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 the code name of an Imperial Japanese Army unit officially known as the Kempeitai Political Department and Epidemic Prevention Research Laboratory. It was initially set up under the Kempeitai military police of the Empire of Japan to develop weapons of mass destruction for potential use against Chinese, and possibly Soviet forces.
Unit 731 was based at the Pingfang district of Harbin, the largest city in the Japanese puppet state of Manchukuo (now Northeast China). More than ten thousand people, from which around 600 every year were provided by the Kempeitai, were subjects of the experimentation conducted by Unit 731.
More than 95 percent of the victims who died in the camp based in Pingfang were Chinese and Korean, including both civilian and military. The remaining 5 percent 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.
According to the 2002 International Symposium on the Crimes of Bacteriological Warfare, the number of people killed by the Imperial Japanese Army germ warfare and human experiments is around 580,000. According to other sources, the use of biological weapons researched in Unit 731's bioweapons and chemical weapons programs resulted in possibly as many as 200,000 deaths of military personnel and civilians in China.
Unit 731 was the headquarters of many subsidiary units used by the Japanese to research biological warfare; other units included Unit 516 (Qiqihar), Unit 543 (Hailar), Unit 773 (Songo unit), Unit 100 (Changchun), Unit Ei 1644 (Nanjing), Unit 1855 (Beijing), Unit 8604 (Guangzhou), Unit 200 (Manchuria) and Unit 9420 (Singapore).
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.
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.
Because of their brutality, Unit 731's actions have since been declared by the United Nations to have been crimes against humanity.
In 1932, General Shiro Ishii (ç