Ishii led the development and application of biological weapons at Unit 731 in Manchukuo during the Second Sino-Japanese War from 1937 to 1945, including the bubonic plague attacks at Chinese cities of Changde and Ningbo, and planned the Operation Cherry Blossoms at Night biological attack against the United States. Ishii and his colleagues also engaged in human experimentation, resulting in the death of over 10,000 people, most of them civilians or prisoners of war. They were later granted immunity in the International Military Tribunal for the Far East by the United States government in exchange for information and research for the U.S. biological warfare program.