Unit 731 was a covert biological and chemical warfare research and development unit of the Imperial Japanese Army that undertook lethal human experimentation during the Second Sino-Japanese War (1937–1945) and World War II. It was responsible for some of the most notorious war crimes carried out by Japanese personnel.
Unit 731 was based at the Pingfang district of Harbin, the largest city in the Japanese puppet state of Manchukuo (now Northeast China).
It was officially known as the Epidemic Prevention and Water Purification Department of the Kwantung Army. Originally set up under the Kempeitai military police of the Empire of Japan, Unit 731 was taken over and commanded until the end of the war by General Shiro Ishii, an officer in the Kwantung Army.
Between 3,000 and 12,000 men, women, and Children from which around 600 every year were provided by the Kempeitai died during the human experimentation conducted by Unit 731 at the camp based in Pingfang alone, which does not include victims from other medical experimentation sites. Almost 70% of the victims who died in the Pingfang camp were Chinese, including both civilian and military. Close to 30% of the victims were Russian. Some others were South East Asians and Pacific Islanders, at the time colonies of the Empire of Japan, and a small number of the prisoners of war from the Allies of World War II (although many more Allied POWs were victims of Unit 731 at other sites).
Many of the scientists involved in Unit 731 went on to prominent careers in post-war politics, academia, business, and medicine. Some were arrested by Soviet forces and tried at the Khabarovsk War Crime Trials, others surrendered to the American Forces. It has been postulated that one reason the scientists were not tried was that the information and experience gained in the studies of the biological warfare was of a great value for the United States biological weapons development program. On 6 May 1947, Douglas MacArthur, as Supreme Commander of the Allied Forces, wrote to Washington that “additional data, possibly some statements from Ishii probably can be obtained by informing Japanese involved that information will be retained in intelligence channels and will not be employed as ‘War Crimes’ evidence.” The deal was concluded in 1948.
In 1932, General Shirō Ishii, chief medical officer of the Japanese Army and protégé of Army Minister Sadao Araki was placed in command of the Army Epidemic Prevention Research Laboratory. Ishii organized a secret research group, the “Tōgō Unit”, for the conduct of various chemical and biological investigations in Manchuria. Ishii had proposed the creation of a Japanese biological and chemical research unit in 1930, after a two-year study trip abroad, on the grounds that Western powers were developing their own programs. One of Ishii’s main supporters inside the army was Colonel Chikahiko Koizumi, who later became Japan’s Health Minister from 1941 to 1945. Koizumi had joined a secret poison gas research committee in 1915, during World War I, when he and other Japanese army officers were impressed by the successful German use of chlorine gas at the second battle of Ypres, where the Allies suffered 15,000 casualties as a result of the chemical attack.
Unit Tōgō was implemented in the Zhongma Fortress, a prison/experimentation camp in Beiyinhe, a village 100 km (62 mi) south of Harbin on the South Manchurian Railway. A jailbreak in autumn 1934 and later explosion (believed to be an attack) in 1935 led Ishii to shut down Zhongma Fortress. He received the authorization to move to Pingfang, approximately 24 km (15 mi) south of Harbin, to set up a new and much larger facility.
In 1936, Hirohito authorized, by imperial decree, the expansion of this unit and its integration into the Kwantung Army as the Epidemic Prevention Department. It was divided at the same time into the “Ishii Unit” and “Wakamatsu Unit” with a base in Hsinking. From August 1940, all these units were known collectively as the “Epidemic Prevention and Water Purification Department of the Kwantung Army or “Unit 731” for short.
A special project code-named Maruta used human beings for experiments. Test subjects were gathered from the surrounding population and were sometimes referred to euphemistically as “logs” (maruta). This term originated as a joke on the part of the staff because the official cover story for the facility given to the local authorities was that it was a lumber mill. In an account by a man who worked as a “junior uniformed civilian employee” of the Japanese Army in Unit 731, the term Maruta came from German, meaning medical experiment, used in such contexts as, “How many logs fell?”
The test subjects were selected to give a wide cross section of the population and included common criminals, captured bandits and anti-Japanese partisans, political prisoners, and also people rounded up by the Kempetai for alleged “suspicious activities”. They included infants, the elderly, and pregnant women.
Prisoners of war were subjected to vivisection without anesthesia. Vivisections were performed on prisoners after infecting them with various diseases. Scientists performed invasive surgery on prisoners, removing organs to study the effects of disease on the human body. These were conducted while the patients were alive because it was feared that the decomposition process would affect the results. The infected and vivisected prisoners included men, women, children, and infants.
Prisoners had limbs amputated in order to study blood loss. Those limbs that were removed were sometimes re-attached to the opposite sides of the body. Some prisoners’ limbs were frozen and amputated, while others had limbs frozen then thawed to study the effects of the resultant untreated gangrene and rotting.
Some prisoners had their stomachs surgically removed and the esophagus reattached to the intestines. Parts of the brain, lungs, liver, etc. were removed from some prisoners.
In 2007, the Japanese army surgeon Ken Yuasa testified to the Japan Times that, “I was afraid during my first vivisection, but the second time around, it was much easier. By the third time, I was willing to do it.” He believes at least 1,000 people, including surgeons, were involved in vivisections over mainland China.
Germ warfare attacks
Prisoners were injected with inoculations of disease, disguised as vaccinations, to study their effects. To study the effects of untreated venereal diseases, male and female prisoners were deliberately infected with syphilis and gonorrhea, then studied.
Plague fleas, infected clothing, and infected supplies encased in bombs were dropped on various targets. The resulting cholera, anthrax, and plague were estimated to have killed around 400,000 Chinese civilians. Tularemia was tested on Chinese civilians.
Unit 731 and its affiliated units (Unit 1644 and Unit 100 among others) were involved in research, development, and experimental deployment of epidemic-creating biowarfare weapons in assaults against the Chinese populace (both civilian and military) throughout World War II. Plague-infested fleas, bred in the laboratories of Unit 731 and Unit 1644, were spread by low-flying airplanes upon Chinese cities, coastal Ningbo in 1940, and Changde, Hunan Province, in 1941. This military aerial spraying killed thousands of people with bubonic plague epidemics.
Human targets were used to test grenades positioned at various distances and in different positions. Flame throwers were tested on humans. Humans were tied to stakes and used as targets to test germ-releasing bombs, chemical weapons, and explosive bombs.
In other tests, subjects were deprived of food and water to determine the length of time until Death, placed into high-pressure chambers until Death, experimented upon to determine the relationship between temperature, burns, and human survival, placed into centrifuges and spun until Death, injected with animal blood, exposed to lethal doses of x-rays, subjected to various chemical weapons inside gas Chambers, injected with sea water to determine if it could be a substitute for saline, and burned or buried alive.
Japanese scientists performed tests on prisoners with plague, cholera, smallpox, botulism, and other diseases. This research led to the development of the defoliation bacilli bomb and the flea bomb used to spread the bubonic plague. Some of these bombs were designed with ceramic (porcelain) shells, an idea proposed by Ishii in 1938.
These bombs enabled Japanese soldiers to launch biological attacks, infecting agriculture, reservoirs, wells, and other areas with anthrax, plague-carrier fleas, typhoid, dysentery, cholera, and other deadly pathogens. During biological bomb experiments, scientists dressed in protective suits would examine the dying victims. Infected food supplies and clothing were dropped by airplane into areas of China not occupied by Japanese forces. In addition, poisoned food and candies were given out to unsuspecting victims and children, and the results examined.
In 2002, Changde, China, site of the flea spraying attack, held an “International Symposium on the Crimes of Bacteriological Warfare” which estimated that at least 580,000 people died as a result of the attack. The historian Sheldon Harris claims that 200,000 died. In addition to Chinese casualties, 1,700 Japanese in Chekiang were killed by their own biological weapons while attempting to unleash the biological agent, which evidences serious issues with distribution.
Known unit members
- Lieutenant General Shirō Ishii
- Lieutenant Colonel Ryoichi Naito, founder of the pharmaceutical company Green Cross
- Masaji Kitano
- Yoshio Shinozuka
- Yasuji Kaneko
Unit 731 was divided into eight divisions:
- Division 1: Research on bubonic plague, cholera, anthrax, typhoid and tuberculosis using live human subjects. For this purpose, a prison was constructed to contain around three to four hundred people.
- Division 2: Research for biological weapons used in the field, in particular the production of devices to spread germs and parasites.
- Division 3: Production of shells containing biological agents. Stationed in Harbin.
- Division 4: Production of other miscellaneous agents.
- Division 5: Training of personnel.
- Divisions 6–8: Equipment, medical and administrative units.
One of the buildings is open to visitors The Unit 731 complex covered six square kilometers and consisted of more than 150 buildings. The design of the facilities made them hard to destroy by bombing. The complex contained various factories. It had around 4,500 containers to be used to raise fleas, six cauldrons to produce various chemicals, and around 1,800 containers to produce biological agents. Approximately 30 kg of bubonic plague bacteria could be produced in several days.
Some of Unit 731’s satellite facilities are in use by various Chinese industrial concerns. A portion has been preserved and is open to visitors as a War Crimes Museum.
A medical school and research facility belonging to Unit 731 operated in the Shinjuku District of Tokyo during World War II. In 2006, Toyo Ishii, a nurse who worked at the school during the war, revealed that she had helped bury bodies and pieces of bodies on the school’s grounds shortly after Japan’s surrender in 1945. In response, in February 2011 the Ministry of Health began to excavate the site.
China requested DNA samples from any human remains discovered at the site. The Japanese government, which has never officially acknowledged the existence of Unit 731—rejected the request.
The related Unit 8604 was operated by the Japanese Southern China Area Army and stationed at Canton (Guangzhou). This installation conducted human experimentation in food and water deprivation as well as water-borne typhus. According to postwar testimony, this facility served as the main rat breeding farm for the medical units to provide them with bubonic plague vectors for experiments.
Unit 731 was part of the Epidemic Prevention and Water Purification Department which dealt with contagious disease and water supply generally.
Mukden POW camp
According to Maj. Robert Peaty, of the Royal Army Ordnance Corps, who was the senior British officer at Mukden, a prisoner-of-war camp 350 miles from Pingfan, doctors from Unit 731 administered the regular injections of infectious diseases, disguised as harmless vaccinations, which eventually killed 186 Americans.
Surrender and immunity
Information sign at the site today. Operations and experiments continued until the end of the war. Ishii had wanted to use biological weapons in the Pacific conflict since May 1944, but his attempts were repeatedly snubbed.
Destruction of evidence
With the Russian invasion of Manchukuo and Mengjiang in August 1945, the unit had to abandon their work in haste. The members and their families fled to Japan.
Ishii ordered every member of the group “to take the secret to the grave”, threatening to find them if they failed, and prohibiting any of them from going into public work back in Japan. Potassium cyanide vials were issued for use in the event that the remaining personnel were captured.
Skeleton crews of Ishii’s Japanese troops blew the compound up in the final days of the war to destroy evidence of their activities, but most were so well constructed that they survived somewhat intact.
American grant of immunity
After Imperial Japan surrendered to the Allies in 1945, Douglas MacArthur became the Supreme Commander of the Allied Powers, rebuilding Japan during the Allied occupation. MacArthur secretly granted immunity to the physicians of Unit 731, including their leader, in exchange for providing America, but not the other wartime allies, with their research on biological warfare. American occupation authorities monitored the activities of former unit members, including reading and censoring their mail. The U.S. believed that the research data was valuable. The U.S. did not want other nations, particularly the Soviet Union, to acquire data on biological weapons.
The Tokyo War Crimes Tribunal heard only one reference to Japanese experiments with “poisonous serums” on Chinese civilians. This took place in August 1946 and was instigated by David Sutton, assistant to the Chinese prosecutor. The Japanese defense counselor argued that the claim was vague and uncorroborated and it was dismissed by the tribunal president, Sir William Webb, for lack of evidence. The subject was not pursued further by Sutton, who was likely aware of Unit 731’s activities. His reference to it at the trial is believed to have been accidental.
Separate Soviet trials
Although publicly silent on the issue at the Tokyo Trials, the Soviet Union pursued the case and prosecuted twelve top military leaders and scientists from Unit 731 and its affiliated biological-war prisons Unit 1644 in Nanjing, and Unit 100 in Changchun, in the Khabarovsk War Crime Trials. Included among those prosecuted for war crimes including germ warfare was General Otozō Yamada, the commander-in-chief of the million-man Kwantung Army occupying Manchuria.
The trial of those captured Japanese perpetrators was held in Khabarovsk in December 1949. A lengthy partial transcript of the trial proceedings was published in different languages the following year by a Moscow foreign languages press, including an English language edition. The lead prosecuting attorney at the Khabarovsk trial was Lev Smirnov, who had been one of the top Soviet prosecutors at the Nuremberg Trials. The Japanese doctors and army commanders who had perpetrated the Unit 731 experiments received sentences from the Khabarovsk court ranging from two to 25 years in a Siberian labor camp. The Americans refused to acknowledge the trials, branding them communist propaganda.
After World War II, the Soviet Union built a biological weapons facility in Sverdlovsk using documentation captured from Unit 731 in Manchuria.
After World War II
Official silence under Occupation
As above, under the American occupation the members of Unit 731 and other experimental units were allowed to go free. One graduate of Unit 1644, Masami Kitaoka, continued to do experiments on unwilling Japanese subjects from 1947 to 1956 while working for the National Institute of Health Sciences. He infected prisoners with rickettsia and mental health patients with typhus.
Post-Occupation Japanese media coverage and debate
Japanese discussions of Unit 731’s activity began in the 1950s, after the end of the American occupation of Japan. In 1952, human experiments carried out in Nagoya City Pediatric Hospital, which resulted in 1 death, were publicly tied to former members of Unit 731. Later in that decade, journalists suspected that the murders attributed by the government to Sadamichi Hirasawa were actually carried out by members of Unit 731. In 1958, Japanese author Shusaku Endo published the book The Sea and Poison about human experimentation, which is thought to have been based on a real incident.
The author Morimura Seiichi published the book The Devil’s Gluttony in 1981, followed by The Devil’s Gluttony: A Sequel in 1983. This purported to reveal the “true” operations of Unit 731, but actually confused them with that of Unit 100, and falsely used unrelated photos attributing them to Unit 731, which raised questions about its accuracy.
Also in 1981 appeared the first direct testimony of human vivisection in China, by Ken Yuasa. Since then many more in-depth testimonies have appeared in Japanese. The 2001 documentary Japanese Devils was composed largely of interviews with 14 members of Unit 731 who had been taken as prisoners by China and later released.
Official government response in Japan
Since the end of the US Occupation, the Japanese government has repeatedly apologized for its prewar behavior in general, but specific apologies and indemnities are determined on the basis of bilateral determination that crimes occurred, which requires a high standard of evidence. Unit 731 presents a special problem, since unlike Nazi human experimentation which is extremely well documented, the activities of Unit 731 are known only from the testimonies of former unit members, and testimony cannot be employed to determine indemnity in this way.
Japanese history textbooks usually contain references to Unit 731, but do not go into detail about allegations, in accordance with this principle. Saburo Ienaga’s New History of Japan included a detailed description, based on officers’ testimony. The Ministry for Education attempted to remove this passage from his textbook before it was taught in public schools, on the basis that the testimony was insufficient. The Supreme Court of Japan ruled in 1997 that the testimony was indeed sufficient and that requiring it to be removed was an illegal violation of freedom of speech.
In 1997, the international lawyer Kōnen Tsuchiya filed a class action suit against the Japanese government demanding reparations for the actions of Unit 731, using evidence filed by Rikkyo University professor Makoto Ueda. All court levels found that the suit was baseless. No findings of fact were made about the existence of human experimentation, but the decision of the court was that reparations are determined by international treaties and not by local court cases.
In October 2003, the Prime Minister of Japan responded to an inquiry from a member of the House of Representatives of Japan stating that, while the current Japanese government does not possess any records related to Unit 731, they recognize the gravity of the matter and will publicize any records that are located in the future.