Unit 731
Unit 731, officially known as the Manchu Detachment 731 and also referred to as the Kamo Detachment and the Ishii Unit, was a secret research facility operated by the Imperial Japanese Army between 1936 and 1945. It was located in the Pingfang district of Harbin, in the Japanese puppet state of Manchukuo, and maintained multiple branches across mainland China and Southeast Asia.
Unit 731 was responsible for large-scale biological and chemical warfare research, as well as lethal human experimentation. The facility was led by General Shirō Ishii and received strong support from the Japanese military. Its activities included infecting prisoners with deadly diseases, conducting vivisection, performing organ harvesting, testing hypobaric chambers, amputating limbs, and exposing victims to chemical agents and explosives. Prisoners—often referred to as "logs" by the staff—were mainly Chinese civilians, but also included Russians, Koreans, and others, including children and pregnant women. No documented survivors are known.
An estimated 14,000 people were killed inside the facility itself. In addition, biological weapons developed by Unit 731 caused the deaths of between 200,000 and 500,000 people in Chinese cities and villages, through deliberate contamination of water supplies, food, and agricultural land.
After the war, twelve Unit 731 members were tried by the Soviet Union in the 1949 Khabarovsk war crimes trials and sentenced to prison. However, many key figures, including Ishii, were granted immunity by the United States in exchange for their research data. The Truman administration concealed the unit's crimes and paid stipends to former personnel.
On 28 August 2002, the Tokyo District Court formally acknowledged that Japan had conducted biological warfare in China and held the state responsible for related deaths.
Formations
The Empire of Japan initiated its biological weapons program during the 1930s, due to the prohibition of biological weapons in interstate conflicts by the Geneva Protocol of 1925. They reasoned that the ban implied their efficacy as weapons. Japan's occupation of Manchuria began in 1931, after the Japanese invasion of Manchuria. Japan decided to build Unit 731 in Manchuria because the occupation not only gave the Japanese an advantage of separating the research station from their island but also gave them access to as many Chinese individuals as they wanted for use as test subjects. They viewed the Chinese as no-cost assets and hoped this ready supply of test subjects would give them a competitive advantage in biological warfare. Most of the victims were Chinese, but many victims were also of different nationalities. These facilities contained more than just medical research and experimentation areas; they also included spaces for detaining victims, essentially functioning as a prison. The research and experimentation rooms were constructed around the detention area, allowing researchers to conduct their daily work while monitoring the prisoners.Founded in 1936, Unit 731 expanded to include 3,000 staff members, 150 structures, and the capacity to detain up to 600 prisoners concurrently for experimental purposes.
Unit 731 was operated as a clandestine division of Japanese Kwantung Army, based in Manchuria during World War II. Led by Lieutenant General Shirō Ishii, the organization dedicated to the advancement of biological weaponry within the imperial army was commonly referred to as the Ishii Network. The Ishii Network was headquartered at the Epidemic Prevention Research Laboratory, established in 1932 at the Japanese Army Military Medical School in Tokyo. Unit 731 was the first among several covert units established as offshoots of the research lab, serving as field stations and experimental sites for advancing biological warfare techniques. These efforts culminated in the experimental deployment of biological weapons on Chinese cities, a direct breach of the 1925 Geneva Protocol prohibiting the use of biological and chemical weapons in warfare. Participants in these activities were aware of the violations and recognized the inhumanity of using human subjects in laboratory experiments, prompting the establishment of Unit 731 and other secret units.
Under the direction of Shirō Ishii, the Epidemic Prevention Research Laboratory was established following his return from a two-year exploration of American and European research institutions. With the endorsement of high-ranking military officials, it was established for the purpose of developing biological weapons. Ishii aimed to create biological weapons with humans as their intended victims, and Unit 731 was formed specifically to pursue this objective. Ishii organized a secret research group, the "Tōgō Unit", for chemical and biological experimentation in Manchuria.
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. It was divided at that time into the "Ishii Unit" and the "Wakamatsu Unit", with a base in Xinjing. From August 1940 on, the units were known collectively as the "Epidemic Prevention and Water Purification Department of the Kwantung Army" or "Unit 731" for short.
One of Ishii's main supporters inside the army was Colonel Chikahiko Koizumi, who later served as 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 Imperial Japanese Army officers were impressed by the successful German use of chlorine gas at the Second Battle of Ypres, in which the Allies suffered 6,000 deaths and 15,000 wounded as a result of the chemical attack.
Zhongma Fortress
Unit Tōgō was set into motion in the Zhongma Fortress, a prison and experimentation camp in Beiyinhe, a village south of Harbin on the South Manchuria Railway. The prisoners brought to Zhongma included common criminals, captured bandits, and anti-Japanese partisans, as well as political prisoners and people rounded up on false 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. A prison break in the autumn of 1934, which jeopardized the facility's secrecy, and an explosion in 1935, that was believed to be sabotage, led Ishii to shut down the Zhongma Fortress. He then received authorization to move to Pingfang, approximately south of Harbin, to set up a new, much larger facility.Other units
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, and a chemical warfare development unit called the Kwantung Army Technical Testing Department. 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, Malaya, Indonesia, the Philippines, Papua New Guinea, Thailand, and Burma. All of these units comprised Ishii's network, which, at its height in 1939, oversaw over 10,000 personnel. Medical doctors and professors from Japan were enticed to join Unit 731 both by the rare opportunity to conduct human experimentation and the Army's strong financial backing.Experiments
The military police and the Special Services Agency were responsible for finding victims to be test subjects for the unit, while a group of physicians were responsible for maintaining healthy victims and dispatching them for experimentations. Not all individuals sent to Unit 731 underwent experiments; these experiments were reserved for healthy individuals, and once accepted into the program, the preservation of their health became a top priority.Human experiments involved intentionally infecting captives, especially Chinese prisoners of war and civilians, with disease-causing agents and exposing them to bombs designed to disperse infectious substances upon contact with the skin. There are no records indicating any survivors from these experiments; those who did not die from infection were murdered for autopsy analysis. After human experimentations, researchers commonly used either potassium cyanide or chloroform to kill survivors.
According to American historian Sheldon H. Harris:
The Togo Unit employed gruesome tactics to secure specimens of select body organs. If Ishii or one of his co-workers wished to do research on the human brain, then they would order the guards to find them a useful sample. A prisoner would be taken from his cell. Guards would hold him while another guard would smash the victim's head open with an axe. His brain would be extracted off to the pathologist, and then to the crematorium for the usual disposal.
Nakagawa Yonezo, professor emeritus at Osaka University, studied at Kyoto University during the war. While he was there, he watched footage of human experiments and executions from Unit 731. He later testified about the playfulness of the experimenters:
Some of the experiments had nothing to do with advancing the capability of germ warfare, or of medicine. There is such a thing as professional curiosity: 'What would happen if we did such and such?' What medical purpose was served by performing and studying beheadings? None at all. That was just playing around. Professional people, too, like to play.
Prisoners were injected with diseases, 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. A special project, codenamed Maruta, used human beings for experiments. Test subjects were gathered from the surrounding population and sometimes euphemistically referred to as "logs", used in such contexts as "How many logs fell?" This term originated as a joke on the part of the staff because the official cover story for the facility given to local authorities was that it was a lumber mill. According to a junior uniformed civilian employee of the Imperial Japanese Army working in Unit 731, the project was internally called "Holzklotz", from the German word for log. The corpses of "sacrificed" subjects were disposed of by incineration. Researchers in Unit 731 also published some of their results in peer-reviewed journals, writing as though the research had been conducted on nonhuman primates called "Manchurian monkeys" or "long-tailed monkeys".
At the age of 14, on the encouragement of a former school teacher, Hideo Shimizu joined the fourth group of minors assigned to Unit 731. He recalled that he was brought to a specimen room where jars of various heights, with some reaching the height of an adult, were stored. The jars held body parts from humans preserved in formalin, such as heads and hands. There was also a pregnant woman's body with a large belly, where the lower part was exposed to reveal a fetus with hair. Shimizu discovered that the term "logs" was used dehumanizingly to refer to prisoners. He also learned that the prisoners were further dehumanized by being held in facilities referred to as "log cabins".