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 Epidemic Prevention and Water Purification Department of the Kwantung Army. 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.