Unit 731 , short for Manchu Detachment 731 and also known as the Kamo Detachment and the 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. It killed an estimated 200,000 to 300,000 people. It was based in the Pingfang district of Harbin, the largest city in the Japanese puppet state of Manchukuo and had active branch offices throughout China and Southeast Asia.

The Kempeitai was the military police of the Imperial Japanese Army. The organization also shared civilian secret police, espionage, and counter-intelligence roles within Japan and its occupied territories, and was notorious for its brutality and role in suppressing dissent. The broad duties of the Kempeitai included maintaining military discipline, enforcing conscription laws, protecting vital military zones, and investigating crimes among soldiers. In occupied areas, it also issued travel permits, recruited labor, arrested resistance, requisitioned food and supplies, spread propaganda, and suppressed anti-Japanese sentiment. At its peak at the end of World War II, the Kempeitai was an extensive corps with about 35,000 personnel.