Staff at a facility disguised as a lumber mill referred to their prisoners as maruta, or logs. This episode examines Unit 731, the Imperial Japanese Army's biological and chemical warfare program, drawing on trial records, documents, and testimony from former members. We trace how Shiro Ishii read the 1925 Geneva Protocol's ban as proof that biological weapons worked, how the 1931 occupation of Manchuria provided an unregulated site at Pingfang near Harbin, and how the operation was authorized by imperial decree under the name Epidemic Prevention and Water Purification Department.

The episode describes the six-square-kilometer complex and its 3,000 staff, the vivisections without anesthesia, forced infections, frostbite experiments, and the testimony of Nakagawa Yonezo that much of it amounted to playing around rather than science. It then  ...