Unit 731

Unit 731 was a secret research unit run by the Imperial Japanese Army from 1933 to 1945. It worked on biological and chemical weapons. Its official name was Manchu Detachment 731, and it was also called the Kamo Detachment and the Ishii Unit.

The main site was in the Pingfang district of Harbin, in the Japanese-controlled state of Manchukuo. That area is now part of Northeast China. From there, the unit ran several branches across mainland China and Southeast Asia. During the Second Sino-Japanese War, the unit carried out biological weapons attacks that poisoned water, food, and crops. These attacks harmed and killed a very large number of people in towns and villages.

The unit was led by General Shirō Ishii and had strong support from the Japanese military. Many people died from human experimentation at the facility. The prisoners, whom staff called "logs" (or "maruta"), were mostly Chinese civilians. Others were Russians, Koreans, and people from other places, including children. The prisoners were treated very badly. They were used in cruel experiments, including tests in special chambers and exposure to dangerous chemicals and explosives. Sadly, no survivors are known.

After the war, twelve Unit 731 members were tried by the USSR in the 1949 Khabarovsk war crimes trials. They received fairly light prison sentences. Ishii and other members were not put on trial by the United States, which wanted their research. American officials also worried that a trial would reveal this information to the USSR and show the U.S. had its own biological weapons work. The Americans granted them immunity in exchange for their research data. Later, that data was found to be of little value, because the American program was already more advanced than Japan's. The Truman administration kept the unit's crimes hidden and paid money to former members.

On 28 August 2002, the Tokyo District Court confirmed that Japan had carried out biological warfare in China and said the state was responsible for related deaths. However, the court did not award compensation. It said that postwar agreements, such as the Treaty of San Francisco, had already covered this. In April 2018, the National Archives of Japan released a nearly complete list of 3,607 people connected to Unit 731. The Japanese government has never officially admitted to its biological warfare.

Formations

The Empire of Japan began a program to develop biological weapons in the 1930s. The Geneva Protocol of 1925 banned these weapons in fights between countries, but Japan's leaders believed the weapons could still be useful. After the Japanese invasion of Manchuria began in 1931, Japan built Unit 731 there. Manchuria kept the research station away from Japan's islands. It also gave Japan access to many people from China. Many people were harmed, most of them Chinese, but others came from other countries too. The facilities included a prison area, and the research rooms were built around it. Founded in 1933, the unit grew to thousands of staff members and many buildings. It could hold hundreds of prisoners at once. Unit 731 was a secret part of the Kwantung Army in Manchuria. It was led by Lieutenant General Shirō Ishii, and its network was based at a laboratory in Tokyo, set up in 1932. In 1936, Emperor Hirohito approved the unit's expansion into the Kwantung Army, with a base in Xinjing. One of Ishii's main supporters was Colonel Chikahiko Koizumi, who later served as Japan's Health Minister from 1941 to 1945.

Main article: Epidemic Prevention and Water Purification Department

Unit 731 first worked at the Zhongma Fortress, a prison and research camp in Beiyinhe, about 100 kilometers (62 mi) south of Harbin, along the South Manchuria Railway. Its prisoners included criminals, captured bandits, anti-Japanese fighters, political prisoners, and people falsely accused by the Kempeitai. At first, prisoners were given good food, including rice or wheat, meat, fish, and sometimes alcohol. Some prisoners were infected with plague and other microbes during research. A prison break in 1934 and an explosion in 1935 led Ishii to close the fortress. He moved the work to Pingfang, near Harbin, where a much larger facility was built. A decree in 1936 also created the Kwantung Army Military Horse Epidemic Prevention Workshop, later called Unit 100, and the Kwantung Army Technical Testing Department, later called Unit 516. After the Japanese invasion of China in 1937, sister units were set up in major Chinese cities. These included Unit 1855 in Beijing, Unit Ei 1644 in Nanjing, and Unit 8604 in Guangzhou. Later units were added in Singapore, Malaya (now Malaysia), Indonesia, the Philippines, Papua New Guinea, Thailand, and Burma, including Unit 9420 in Singapore. At its largest in 1939, Ishii's network had more than 10,000 workers. Doctors and professors from Japan joined the unit, drawn by the research opportunities and by the Army's strong financial support.

Experiments

Unit 731 carried out many experiments on prisoners, most of them Chinese prisoners of war and civilians. Military police and a special agency found people to use. A group of doctors looked after them until they were taken for experiments. Many were deliberately infected with diseases. The unit also tested biological weapons and chemical weapons on prisoners. It studied the effects of extreme cold, heat, and hunger. Many prisoners died during the experiments. Biological attacks on Chinese cities spread bubonic plague and other diseases, including in Changde and Nanjing. Many people were harmed by these attacks.

The prisoners were treated as objects, not as people. A former member of the unit later said that some experiments had no medical purpose at all. Unit 731 is remembered as one of the cruelest programs of the war. Its story shows how important it is to treat all people with respect.

Prisoners and victims

After Japan lost World War II, the Japanese killed every prisoner in the unit. At the Pingfang camp alone, many men, women, and children were harmed in experiments. Many more were harmed at other sites, such as Unit 100. Most of the victims were Chinese, and there were also Russian, Mongolian, and Korean people. The people who were held included criminals, captured bandits, anti-Japanese partisans, political prisoners, homeless people, and mentally disabled people. Even children and pregnant women were among them. No Unit 731 prisoners survived, and the few who tried to escape did not succeed.

In 2002, a symposium in Changde, China, looked at the harm caused by the Imperial Japanese Army through germ warfare and other experiments on people. The American historian Sheldon H. Harris has also written about the many people who died.

Personnel and postwar accountability

Unit 731 had hundreds of military and civilian workers. They took part in harmful experiments on people during the war. They also worked on biological weapons and chemical weapons. After Japan surrendered, several members were held at the Fushun War Criminals Management Centre and the Taiyuan War Criminals Management Centre. Many were later sent back to Japan. Some joined the Association of Returnees from China and talked about what they had done.

Important members included Lieutenant General Shirō Ishii, who was the overall commander. Major General Masaji Kitano led the unit from 1942 to 1945. Lieutenant Colonel Ryōichi Naitō later founded Green Cross. Others included Prince Tsuneyoshi Takeda, Prince Naruhiko Higashikuni, Yoshio Shinozuka, who later gave testimony, Yasuji Kaneko, who also later gave testimony, Shigeru Fujita, and Ken Yuasa. Some civilian workers and students were Shigeo Ozeki, Kioyashi Mineoi, Masateru Saitō, and Yoshio Furuichi.

In 1949, the Soviet Union put twelve former members of Unit 731 and related units on trial in the Khabarovsk war crimes trials. The table below shows their ranks, jobs, and sentences.

In April 2018, the National Archives of Japan shared an almost complete list of more than 3,600 people linked to Unit 731. The list was given to Katsuo Nishiyama, a professor at Shiga University of Medical Science. Nishiyama said he planned to put the list online so that more people could study the unit. In August 2023, Seiya Matsuno of Meiji Gakuin University found a more detailed list of staff in the National Archives.

Divisions

Unit 731 was split into eight divisions:

• Division 1 studied bubonic plague, cholera, anthrax, typhoid, and tuberculosis. It used people as test subjects. A prison was built to hold many people for this purpose.
• Division 2 studied germs and parasites that could be used as weapons in the field.
• Division 3 made shells that held germs. It was based in Harbin.
• Division 4 grew and stored large amounts of bacteria.
• Division 5 trained staff.
• Divisions 6–8 handled equipment, medical work, and administration.

Facilities

Main article: Epidemic Prevention and Water Purification Department

Unit 731 had other units under it in its chain of command. Several other units were part of Japan's biological weapons programs. Most of these units had branch offices, which were also often called "Units." The name Unit 731 could refer to the Harbin complex or to the whole organization and its branches.

The Harbin complex covered about six square kilometers (2.3 square miles). It had more than 150 buildings, which were built to be hard to destroy by bombing. The complex had around 4,500 containers for raising fleas, six cauldrons for making chemicals, and about 1,800 containers for making biological agents. In a few days, about 30 kilograms (66 pounds) of bubonic plague bacteria could be produced. Some of its branch facilities are still used by Chinese industrial companies. Part of the site has been kept as a museum that visitors can see.

Unit 731 had branches in Linkou (Branch 162), Mudanjiang, Hailin (Branch 643), Sunwu (Branch 673) and Hailar (Branch 543). During World War II, a medical school and research facility that belonged to Unit 731 operated in the Shinjuku District of Tokyo.

In 2006, Toyo Ishii, a nurse who had worked at the school during the war, shared that soon after Japan's surrender in 1945, she helped bury remains on the school grounds. In response, the Ministry of Health began digging at the site in February 2011.

In 2002, Tokyo courts recognized that Unit 731 had been involved in biological warfare research. However, as of 2011, the Japanese government had not officially acknowledged the harm done to people. It also turned down Chinese government requests for DNA samples that could help identify remains found near an army medical school.

Surrender and immunity

As World War II came to an end, the prisoners at the compound were killed to hide the evidence, and no survivors were recorded. When the Red Army arrived in August 1945, the unit had to leave in a hurry. Officials in Tokyo ordered that all incriminating materials be destroyed, including those at Pingfang. Some Japanese troops blew up the compound in the last days of the war, but many parts were still somewhat intact. After Japan surrendered in 1945, Lieutenant Colonel Murray Sanders, a well-respected microbiologist, arrived to look into Japanese biological warfare. Little information was shared until he threatened to bring in the Soviets, because the Japanese wanted to avoid being tried under the Soviet legal system. Sanders took the information to General Douglas MacArthur, the Supreme Commander of the Allied Powers, who secretly granted immunity to the unit's doctors, including its leader Shirō Ishii. In return, American researchers gained access to their research.

The Tokyo War Crimes Tribunal heard only one brief mention of the experiments, and William Webb dismissed it for lack of evidence. While German physicians were brought to trial, the United States kept Japan's information hidden. In 1948 an American court in Yokohama tried Japanese doctors for experiments on captured American pilots, and two were sentenced to death. The Soviet Union put 12 top military leaders and scientists on trial. They came from Unit 731, Unit 1644 in Nanjing, and Unit 100 in Changchun, in the Khabarovsk war crimes trials. The lead prosecutor, Lev Smirnov, had also worked at the Nuremberg Trials. The defendants received sentences of 2 to 25 years in a Siberian labor camp, and all of them returned to Japan by 1956. The United States refused to recognize these trials. On 6 May 1947, MacArthur, the Supreme Commander of the Allied Forces, wrote to Washington. He said more information could be gained if Japanese participants were told it would be kept in intelligence channels and not used as war crimes evidence.

In popular culture

Unit 731 has appeared in many books and comics. Crisis in the Ashes (1999), a novel by William W. Johnstone, is about the grandson of a Unit 731 scientist who uses a deadly disease in a dangerous plan. The Man Who Ended History: A Documentary (2011), a novella by Ken Liu, tells of an inventor of time travel who uses the invention to show people the terrible things Unit 731 did. In My Hero Academia (2014–2024), a manga by Kōhei Horikoshi, a character originally named "Shiga Maruta" caused backlash for its link to Unit 731, and the name was later changed. The Solomon Curse (2015), a novel by Clive Cussler and Russell Blake, includes a side story about secret experiments linked to Unit 731. Tricky Twenty-Two (2015), a novel by Janet Evanovich, features a villainous biology professor who wants to copy Unit 731's ways of spreading disease. The Collector – Unit 731 (2021), a comic miniseries by Dark Horse Comics, written by Rod Monteiro and illustrated by Will Conrad, follows a prisoner of war who was captured and treated very badly by Unit 731.

Unit 731 has also been shown on television. Unit 731 – Did the Emperor Know? (1985), a documentary by Television South, looks into what Imperial Japan knew about Unit 731. 731 (Chinese: 七三一) (2015), a five-part CCTV documentary, shows the wrongs Unit 731 did and how it was remembered after the war. The Truth of Unit 731: Elite Medical Students and Human Experiments (2017), an NHK documentary, includes interviews and recovered records from people who worked in Unit 731. Gyeongseong Creature (2023–2024), a South Korean historical horror series, was inspired by Unit 731 and the harm it caused during Japanese occupation. 731 (2025), a Chinese movie, follows prisoners' experiences in Unit 731 in occupied Northeastern China.