In 1932, he began his preliminary experiments in biological warfare as a secret project for the Japanese military. In 1936, Unit 731 was formed. Ishii built a huge compound – more than 150 buildings over six square kilometers – outside the city of Harbin, China. The research was secret, and the cover story was that Unit 731 was engaged in water-purification work. The film Men Behind the Sun (Hong Kong, 1988, directed by Mou Tun Fei) includes a scene in which Ishii demonstrates to his fellow soldiers a machine he has invented to purify urine into drinking water.
From 1940, Ishii was appointed Chief of the Biological Warfare Section of the Kwantung Army, holding the post simultaneously with that of the Bacteriological Department of the Army Medical Academy.[1]
In 1942, Ishii began field tests of germ warfare agents developed, and various methods of dispersion (i.e. via firearms, bombs etc.) both on Chinese prisoners of war and operationally on battlefields and against civilians in Chinese cities. Some historians[citation needed] estimate that tens of thousands died as a result of the bio-weapons (including bubonic plague, cholera, anthrax and others) deployed. His unit also conducted physiological experiments on human subjects, including vivisections, forced abortions, and simulated strokes and heart attacks.
From 1942-1945, Ishii was Chief of the Medical Section of the Japanese First Army[1]
In 1945, in the final days of the Pacific War and in the face of imminent defeat, Japanese troops blew up the headquarters of Unit 731 in order to destroy evidence of the research done there. As part of the cover-up, Ishii ordered 150 remaining subjects killed. More than ten thousand people,[2] from which around 600 every year were provided by the kempeitai,[3] were subjects of the experimentation conducted by Unit 731. These were called by Ishii and his peers maruta "logs," a reference to their view of subjects being inert, expendable entities, or is possibly related to the cover story told to locals that the facility contained a sawmill.