Zhongma Fortress — also Zhong Ma Prison Camp or Unit Tōgō — was a prison camp where the Japanese Kwantung Army carried out covert biological warfare research on human test subjects . Built in Beiyinhe , outside of Harbin , Manchukuo during the Second Sino-Japanese War , the camp served as a center for human subject experimentation and could hold up to 1,000 prisoners at any given time . In 1937 the prison camp was destroyed and testing operations were transferred to Pingfang under Unit 731
Unit 731
Unit 731
Zhongma Fortress