Unit 731

Unit Tōgō was set into motion in the Zhongma Fortress, a prison and experimentation camp in Beiyinhe, a village 100 kilometers (62 mi) south of Harbin on the South Manchuria Railway. The prisoners brought to Zhongma included common criminals, captured bandits, anti-Japanese partisans, as well as political prisoners and people rounded up on trumped up charges by the Kempeitai. Prisoners were generally well fed on a diet of rice or wheat, meat, fish, and occasionally even alcohol in order to be in normal health at the beginning of experiments. Then, over several days, prisoners were eventually drained of blood and deprived of nutrients and water. Their deteriorating health was recorded. Some were also vivisected. Others were deliberately infected with plague bacteria and other microbes.[14]

A prison break in the autumn of 1934, which jeopardized the facility's secrecy, and an explosion in 1935 (believed to be sabotage) led Ishii to shut down Zhongma Fortress. He then received authorization to move to Pingfang, approximately 24 kilometers (15 mi) south of Harbin, to set up a new, much larger facility.[15]

Close-up photo of the Unit 731 main "square building" taken by Unit 731's aviation and photography class in 1940

In 1936, Emperor Hirohito issued a decree authorizing the expansion of the unit and its integration into the Kwantung Army as the Epidemic Prevention Department.[16] It was divided at that time into the "Ishii Unit" and "Wakamatsu Unit", with a base in Hsinking. From August 1940 on, the units were known collectively as the "Epidemic Prevention and Water Purification Department of the Kwantung Army" (關（くわん）東（とう）軍（ぐん）防（ばう）疫（えき）給（きふ）水（すゐ）部（ぶ）本（ほん）部（ぶ）) or "Unit 731" (滿（まん）洲（しゆう）第（だい）７（なな）３（さん）１（いち）部（ぶ）隊（たい）) for short.[17]

His younger brother, Prince Mikasa, toured the Unit 731 headquarters in China, and wrote in his memoir that he watched films showing how Chinese prisoners were "made to march on the plains of Manchuria for poison gas experiments on humans."[1]

Hideki Tojo, who later became Prime Minister in 1941, was also shown films of the experiments, which he described as "unpleasant."[18]

In addition to the establishment of Unit 731, the decree also called for the creation of an additional biological warfare development unit, called the Kwantung Army Military Horse Epidemic Prevention Workshop (later referred to as Manchuria Unit 100), and a chemical warfare development unit called the Kwantung Army Technical Testing Department (later referred to as Manchuria Unit 516). After the Japanese invasion of China in 1937, sister chemical and biological warfare units were founded in major Chinese cities and were referred to as Epidemic Prevention and Water Supply Units. Detachments included Unit 1855 in Beijing, Unit Ei 1644 in Nanjing, Unit 8604 in Guangzhou, and later Unit 9420 in Singapore. All of these units comprised Ishii's network, which, at its height in 1939, oversaw over 10,000 personnel.[19] Medical doctors and professors from Japan were attracted to join Unit 731 both by the rare opportunity to conduct human experimentation and the Army's strong financial backing.[20]

Thousands of men, women, children, and infants interned at prisoner of war camps were subjected to vivisection, often performed without anesthesia and usually lethal.[28][29] In a video interview, former Unit 731 member Okawa Fukumatsu admitted to having vivisected a pregnant woman.[30] Vivisections were performed on prisoners after infecting them with various diseases. Researchers performed invasive surgery on prisoners, removing organs to study the effects of disease on the human body.[31]

Human dissection experiment room

Prisoners had limbs amputated in order to study blood loss. Limbs removed were sometimes reattached to the opposite side of victims' bodies. Some prisoners had their stomachs surgically removed and their esophagus reattached to the intestines. Parts of organs, such as the brain, lungs, and liver, were removed from others.[29] Imperial Japanese Army surgeon Ken Yuasa suggests that practising vivisection on human subjects was widespread even outside Unit 731,[32] estimating that at least 1,000 Japanese personnel were involved in the practice in mainland China.[33] Yuasa said that when he performed vivisections on captives, they were "all for practice rather than for research," and that such practises were "routine" among Japanese doctors stationed in China during the war.[22]

The New York Times interviewed a former member of Unit 731. Insisting on anonymity, the former Japanese medical assistant recounted his first experience in vivisecting a live human being, who had been deliberately infected with the plague, for the purpose of developing "plague bombs" for war.

"The fellow knew that it was over for him, and so he didn't struggle when they led him into the room and tied him down, but when I picked up the scalpel, that's when he began screaming. I cut him open from the chest to the stomach, and he screamed terribly, and his face was all twisted in agony. He made this unimaginable sound, he was screaming so horribly. But then finally he stopped. This was all in a day's work for the surgeons, but it really left an impression on me because it was my first time."[34]

Other sources suggest that it was the usual practice in the Unit for surgeons to stuff a rag (or medical gauze) into the mouth of prisoners before commencing vivisection in order to stifle any screaming.[35]

Ruins of a boiler building at the Unit 731 bioweapons facility

Unit 731 and its affiliated units (Unit 1644 and Unit 100, among others) were involved in research, development and experimental deployment of epidemic-creating biological weapons in assaults against the Chinese populace (both military and civilian) throughout World War II. Plague-infected fleas, bred in the laboratories of Unit 731 and Unit 1644, were spread by low-flying airplanes over Chinese cities, including coastal Ningbo and Changde, Hunan Province, in 1940 and 1941.[5] These operations killed tens of thousands with bubonic plague epidemics. An expedition to Nanjing involved spreading typhoid and paratyphoid germs into the wells, marshes, and houses of the city, as well as infusing them in snacks distributed to locals. Epidemics broke out shortly after, to the elation of many researchers, who concluded that paratyphoid fever was "the most effective" of the pathogens.[36][37]^{: xii, 173}

At least 12 large-scale bioweapon field trials were carried out, and at least 11 Chinese cities attacked with biological agents. An attack on Changde in 1941 reportedly led to approximately 10,000 biological casualties and 1,700 deaths among ill-prepared Japanese troops, in most cases due to cholera.[4] Japanese researchers performed tests on prisoners with bubonic plague, cholera, smallpox, botulism, and other diseases.[38] This research led to the development of the defoliation bacilli bomb and the flea bomb used to spread bubonic plague.[39] Some of these bombs were designed with porcelain shells, an idea proposed by Ishii in 1938.

These bombs enabled Japanese soldiers to launch biological attacks, infecting agriculture, reservoirs, wells, as well as other areas, with anthrax- and plague-carrier fleas, typhoid, cholera, or other deadly pathogens. During biological bomb experiments, researchers 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 candy were given to unsuspecting victims. 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 at least 400,000 Chinese civilians.[40] Tularemia was also tested on Chinese civilians.[41]

Due to pressure from numerous accounts of the biowarfare attacks, Chiang Kai-shek sent a delegation of army and foreign medical personnel in November 1941 to document evidence and treat the afflicted. A report on the Japanese use of plague-infected fleas on Changde was made widely available the following year but was not addressed by the Allied Powers until Franklin D. Roosevelt issued a public warning in 1943 condemning the attacks.[42][43]

In December 1944, the Japanese Navy explored the possibility of attacking cities in California with biological weapons, known as Operation PX or Operation Cherry Blossoms at Night. The plan for the attack involved Seiran aircraft launched by submarine aircraft carriers upon the West Coast of the United States—specifically, the cities of San Diego, Los Angeles, and San Francisco. The planes would spread weaponized bubonic plague, cholera, typhus, dengue fever, and other pathogens in a biological terror attack upon the population. The submarine crews would infect themselves and run ashore in a suicide mission.[44][45][46][47] Planning for Operation PX was finalized on March 26, 1945, but shelved shortly thereafter due to the strong opposition of Chief of General Staff Yoshijirō Umezu. Umezu later explained his decision as such: "If bacteriological warfare is conducted, it will grow from the dimension of war between Japan and America to an endless battle of humanity against bacteria. Japan will earn the derision of the world."[48]

Human targets were used to test grenades positioned at various distances and in various positions. Flamethrowers were tested on people.[49] Victims were also tied to stakes and used as targets to test pathogen-releasing bombs, chemical weapons, shrapnel bombs with varying amounts of fragments, and explosive bombs as well as bayonets and knives.

To determine the best course of treatment for varying degrees of shrapnel wounds sustained on the field by Japanese Soldiers, Chinese prisoners were exposed to direct bomb blasts. They were strapped, unprotected, to wooden planks that were staked into the ground at increasing distances around a bomb that was then detonated. It was surgery for most, autopsies for the rest.

— Unit 731, Nightmare in Manchuria[50][51]

In other tests, subjects were deprived of food and water to determine the amount of time until death; placed into low-pressure chambers until their eyes popped from the sockets; experimented upon to determine the relationship between temperature, burns, and human survival; hung upside down until death; crushed with heavy objects; electrocuted; dehydrated with hot fans;[52] placed into centrifuges and spun until death; injected with animal blood, notably with horse blood; exposed to lethal doses of X-rays; subjected to various chemical weapons inside gas chambers; injected with seawater; and burned or buried alive.[53][54] In addition to chemical agents, the properties of many different toxins were also investigated by the Unit. To name a few, prisoners were exposed to tetrodotoxin (pufferfish or fugu venom), heroin, Korean bindweed, bactal, and castor-oil seeds (ricin).[55][56] Massive amounts of blood were drained from some prisoners in order to study the effects of blood loss according to former Unit 731 vivisectionist Okawa Fukumatsu. In one case, at least half a liter of blood was drawn at two-to-three-day intervals.[57]

As stated above, dehydration experiments were performed on the victims. The purpose of these tests was to determine the amount of water in an individual's body and to see how long one could survive with a very low to no water intake. It is known that victims were also starved before these tests began. The deteriorating physical states of these victims were documented by staff at a periodic interval.

"It was said that a small number of these poor men, women, and children who became marutas were also mummified alive in total dehydration experiments. They sweated themselves to death under the heat of several hot dry fans. At death, the corpses would only weigh ≈1/5 normal bodyweight."

— Hal Gold, Japan's Infamous Unit 731, (2019)

Unit 731 also performed transfusion experiments with different blood types. Unit member Naeo Ikeda wrote:

In my experience, when A type blood 100 cc was transfused to an O type subject, whose pulse was 87 per minute and temperature was 35.4 degrees C, 30 minutes later the temperature rose to 38.6 degrees with slight trepidation. Sixty minutes later the pulse was 106 per minute and the temperature was 39.4 degrees. Two hours later the temperature was 37.7 degrees, and three hours later the subject recovered. When AB type blood 120 cc was transfused to an O type subject, an hour later the subject described malaise and psychroesthesia in both legs. When AB type blood 100 cc was transfused to a B type subject, there seemed to be no side effect.

— Man, Medicine, and the State: The Human Body as an Object of Government Sponsored Medical Research in the 20th Century (2006) pp. 38–39

Unit 731 tested many different chemical agents on prisoners and had a building dedicated to gas experiments. Some of the agents tested were mustard gas, lewisite, cyanic acid gas, white phosphorus, adamsite, and phosgene gas.[58] A former army major and technician gave the following testimony anonymously (at the time of the interview, this man was a professor emeritus at a national university):

In 1943, I attended a poison gas test held at the Unit 731 test facilities. A glass-walled chamber about three meters square [97 sq ft] and two meters [6.6 ft] high was used. Inside of it, a Chinese man was blindfolded, with his hands tied around a post behind him. The gas was adamsite (sneezing gas), and as the gas filled the chamber the man went into violent coughing convulsions and began to suffer excruciating pain. More than ten doctors and technicians were present. After I had watched for about ten minutes, I could not stand it any more, and left the area. I understand that other types of gasses were also tested there.

— Hal Gold, Japan's Infamous Unit 731, p. 349 (2019)

Takeo Wano, a former medical worker in Unit 731, said that he saw a Western man, who was vertically cut into two pieces, pickled in a jar of formaldehyde.[59] Wano guessed that the man was Russian because there were many Russians living in the area at that time.[59]

Unit 100 also experimented with toxic gas. Phone booth-like tanks were used as portable gas chambers for the prisoners. Some were forced to wear various types of gas masks; others wore military uniforms, and some wore no clothes at all.

Some of the tests have been described as "psychopathically sadistic, with no conceivable military application." For example, one experiment documented the time it took for three-day-old babies to freeze to death.[60][61]

Unit 731 also tested chemical weapons on prisoners in field conditions. A report authored by unknown researcher in the Kamo Unit (Unit 731) describes a large human experiment of yperite gas (mustard gas) on 7–10 September 1940. Twenty subjects were divided into three groups and placed in combat emplacements, trenches, gazebos, and observatories. One group was clothed with Chinese underwear, no hat, and no mask and was subjected to as much as 1,800 field gun rounds of yperite gas over 25 minutes. Another group was clothed in summer military uniform and shoes; three had masks and another three had no mask. They also were exposed to as much as 1,800 rounds of yperite gas. A third group was clothed in summer military uniform, three with masks and two without masks, and were exposed to as much as 4,800 rounds. Then their general symptoms and damage to skin, eye, respiratory organs, and digestive organs were observed at 4 hours, 24 hours, and 2, 3, and 5 days after the shots. Injecting the blister fluid from one subject into another subject and analyses of blood and soil were also performed. Five subjects were forced to drink a solution of yperite and lewisite gas in water, with or without decontamination. The report describes conditions of every subject precisely without mentioning what happened to them in the long run.[62] The following is an excerpt of one of these reports:

Number 376, dugout of the first area:

September 7, 1940, 6 pm: Tired and exhausted. Looks with hollow eyes. Weeping redness of the skin of the upper part of the body. Eyelids edematous, swollen. Epiphora. Hyperemic conjunctivae.

September 8, 6 am: Neck, breast, upper abdomen and scrotum weeping, reddened, swollen. Covered with millet-seed-size to bean-size blisters. Eyelids and conjunctivae hyperemic and edematous. Had difficulties opening the eyes.

September 8, 6 pm: Tired and exhausted. Feels sick. Body temperature 37 degrees Celsius. Mucous and bloody erosions across the shoulder girdle. Abundant mucous nose secretions. Abdominal pain. Mucous and bloody diarrhea. Proteinuria.

September 9, 7 am: Tired and exhausted. Weakness of all four extremities.

Low morale. Body temperature 37 degrees Celsius. Skin of the face still weeping.

— Man, Medicine, and the State: The Human Body as an Object of Government Sponsored Medical Research in the 20th Century (2006) p. 187

Army Engineer Hisato Yoshimura conducted experiments by taking captives outside, dipping various appendages into water of varying temperatures, and allowing the limb to freeze.[63] Once frozen, Yoshimura would strike their affected limbs with a short stick, "emitting a sound resembling that which a board gives when it is struck."[59] Ice was then chipped away, with the affected area being subjected to various treatments, such as being doused in water, exposed to the heat of fire, etc.

Members of the Unit referred to Yoshimura as a "scientific devil" and a "cold-blooded animal" because he would conduct his work with strictness.[64] Naoji Uezono, a member of Unit 731, described in a 1980s interview a grisly scene where Yoshimura had "two naked men put in an area 40–50 degrees below zero and researchers filmed the whole process until [the subjects] died. [The subjects] suffered such agony they were digging their nails into each other's flesh."[65] Yoshimura's lack of remorse was evident in an article he wrote for the Journal Of Japanese Physiology in 1950 in which he admitted to using 20 children and a three-day-old infant in experiments which exposed them to zero-degree-Celsius ice and salt water.[66] Although this article drew criticism, Yoshimura denied any guilt when contacted by a reporter from the Mainichi Shimbun.[67][68] Yoshimura developed a "resistance index of frostbite" based on the mean temperature 5 to 30 minutes after immersion in freezing water, the temperature of the first rise after immersion, and the time until the temperature first rises after immersion. In a number of separate experiments it was then determined how these parameters depend on the time of day a victim's body part was immersed in freezing water, the surrounding temperature and humidity during immersion, how the victim had been treated before the immersion ("after keeping awake for a night", "after hunger for 24 hours", "after hunger for 48 hours", "immediately after heavy meal", "immediately after hot meal", "immediately after muscular exercise", "immediately after cold bath", "immediately after hot bath"), what type of food the victim had been fed over the five days preceding the immersions with regard to dietary nutrient intake ("high protein (of animal nature)", "high protein (of vegetable nature)", "low protein intake", and "standard diet"), and salt intake (45 g NaCl per day, 15 g NaCl per day, no salt).[69] This original data is seen in the attached figure.

Scan of Yoshimura Hisato's frostbite research data

Unit members orchestrated forced sex acts between infected and non-infected prisoners to transmit the disease, as the testimony of a prison guard on the subject of devising a method for transmission of syphilis between patients shows:

Infection of venereal disease by injection was abandoned, and the researchers started forcing the prisoners into sexual acts with each other. Four or five unit members, dressed in white laboratory clothing completely covering the body with only eyes and mouth visible, rest covered, handled the tests. A male and female, one infected with syphilis, would be brought together in a cell and forced into sex with each other. It was made clear that anyone resisting would be shot.[70]

After victims were infected, they were vivisected at different stages of infection, so that internal and external organs could be observed as the disease progressed. Testimony from multiple guards blames the female victims as being hosts of the diseases, even as they were forcibly infected. Genitals of female prisoners that were infected with syphilis were called "jam-filled buns" by guards.[71]

Some children grew up inside the walls of Unit 731, infected with syphilis. A Youth Corps member deployed to train at Unit 731 recalled viewing a batch of subjects that would undergo syphilis testing: "one was a Chinese woman holding an infant, one was a White Russian woman with a daughter of four or five years of age, and the last was a White Russian woman with a boy of about six or seven."[71] The children of these women were tested in ways similar to their parents, with specific emphasis on determining how longer infection periods affected the effectiveness of treatments.

Female prisoners were forced to become pregnant for use in experiments. The hypothetical possibility of vertical transmission (from mother to child) of diseases, particularly syphilis, was the stated reason for the torture. Fetal survival and damage to mother's reproductive organs were objects of interest. Though "a large number of babies were born in captivity," there have been no accounts of any survivors of Unit 731, children included. It is suspected that the children of female prisoners were killed after birth or aborted.[71]

While male prisoners were often used in single studies, so that the results of the experimentation on them would not be clouded by other variables, women were sometimes used in bacteriological or physiological experiments, sex experiments, and as the victims of sex crimes. The testimony of a unit member that served as a guard graphically demonstrated this reality:

One of the former researchers I located told me that one day he had a human experiment scheduled, but there was still time to kill. So he and another unit member took the keys to the cells and opened one that housed a Chinese woman. One of the unit members raped her; the other member took the keys and opened another cell. There was a Chinese woman in there who had been used in a frostbite experiment. She had several fingers missing and her bones were black, with gangrene set in. He was about to rape her anyway, then he saw that her sex organ was festering, with pus oozing to the surface. He gave up the idea, left and locked the door, then later went on to his experimental work.[71]

Despite the prison's status as a highly secure building, at least one unsuccessful escape attempt did occur. Corporal Kikuchi Norimitsu testified that he was told by another unit member that a prisoner "had shown violence and had struck the experimenter with a door handle" and then "jumped out of the cell and ran down the corridor, seized the keys and opened the iron doors and some of the cells. Some of the prisoners managed to jump out but these were only the bold ones. These bold ones were shot."[94]

Seiichi Morimura in his book The Devil's Feast went into some greater detail regarding this escape attempt. Two Russian male prisoners were in a cell with handcuffs on, one of them lay flat on the floor pretending to be sick. This got the attention of a staff member who saw it as an unusual condition. That staff member decided to enter the cell. The Russian lying on the floor suddenly sprang up and knocked the guard down. The two Russians opened their handcuffs, took the keys, and opened some other cells while yelling. Some prisoners, including Russian and Chinese, were frantically roaming the corridors and kept yelling and shouting. One Russian shouted to the members of Unit 731, demanding to be shot rather than used as an experimental object. This Russian was shot to death.[95] One staff member, who was an eyewitness at this escape attempt, recalled: "spiritually we were all lost in front of the 'marutas' who had no freedom and no weapons. At that time we understood in our hearts that justice was not on our side."[95]

Unfortunately for the prisoners of Unit 731, escape was an impossibility. Even if they had managed to escape the quadrangle (itself a heavily fortified building full of staff), they would have had to get over a three-meter-high (9.8 ft) brick wall surrounding the complex, and then across a dry moat filled with electrified wire running around the perimeter of the complex.[96]

Members of Unit 731 were not immune from being subjects of experiments. Yoshio Tamura, an assistant in the Special Team, recalled that Yoshio Sudō, an employee of the first division at Unit 731, became infected with bubonic plague as a result of the production of plague bacteria. The Special Team was then ordered to vivisect Sudō. Tamura recalled:

Sudō had, a few days previously, been interested in talking about women, but now he was thin as a rake, with many purple spots over his body. A large area of scratches on his chest were bleeding. He painfully cried and breathed with difficulty. I sanitised his whole body with disinfectant. Whenever he moved, a rope around his neck tightened. After Sudō's body was carefully checked [by the surgeon], I handed a scalpel to [the surgeon] who, reversely gripping the scalpel, touched Sudō's stomach skin and sliced downward. Sudō shouted "brute!" and died with this last word.

— Criminal History of Unit 731 of the Japanese Military, pp. 118–119 (1991)

Additionally, Unit 731 Youth Corps member Yoshio Shinozuka testified that his friend junior assistant Mitsuo Hirakawa was vivisected as a result of being accidentally infected with plague.[62]

Unit 731 had branches in Linkou (Branch 162), Mudanjiang, Hailin (Branch 643), Sunwu (Branch 673), Toan, and Hailar (Branch 543).[3]^{: 60, 84, 124, 310}

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.[101]

While Tokyo courts acknowledged in 2002 that Unit 731 has been involved in biological warfare research, as of 2011 the Japanese government had made no official acknowledgment of the atrocities committed against test subjects and rejected the Chinese government's requests for DNA samples to identify human remains (including skulls and bones) found near an army medical school.[102]

At Tokyo's Kyushu Imperial University in 1945, US POWs from a shot down B-29 were subjected to fatal medical experimentation.[103]

The Unit 731 square building during its demolition in 1945

As the Second World War started to come to an end, all prisoners within the compound were killed to conceal evidence, and there were no documented survivors.[104] With the coming of the Red Army in August 1945, the unit had to abandon their work in haste. Ministries in Tokyo ordered the destruction of all incriminating materials, including those in Pingfang. Potential witnesses, such as the 300 remaining prisoners, were either gassed or fed poison while the 600 Chinese and Manchurian laborers were shot. Ishii ordered every member of the group to disappear and "take the secret to the grave."[105] Potassium cyanide vials were issued for use in case the remaining personnel were captured.

Skeleton crews of Ishii's Japanese troops blew up the compound in the final days of the war to destroy evidence of their activities, but many were sturdy enough to remain somewhat intact.

Among the individuals in Japan after its 1945 surrender was Lieutenant Colonel Murray Sanders, who arrived in Yokohama via the American ship Sturgess in September 1945. Sanders was a highly regarded microbiologist and a member of America's military center for biological weapons. Sanders' duty was to investigate Japanese biological warfare activity. At the time of his arrival in Japan, he had no knowledge of what Unit 731 was.[71] Until Sanders finally threatened the Japanese with bringing the Soviets into the picture, little information about biological warfare was being shared with the Americans. The Japanese wanted to avoid prosecution under the Soviet legal system, so, the morning after he made his threat, Sanders received a manuscript describing Japan's involvement in biological warfare.[106] Sanders took this information to General Douglas MacArthur, who was the Supreme Commander of the Allied Powers and responsible for rebuilding Japan during the Allied occupations. MacArthur struck a deal with Japanese informants:[107] he secretly granted immunity to the physicians of Unit 731, including their leader, in exchange for providing America solely, with their research on biological warfare and data from human experimentation.[6] American occupation authorities monitored the activities of former unit members, including reading and censoring their mail.[108] The Americans believed that the research data was valuable and did not want other nations, particularly the Soviet Union, to acquire data on biological weapons.[109]

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 counsel 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 probably unaware of Unit 731's activities. His reference to it at the trial is believed to have been accidental. Later in 1981, one of the last surviving members of the Tokyo Tribunal, Judge Röling, had expressed bitterness in not being made aware of the suppression of evidence of Unit 731 and wrote, "It is a bitter experience for me to be informed now that centrally ordered Japanese war criminality of the most disgusting kind was kept secret from the court by the U.S. government."[110]

While German physicians were brought to trial and had their crimes publicized, the U.S. concealed information about Japanese biological warfare experiments and secured immunity for the perpetrators.[111] Critics argue that racism led to the double standard in the American postwar responses to the experiments conducted on different nationalities.[111] Whereas the perpetrators of Unit 731 were exempt from prosecution, the U.S. held a tribunal in Yokohama in 1948 that indicted nine Japanese physician professors and medical students for conducting vivisection upon captured American pilots; two professors were sentenced to death and others to 15–20 years' imprisonment.[111]

Although publicly silent on the issue at the Tokyo Trials, the Soviet Union pursued the case and prosecuted 12 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 crimes trials. Among those accused of war crimes, including germ warfare, was General Otozō Yamada, commander-in-chief of the million-man Kwantung Army occupying Manchuria.

The trial of the Japanese perpetrators was held in Khabarovsk in December 1949; a lengthy partial transcript of trial proceedings was published in different languages the following year by the Moscow foreign languages press, including an English-language edition.[112] 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 2 to 25 years in a Siberian labor camp. The United States refused to acknowledge the trials, branding them communist propaganda.[113] The sentences doled out to the Japanese perpetrators were unusually lenient by Soviet standards, and all but two of the defendants returned to Japan by the 1950s (with one prisoner dying in prison and the other committing suicide inside his cell).

In addition to the accusations of propaganda, the US also asserted that the trials were to only serve as a distraction from the Soviet treatment of several hundred thousand Japanese prisoners of war; meanwhile, the USSR asserted that the US had given the Japanese diplomatic leniency in exchange for information regarding their human experimentation. The accusations of both the US and the USSR were true, and it is believed that the Japanese had also given information to the Soviets regarding their biological experimentation for judicial leniency.[114] This was evidenced by the Soviet Union building a biological weapons facility in Sverdlovsk using documentation captured from Unit 731 in Manchuria.[115]

As above, during the United States occupation of Japan, the members of Unit 731 and the members of other experimental units were allowed to go free. On 6 May 1947, Douglas MacArthur, the Supreme Commander of the Allied Forces, wrote to Washington in order to inform it that "additional data, possibly some statements from Ishii, can probably be obtained by informing Japanese involved that information will be retained in intelligence channels and will not be employed as 'war crimes' evidence".[6]

According to an investigation by The Guardian, after the end of the war, under the pretense of vaccine development, former members of Unit 731 conducted human experiments on Japanese prisoners, babies and mental patients, with secret funding from the American Government.[116] One graduate of Unit 1644, Masami Kitaoka, continued to perform experiments on unwilling Japanese subjects from 1947 to 1956. He performed his experiments while he was working for Japan's National Institute of Health Sciences. He infected prisoners with rickettsia and infected mentally-ill patients with typhus.[117] As the chief of the unit, Shiro Ishii was granted immunity from prosecution for war crimes by the American occupation authorities, because he had provided human experimentation research materials to them. From 1948 to 1958, less than five percent of the documents were transferred onto microfilm and stored in the US National Archives before they were shipped back to Japan.[118]

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 one death, were publicly tied to former members of Unit 731.[119] 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 Shūsaku Endō published the book The Sea and Poison about human experimentation in Fukuoka, which is thought to have been based on a real incident.

The author Seiichi Morimura published The Devil's Gluttony (悪魔の飽食) in 1981, followed by The Devil's Gluttony: A Sequel in 1983. These books purported to reveal the "true" operations of Unit 731, but falsely attributed unrelated photos to the Unit, which raised questions about their accuracy.[120][121]

Also in 1981, the first direct testimony of human vivisection in China was given by Ken Yuasa. Since then, much more in depth testimony has been given in Japan. The 2001 documentary Japanese Devils largely consists of interviews with fourteen Unit 731 staff members taken prisoner by China and later released.[122]

Japanese biological warfare operations were by far the largest during WWII, and "possibly with more people and resources than the BW producing nations of France, Hungary, Italy, Poland, and the Soviet Union combined, between the world wars.[123] Despite the apparent success, Unit 731 lacked adequate scientific and engineering foundations to further maximize its effectiveness..[124][125] Harris speculated that US scientists generally wanted to acquire it due to the concept of forbidden fruit, believing that lawful and ethical prohibitions could affect the outcomes of their research.[126]

During the COVID-19 pandemic, some scientists called for experimental data from Unit 731 to be publicly released to the international medical community because the data available on human-pathogen interactions could have helped epidemiologists with pandemic control.[127] The information has been withheld by both the US and Japanese government.

In 1983, the Japanese Ministry of Education asked Japanese historian Saburō Ienaga to remove a reference from one of his textbooks that stated Unit 731 conducted experiments on thousands of Chinese. The ministry alleged that no academic research supported the claim. In 1984, Japanese historian Tsuneishi Keiichi translated and published over 4,000 pages of U.S. documents on Japanese biological warfare. The ministry backed down after new studies were published in Japan and important evidence surfaced in the United States.[128]

Japanese history textbooks usually contain references to Unit 731, but do not go into detail about allegations, in accordance with this principle.[129][130] Saburō 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.[131]

In 1997, 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 Professor Makoto Ueda of Rikkyo University. All levels of the Japanese court system found the suit baseless. No findings of fact were made about the existence of human experimentation, but the courts' ruling was that reparations are determined by international treaties, not national courts.

In August 2002, the Tokyo district court ruled for the first time that Japan had engaged in biological warfare. Presiding judge Koji Iwata ruled that Unit 731, on the orders of the Imperial Japanese Army headquarters, used bacteriological weapons on Chinese civilians between 1940 and 1942, spreading diseases, including plague and typhoid, in the cities of Quzhou, Ningbo, and Changde. He rejected victims' compensation claims on the grounds that they had already been settled by international peace treaties.[132]

In October 2003, a member of Japan's House of Representatives filed an inquiry. Prime Minister Junichiro Koizumi responded that the Japanese government did not then possess any records related to Unit 731, but recognized the gravity of the matter and would publicize any records located in the future.[133] In April 2018, the National Archives of Japan released the names of 3,607 members of Unit 731, in response to a request by Professor Katsuo Nishiyama of the Shiga University of Medical Science.[134][135]

After World War II, the Office of Special Investigations created a watchlist of suspected Axis collaborators and persecutors who are banned from entering the United States. While they have added over 60,000 names to the watchlist, they have only been able to identify under 100 Japanese participants. In a 1998 correspondence letter between the DOJ and Rabbi Abraham Cooper, Eli Rosenbaum, director of OSI, stated that this was due to two factors:

1. While most documents captured by the US in Europe were microfilmed before being returned to their respective governments, the Department of Defense decided to not microfilm its vast collection of documents before returning them to the Japanese government.
2. The Japanese government has also failed to grant the OSI meaningful access to these and related records after the war, while European countries, on the other hand, have been largely cooperative,[136] the cumulative effect of which is that information pertaining to identifying these individuals is, in effect, impossible to recover.

• The Narrow Road to the Deep North, a Booker Prize-winning 2014 novel by Australian writer Richard Flanagan, refers extensively to the atrocities committed by a doctor who served in Unit 731.
• Forest Sea (Polish: Leśne morze) (1960), a novel by a Polish writer and educator Igor Newerly, was the first book published outside Asia which refers to atrocities committed in the unit.
• The Man Who Ended History: A Documentary (2011), a novella published in The Paper Menagerie book by American writer and Chinese translator Ken Liu: A scientific discovery allows a victim's descendant to go back in time to witness and learn the truth about the atrocities committed in the unit.
• Tricky Twenty-Two, a novel in the Stephanie Plum series by Janet Evanovich, features as its antagonist a deranged biology professor who is obsessed with Unit 731 and is attempting to recreate the unit's bubonic plague dispersals.
• The Solomon Curse, a novel in the Fargo Adventures series by Clive Cussler and Russell Blake, involves this unit in its plot, around secret human experimentation on the island of Guadalcanal.
• The Grimnoire Series, an alternative-history series of novels by Larry Correia, has Unit 731 conducting brutal magical experiments on prisoners of the Japanese Imperium.
• "Setting Sun" story from Hellblazer #142 by DC Comics, written by Warren Ellis and illustrated by Javier Pulido, features a fictitious character who used to be a doctor in Unit 731 during the war and conducted experiments on humans.
• In the manga My Hero Academia, a mad scientist who conducts experiments on humans to create a genetically modified race was first introduced as Shiga Maruta. Because of the association with the Maruta project, it caused a major controversy, especially in China, where Tencent and Bilibili removed the manga from their platforms.[137] Both Weekly Shonen Jump magazine and the author Kōhei Horikoshi issued individual apologizing statements on Twitter,[137] and the character name was changed in subsequent publications.[138]
• Crisis in the Ashes, by William W. Johnstone features the grandson of Dr. Ishi who has samples of the bubonic plague that he is trying to use to stop the liberal dictator of the US from using to conduct ethnic cleansing.
• Occupied City (2010), a novel by British author David Peace who lives in Japan, presents a mystery about a murder on 26 January 1948 in Tokyo. A murderer poisons bank employees by pretending to be a government official administering a dysentery vaccine. Gradually, through the testimonies of various people connected to the tragedy, it becomes clear that the poisoner has a shared history with Unit 731.
• The Collector – Unit 731, a four-issue miniseries by Dark Horse Comics, written by Rod Monteiro and co-written and illustrated by Will Conrad, features a fictitious character who is captured by the Kenpeitai in Tokyo and taken to the Unit 731 as a prisoner of war.
• The English Führer (2023) by Rory Clements involves the use of biological weapons developed by Unit 731.[139]

There have been several films about the atrocities of Unit 731.

• Through Gobi and Khingan (1981); Coproduction of USSR, Mongolia, Eastern Germany. Miniseries (two episodes).
• The Sea and Poison (1986), Japan, directed by Kei Kumai
• Men Behind the Sun (1988), China, directed by Tun Fei Mou
• Unit 731: Laboratory of the Devil (1992), China, directed by Godfrey Ho
• Kizu (les fantômes de l'unité 731) (2004), France, directed by Serge Viallet
• 731: Two Versions of Hell (2007), produced by James T. Hong; documentary about Unit 731 told from the Chinese and Japanese sides[140]
• Philosophy of a Knife (2008), Russia, directed by Andrey Iskanov
• Dead Mine (2012), Indonesia, directed by Steven Sheil and based in a fictionalized version of Unit 731
• Dongju: The Portrait of a Poet (2016), South Korea, directed by Lee Junik, depicts dead poet Yoon Dong-ju
• Wife of a Spy (2020), Japan, directed by Kiyoshi Kurosawa and won the Silver Lion for Best Direction at the Venice Film Festival in 2020.

• "The Breeding House" (1994), Bruce Dickinson. Segment of the CD-single Tears of the Dragon, describing the atrocities committed by Unit 731 and the immunity granted by the Americans to the physicians of the Unit
• "Unit 731" (2009), American thrash metal band Slayer. Song on the album World Painted Blood, describing the events and atrocities that occurred at Unit 731
• "Unit 731" (2011), Power electronic band Brandkommando
• "And You Will Beg for Our Secrets" (2016), from the Anaal Nathrakh album The Whole of the Law, refers to Unit 731's activities and the US amnesty given in exchange for information resulting from the experiments carried out.
• "The New Eternity" (2018), from the Silent Planet album When the End Began refers to Unit 731's human experimentation and other crimes against humanity.
• "Maruta" (2009), South Korean metal band Sad Legend.
• "Unit 731" (2021), single from German Deathstep producer Kroww.

• Unit 731 – Did the Emperor Know? (1985) Television South documentary first broadcast on 13 August.[141]
• The X-Files episode "731" (1995). Former members of Unit 731 secretly continue their experiments on humans under control of a covert US government agency.
• ReGenesis episode "Let it burn" (2007). Outbreaks of anthrax and glanders are traced to World War II Japan.
• Warehouse 13 episode "The 40th Floor" (2011). General Shirō Ishii's medal from Unit 731 simulated drowning when applied to a victim's skin.
• Concrete Revolutio. The experimentation on superhumans by the Japanese and Americans is a parallel to Unit 731.
• 731 (Chinese: 七三一) (2015). A five-episode CCTV documentary broadcast in 2015.
• The Truth of Unit 731: Elite medical students and human experiments (2017). An NHK Documentary broadcast in 2017, including paper materials, recording tapes, and interviews to former members and doctors who have implemented experiments in Unit 731.
• In The Blacklist, the episode "General Shiro" is a reference to Shirō Ishii.
• Link to part of a recorded telephone interview with Yoshimura Hisato.
• Kamen Rider Black Sun: A 10 episode (2022) Amazon Prime Video reboot of the original Kamen Rider Black in Japan. The Kaijin experiments is similar to Unit 731. Dounami Michinosuke began the experiments in 1936. The title "業部総務司長(Chief General Affairs Officer)" is written on the document. It was also in 1936 that Nobusuke Kishi got the title of "業部総務司長(Chief General Affairs Officer)" in Manchuria, China.

• In Call of Duty: Black Ops III, the Zombies map included in the second DLC pack, "Zetsubou no Shima", is loosely inspired by Unit 731's divisions, with the story playing on the idea of a ninth hidden one aptly named 'Division 9'.
• In the indie horror game Spooky's Jumpscare Mansion, the Unit 731 experiments are explicitly referenced multiple times in terms of Specimen 9 (specifically stated to be a survivor of the Unit 731 experiments), as well as the labeling of human bodies as "logs": "I'm taking all those 'logs' they keep throwing out, and I'm nailing them together."