The Americans coopted the researchers' bioweapons information and experience for use in their own biological warfare program, much as they had done with German researchers in Operation Paperclip. The United States covered up the human experimentations and handed stipends to the perpetrators on trial. While Unit 731 researchers arrested by Soviet forces were tried at the December 1949 Khabarovsk war crime trials, those captured by the United States were secretly given immunity in exchange for the data gathered during their human experiments. Unit 731 and the other units of the Epidemic Prevention and Water Purification Department operated biological weapon production, testing, deployment, and storage facilities. The program received generous support from the Japanese government until the end of the war in 1945. The facility itself was built in 1935 as a replacement for the Zhongma Fortress, and Ishii and his team used it to expand their capabilities. Originally set up by the Kenpeitai military police of the Empire of Japan, Unit 731 was taken over and commanded until the end of the war by General Shirō Ishii, a combat medic officer in the Kwantung Army. It was officially known as the Epidemic Prevention and Water Purification Department of the Kwantung Army ( 関東軍防疫給水部本部, Kantōgun Bōeki Kyūsuibu Honbu).

Estimates of those killed by Unit 731 and its related programs range up to half a million people. Additionally, Unit 731 produced biological weapons that were used in areas of China not occupied by Japanese forces, which included Chinese cities and towns, water sources, and fields. Victims were from different nationalities, but the majority of them were Chinese. Victims included babies, children, and pregnant mothers. Experiments included disease injections, controlled dehydration, hypobaric chamber experiments, biological weapons testing, vivisection, amputation, and weapons testing.

Unit 731 routinely conducted tests on human beings who were dehumanized and internally referred to as 'logs'. It was responsible for some of the most notorious war crimes committed by the Japanese armed forces. Unit 731 was based in the Pingfang district of Harbin, the largest city in the Japanese puppet state of Manchukuo (now Northeast China), and had active branch offices throughout China and Southeast Asia. Unit 731 ( Japanese: 731部隊, Hepburn: Nana-san-ichi Butai), short for Manshu Detachment 731 and also known as the Kamo Detachment : 198 and Ishii Unit, was a covert biological and chemical warfare research and development unit of the Imperial Japanese Army that engaged in lethal human experimentation and biological weapons manufacturing during the Second Sino-Japanese War (1937–1945) and World War II.

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