From 1938-1945 Ishii carried on experiments against POW's, including US forces at the Mukden POW Camp in northeast China. He directed Unit 731, the secret Japanese unit engaged in human experimentation. Ishii was initially given command of the "Togo Unit" of 300 men, which rapidly grew and acquired additional "cover" identities. The first major BW facility was built at Beiyinhe, some 70km outside Harbin, known locally as the "Zhong Ma Prison Camp. Open air testing on prisoners was conducted at the the officially named "Water Purification Unit 731" at Pingfan near Harbin, a remote, desolate area on the Manchurian Peninsula. Pingfan's 6 square kilometers housed more than 150 buildings, including administrative buildings, laboratories, workers dormitories, and barracks. By 1945, the Japanese program had stockpiled 400 kilograms of anthrax to be used in a specially designed fragmentation bomb. Studies continued there until 1945, when the Unit 731 complex was leveled by burning it.
Slightly less than 1,000 human autopsies apparently were carried out at Unit 731, most on victims exposed to aerosolized anthrax. Many more prisoners and Chinese nationals may have died in this facility - some have estimated up to 3,000 human deaths. In 1940, a plague epidemic in China and Manchuria followed reported overflights by Japanese planes dropping plague-infected fleas. The Japanese attacked hundreds of heavily populated communities and remote regions with germ bombs. There appears to have been a massive germ war campaign in Yunnan Province bordering Burma. Planes dropped plague-infected fleas over Ningbo in eastern China and over Changde in north-central China, Japanese troops also dropped cholera and typhoid cultures in wells and ponds. In all, tens of thousands, and perhaps as many 200,000, Chinese died of bubonic plague, cholera, anthrax and other diseases.
In August 1955, Hiroshi Akiyama's "Saikin Sen wa Jumbi Sareteita!" (Bacteriological Warfare Preparations Were Already Complete!) described in revolting detail his alleged experiences with the infamous Unit 731. His ostensible purpose: "To help in some small measure to warn people against the horrors of a third World War, and to prevent such horrors from occurring." The Akiyama piece stirred up violent controversy.The US Veteran's Administration Secretary's Advisory Committee on former Prisoners of War was formed to locate any survivors who were POWs at the Japanese Mukden Prison Complex during WW 11. The committee attempted to verify information that some POWs at Mukden's Unit 731 may have been the victims of medical experiments.
The Chinese government has erected a museum on the former grounds of a Japanese biowarfare testing center that used Chinese as subjects during WWII.
In 1972, Japan and many other countries signed the Convention on the Prohibition of the Development, Production and Stockpiling of Bacteriological (Biological) and Toxin Weapons and on Their Destruction, commonly called the Biological Weapons Convention. This treaty prohibits the stockpiling of biological agents for offensive military purposes, and also forbids research into such offensive employment of biological agents.