from numerous cigarettes. His officer's sword was poorly fastened and dragged on the floor". However, in Manchuria, Ishii would transform into a different character: "he was dressed immaculately. His uniform was spotless, and his sword was tied correctly". Further promotions for Ishii would follow; he was promoted to Senior Army Surgeon, First Class (surgeon colonel) in 1938, Assistant Surgeon General (surgeon Major General) in March 1941, and Surgeon General (surgeon Lieutenant General) in March 1945. Towards the end of the war Ishii would develop a plan to spread plague fleas along the populated west coast of the US, known as Operation Cherry Blossoms at Night. This plan was not realized due to the surrender of Japan on August 15, 1945. Ishii and the Japanese government attempted to cover up the facilities and experiments, but ultimately failed with their secret university lab in Tokyo and their main lab in Harbin, China. The Japanese Army's Unit 731 War Crimes Exhibition Hall (731罪证陈列馆)[ex] in Harbin stands to this day as a museum to the unit and the atrocities they committed. War crime immunity Ishii was arrested by United States authorities during the Occupation of Japan at the end of World War II and, along with other leaders, was supposed to be thoroughly interrogated by Soviet authorities. Instead, Ishii and his team managed to negotiate and receive immunity in 1946 from Japanese war-crimes prosecution before the Tokyo tribunal in exchange for their full disclosure. Although the Soviet authorities wished the prosecutions to take place, the United States objected after the reports of the investigating US microbiologists. Among these was Edwin Hill, the Chief of Fort Detrick, whose report stated that the information was "absolutely invaluable;" it "could never have been obtained in the United States because of scruples attached to experiments on humans" and "the information was obtained fairly cheaply." On May 6, 1947, Douglas MacArthur wrote to Washington, D.C., that "additional data, possibly some statements from Ishii probably can be obtained by informing Japanese involved that information will be retained in intelligence channels and will not be employed as 'War Crimes' evidence." Ishii's immunity deal was concluded in 1948 and he was never prosecuted for any war crimes, and his exact whereabouts or occupation were unknown from 1947. Richard Drayton, a Cambridge University history lecturer, claimed that Ishii later went to Maryland to advise on bioweapons. Another source says he stayed in Japan,