Unit 731 , officially known as the Manchu Detachment 731 and also referred to as the Kamo Detachment and the Ishii Unit, was a clandestine biological and chemical warfare research facility, operated by the Imperial Japanese Army between 1933 and 1945. It was located in the Pingfang district of Harbin, in the Japanese puppet state of Manchukuo, and maintained multiple branches across mainland China and Southeast Asia under "Epidemic Prevention Department" umbrella. During the Second Sino-Japanese War, the unit led the largest attacks in the history of biological warfare, killing approximately 200,000 people in cities and villages, through deliberate contamination of water supplies, food, and agricultural land.