Short answers, pulled from the story.
The Empire of Japan established Unit 731 in 1936 within the Pingfang district of Harbin, Manchukuo. The facility operated until 1945 while maintaining multiple branches across mainland China and Southeast Asia.
Lieutenant General Shirō Ishii commanded Unit 731 from its inception in 1936. By 1939 the organization had expanded to include over 3,000 staff members and 150 structures.
Shirō Ishii condensed laboratory discoveries into six potent pathogens including anthrax, typhoid, paratyphoid, glanders, dysentery, and plague-infected fleas by 1939. Low-flying aircraft spread plague-infected fleas over Chinese cities including coastal Ningbo and Changde in 1940 and 1941.
General Douglas MacArthur struck a deal granting immunity to physicians including their leader Shirō Ishii in September 1945. This agreement provided exclusive American access to research data from human experimentation in exchange for secrecy.
Tokyo District Court formally acknowledged that Japan conducted biological warfare in China in August 2002. Presiding judge Koji Iwata ruled Unit 731 used bacteriological weapons on Chinese civilians between 1940 and 1942.