Unit 731 (731 部隊, Nana-san-ichi butai) 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. Officially known by the Imperial Japanese Army 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.