Unit 731 and Japan's germ warfare program

Unit 731 was a secret research unit of the Imperial Japanese Army, officially called the Epidemic Prevention and Water Purification Department of the Kwantung Army. From 1936 it operated a walled compound at Pingfang, near Harbin in occupied Manchuria, under the army doctor Shiro Ishii. Inside, scientists bred plague-carrying fleas, grew anthrax, cholera and typhoid in bulk, and tested them on prisoners, mostly Chinese, along with Russians, Koreans and others. Staff referred to the prisoners as maruta, meaning logs. Prisoners were deliberately infected, exposed to freezing to study frostbite, and dissected, sometimes while still alive.¹

The unit grew out of Japan's seizure of Manchuria in 1931, which created a colony run by the army where secret work could hide in plain sight. Ishii argued that Japan, short of raw materials, needed cheap weapons, and germ theory made disease something a laboratory could produce on demand. The 1925 Geneva Protocol banned using such weapons but not researching them, and Ishii read the ban as proof that rival powers feared them.¹²

The unit and its sister units also took the weapons into the field. Aircraft dropped plague-infected fleas on Chinese cities such as Ningbo in 1940 and Changde in 1941, and cholera and other agents were spread during campaigns in 1942. Thousands of prisoners died inside the compound, and estimates of the deaths caused by the field attacks run into the tens of thousands, though the exact toll is disputed. In August 1945 the staff blew up the buildings and killed the remaining prisoners. The Soviet Union tried twelve captured members at Khabarovsk in 1949, but Ishii and his senior colleagues were never prosecuted, because American officials granted them immunity in exchange for their experimental data. Many went on to prominent careers in Japanese medicine and industry.¹²⁴⁵