May 15, 2020 In 1936, the Japanese built Unit 731 — the administrative center of the top-secret biological warfare project of the Imperial Japanese Army — in the isolated Pingfang District of the city of Harbin in Manchuria. At the time, Harbin was a city with a large Russian minority population, and writer Morimura Seiichi has hypothesized that of the 3,000 prisoners experimented on at Unit 731, up to 30% were Russian.