reattaching them in other parts of the body. Talk about a real-life human centipede. Removal of major organs was also a norm there, which includes removing the stomach and attaching the victim’s esophagus with their intestines. Bear in mind that they conducted all of these without the use of any anesthesia at all, for they believed that using it impacts the results of their experiments in a negative way.

One testimony from a former Unit 731 worker revealed his first experience of dissecting a prisoner purposefully infected by bubonic plague. He described the scream of his victim as being horrible and unimaginably agonizing as he slowly pierced his scalpel to their chest, until they finally stopped yelling from pain. Meanwhile, some doctors would expose the limbs of prisoners outside a harsh cold winter outside until they got rock solid from frostbite. The arms and legs were then either poured with hot water or left in a room temperature just to see if they will go back to their normal state. If they developed gangrene, the limbs of the victim were cut off until only the head and the torso remain. If they were still alive by then, they will be proceeded into plague injections and vivisections. At least the scientists made sure that the bodies of their specimen were used in their fullest capacity.

If those were not bad enough, some prisoners were also injected venereal diseases like gonorrhea and syphilis, forced the infected male and female victims to have sex, coerced the infected women to keep the baby, just to observe the possible effects of those STDs in the child. Of course, Unit 731 guards raping women prisoners was as casual as drinking a cup of coffee in an average morning, and if they get pregnant, the doctors will have another specimen to experiment on. Other things that they did include transfusing human blood from people with different blood types, outright transfusing animal blood, draining gallons of blood, exposing X-rays in lethal doses to observe the effects of excessive radiation, dehydrating bodies alive until they become mummified, repeatedly spinning bodies in circles in a centrifuge, exposing prisoners in various doses of deadly poisons, suffocating them inside gas chambers using their newly-crafted chemical weapons, locking them inside a pressure chamber until their eyes popped out of their sockets, and many other gruesome and cruel methods.

Unit 731 workers spraying mustard gas onto a child prisoner in one of their field tests

The brutality does not end inside the laboratories. Some of the experiments were done outside the fields, but still within the unit complex. Some Chinese prisoners were tied in a wooden pole unprotected, where their newly-crafted bombs were placed and varying proximity, in order to test the level of damage and the amount of shrapnel that the explosions will generate. This way, they could know how to best treat Japanese soldiers wounded by bomb explosions. Those who were lucky enough to remain alive went straight to the operating room for vivisection, while the unlucky ones went to the crematorium. Among other weapons tested to them were grenades, pathogen bombs, flamethrowers, bayonets, and knives. Other subjects were used to expose them in mustard gas, chlorine gas, phosgene gas, and others, to test how fast their manufactured gasses can kill a person on average. Eventually, those same gasses were utilized by the Japanese Kwantung Army against both Chinese Kuomintang and Maoist forces in the battlefields.

If you thought the atrocities of Shiro Ishii and his networks of doctors and scientists only occurred within the confines of Unit 731, prepare to be sorely mistaken. Together with Unit 100 and Unit 1644, they were also guilty of crafting pathogen bombs into the villages of Chinese civilians in order to artificially generate an epidemic. Between 1940 and 1941, Japanese aircrafts dropped flea-infested rats above the cities of Changde and Ningbo in Hunan Province, intended to spread bubonic plague among the populace. These plagues successfully spread across regions and killed thousands of people, as they perfectly planned. Japanese soldiers in hazmat suits also conducted expeditions in some Chinese towns with the objective of infesting wells, rivers, and water reservoirs with diseases like cholera, dysentery, anthrax, smallpox, and typhoid fever. Some soldiers would even casually go out giving candies and chocolates on unsuspecting hungry Chinese children. Little that they knew, those candies contain generous strains of anthrax and botulism. The bodies of dead children as a result were taken by scientists in order to be examined. At least around 400,000 Chinese civilians perished from this biological warfare conducted by Imperial Japan against them.

There was once even a plan on December 1944 to bring Japanese pathogen bombs on the American soil, as part of Japan’s plan to discourage the American military from attacking them further. It was dubbed as “Operation PX” or also known as “Operation Cherry Blossoms at Night,” masterminded by Vice-Admiral Jisaburo Ozawa, with the assistance of Ishii himself. Their plan was for disease-carrying Japanese aircrafts, manned by kamikaze pilots, to be launched by submarine aircraft carriers in the middle of Pacific Ocean, aimed directed at the US West Coast cities like San Francisco, San Diego, and Los Angeles. Those pathogen bombs were supposed to carry diseases like bubonic plague, typhus, cholera, anthrax, dengue, and others, for the purpose of spreading biological terror among the American population. Their planned attack was scheduled to occur on September 22, 1945, but by that time, Japan had already surrendered to the Allied Forces weeks earlier. By March 1945 however, the operation was cancelled due to it being opposed by General Yoshijiro Umezu.

A Unit 731 surgeon performing a vivisection

It is too difficult to say how many exactly perished due to the war crimes of Shiro Ishii and his associates. But it was sure as hell that absolutely none of the prisoners who entered the gates of the prison complex had made it out alive. To enter Unit 731 as a test subject was to guarantee terrible suffering and painful death beyond anyone’s imagination. It was estimated that around 580,000 people were slaughtered by the Japanese through their germ warfare and human experiments. Other estimates say that it was 200,000. Inside the Unit 731, around 3000 men, women, and children underwent experiments, mostly through vivisection, though one former worker there claimed that it was actually around 10,000. However, there were also instances where Japanese workers and crews inside the unit complex became subjects of experiments themselves due to them being accidentally infected by diseases like the plague that they assisted to infect the prisoners. There were also around thousands of troops in the battlefields that died as a result of the chemical weapons that they themselves used.

But it must be the case that the perpetrators behind these atrocities were tried for war crimes and crimes against humanity and issued the death penalty, right? Virtually none of them, in fact. What could have been death by hanging, only resulted to short prison sentence for these war criminals, mostly due to American intervention. During the time when Japan’s defeat against the Allies was beginning to look inevitable, Ishii ordered all of his scientists, doctors, and other personnel to destroy as much evidence as they can, in order to conceal everything that they have done there for years. However, they preserved most of their scientific data that they gathered from their human experiments. Now this is an extremely clever move done by Ishii which later became extremely useful for him and his associates to basically get away from committing mass genocide. By that time, any knowledge about Unit 731 was almost nonexistent, as they were commanded by Ishii to keep it a secret to the grave.

After the war, Ishii was arrested by US authorities in Japan, which was now under Allied control. They were meant to be interrogated by Soviet authorities regarding their involvement with Japanese biological and chemical warfare. The Americans coerced the Japanese to spill information about their supposed bioweapons, but they just would not reveal it. They only started sharing classified information once US told them that USSR will be involved on their war crime trials, because they do not desire to be tried under the Soviets. General Douglas MacArthur, the man in charge on Allied-occupied Japan, made a decision on what they should do. He demanded the scientific data that the scientists of Unit 731 gathered in exchange of full immunity from being tried in 1946 Tokyo War Crimes Tribunal. Those documents that Ishii preserved turned out to be their get out of jail free card.

MacArthur’s rationale here is that those scientific data can be extremely useful for American scientists in the future. Since testing on humans is banned in the US (and they were only allowed to use animals), they perceived that the information retrieved from experimenting humans was undeniably valuable, as there is no way that they can replicate those experiments there. Besides, this was their way of getting ahead with the Soviets, as they do not want communists to possess knowledge on Japan’s advance biochemical weaponry. Thus, the brewing ideological and political tensions between the Americans and the Soviets was part of the reason why almost none of the Unit 731 personnel was prosecuted in Tokyo. But the Soviets created a war crime tribunal of their own in Khabarovsk, where they conducted hearings in 1949 for 12 Japanese military and medical personnel involved with the use of biological weapons. However, the US dismissed the trials as a communist propaganda and a distraction to downplay what the Soviets did to their Japanese prisoners of war.

Shiro Ishii reunited with other former workers of Unit 731

In the end, they were only given, at best, minimal prison sentence, while Ishii and his Unit 731 people remained free, and lived their lives as if absolutely nothing happened at all. Some of the Unit 731 personnel even had professional job in medical fields, universities, and pharmaceutics, despite their secret involvement on a war crime. Ishii himself died of laryngeal cancer at the age of 67 in Tokyo, never taking accountability with everything that he did, and not showing any kind of remorse. But over time, some of them eventually came out and told their own story one way or another, on how they were responsible for massacring innocent civilians inside laboratories.

To be fair though, surely not all of the people who carried out those experiments were evil and sinister to their core. Most of them were probably just a terrified as their prisoners, since their superiors ordered them to carry out the horrific procedures lest they will be also killed. For example, a former Japanese army doctor named Akira Makino confessed with conducting vivisections and amputations against Moro people in Mindanao during the time when he was assigned in the Philippines from December 1944 to February 1945. He was told that he will be killed if he refused to do those procedures, and showed repeated remorse with what he did from right after the war until he got old.

By and large though, both the Japanese and American governments remained silent about the existence of Unit 731, mainly to honor each other’s deal that they created post-war. Not a single jot or tittle about their own human rights violations were being taught in most Japanese history classes, let alone what the Japanese scientists and doctors did in Manchuria. It was not until 1988 when Japan finally admitted about Unit 731 and their biological and chemical warfare research programs being real. The Japanese government only fully disclosed all of the names of personnel involved by 2018. However, despite their efforts to recognize what happened, Japan is yet to apologize about Unit 731 up until now. In fact, none of the terrible things that they did during the reign on Imperial Japan had undergone an official apology and reparations to their Chinese and Koreans victims. No wonder why a lot of their East Asian neighbors still hate their guts to this day.

As much as we desire to ignore this, most of the scientific data that the Japanese acquired through diabolical means turned out to be very useful to the scientific community today. Plenty of information about the limitations and the extremes that the human body can endure will not be possible for us to know if not because of Unit 731. Infectious disease experts and microbiologists of this day are actually getting some wisdom the Shiro Ishii’s horrible pathogenic experiments in order to better understand the spread of viruses in light of the current COVID-19 pandemic. This now begs the question, do we even deserve possessing these kind of knowledge today, knowing that they were produced through an immoral manner?

The truth is, science has no moral dimension. It does not care if one would utilize it in a good way or in a bad way. It does not give a damn if you are pursuing knowledge through ethical or unethical means. Use it for the betterment of humanity or its destruction, either way you will succeed. Because it simply works, period. But as community of people who still care about each other, there is still a need to draw a line on how far should we go on our desire to chase scientific truth, and how much science should be involved in politics. We have abused science before, and using our historical consciousness, it is an imperative that we should watch out on the next possible Shiro Ishii or Josef Mengele that might repeat the horrors of the past all over again.


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Passed on June 30, 2023



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