, short for Manshu Detachment 731 and also known as Kamo Detachment, Ishii Unit, 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) of World War II. It was responsible for some of the most notorious war crimes carried out by Imperial Japan. Unit 731 was based at 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.