After the Japanese invaded Manchuria in 1931-1932, the young Ishii headed the scientific research conducted in the Zhong Ma fortress, a prison camp and Japan's first testing facility looking into the development of biological weapons. The project was sponsored by the Japanese Emperor himself. Under Ishii's leadership, the Japanese conducted horrendous experiments on the Chinese peasants in Manchuria, taking blood samples, dissecting prisoners and infecting them with bubonic plague, in order to find out more about the human body and how to weaponise germs. During the Pacific War, Japan dropped germ-ridden packages on Chinese towns and villages, killing hundreds of thousands of people. Meanwhile, the research was continued in Zhong Ma's successor, Unit 731.
After Japan surrendered at the end of World War II in 1945, the Americans offered Ishii and the other perpetrators immunity from their crimes if they handed over the data gathered from the experiments in Zhong Ma and Unit 731. Ishii was never punished for his crimes and lived out the remainder of his life in comfort. The Americans even incorporated his research into their own medical knowledge, and used biological weapons against North Korea in the Korean War. (PROSE: Log 384)