Until the end of World War II , Japan operated a covert biological and chemical warfare research and development unit called Unit 731 in Harbin . The unit 's activities , including human experimentation , were documented by the Khabarovsk War Crime Trials conducted by the Soviet Union in December 1949 . However , at that time , the US government described the Khabarovsk trials as " vicious and unfounded propaganda " . It was later revealed that the accusations made against the Japanese military were correct . The US government had taken over the research at the end of the war and had then covered up the program . Leaders of Unit 731 were exempted from war crimes prosecution by the United States and then placed on the payroll of the US . On 30 June 1950 , soon after the outbreak of the Korean War , the US Defense Secretary George Marshall received the '' Report of the Committee on Chemical , Biological and Radiological Warfare and Recommendations '' , which advocated urgent development of a biological weapons program . The biological weapons research facility at Fort Detrick in Maryland was expanded , and a new one in Pine Bluff , Arkansas was developed
Unit 731
Unit 731
Allegations of biological warfare in the Korean War