Unit 731 Biological Warfare Experiments (1937-1945)

Unit 731's biological warfare experiments on prisoners in Manchuria remain the deadliest unpunished war crime in science. Perpetrators conducted vivisection without anesthesia and deliberately infected victims with plague and cholera, killing an estimated 3,000 to 12,000 people—a toll that exceeds the combined death count of MKUltra and the Monster Study by a factor of 30. The U.S. granted immunity to researchers in exchange for their data, a Cold War deal that ensured Japan never formally acknowledged the program's full scope.