Zhongma Fortress

Zhongma Fortress (Chinese: 中馬城) — 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.