Coming to light gradually:
“That research program was one of the great secrets of Japan during and after World War II: a vast project to develop weapons of biological warfare, including plague, anthrax, cholera and a dozen other pathogens.
Experiments on Chinese civilians:
unit 731 of the Japanese Imperial Army conducted research by experimenting on humans and by “field testing” plague bombs by dropping them on Chinese cities to see whether they could start plague outbreaks. They could.
Two Chinese men were brought in, stripped naked and given general anesthetic. Then Dr. Yuasa and the others began practicing various kinds of surgery: first an appendectomy, then an amputation of an arm and finally a tracheotomy. After 90 minutes, they were finished, so they killed the patient with an injection.
The research was kept secret after the end of World War II in part because the U.S. Army granted immunity from war crimes prosecution to the doctors in exchange for their research data. Japanese and U.S. documents show that the United States helped cover up the human experimentation and instead of putting the ringleaders on trial, it gave them stipends.