Unit 731 Biological Warfare Experiments (1937-1945)

Japan's Unit 731 in Manchuria conducted biological and chemical warfare experiments on thousands of Chinese, Korean, and Allied prisoners — including vivisection without anaesthesia, deliberate infection with plague and cholera, and frostbite testing. An estimated 3,000 to 12,000 people were killed. In a controversial Cold War deal, the US granted immunity to Unit 731 researchers in exchange for their data, and Japan has never formally acknowledged the programme's full scope.