6.1 EARLY RADIATION SURVEYS. In the months immediately following the detonations, U.S. scientists conducted a number of onsite surveys to be sure that any residual radiation in Hiroshima and Nagasaki would not present a health hazard to occupation troops or to the Japanese remaining in the cities. General Marshall, U.S. Army Chief of Staff in Washington, addressed the first concern in a message sent to General MacArthur, the Theater Commander. General Marshall emphasized the importance of early radiation surveys so that the occupation troops "shall not be subjected to any possible toxic effects, although we have no reason to believe that any such effects actually exist." Three series of early radiation surveys followed: e Scientists from the Manhattan Engineer District, the organization that had developed the bombs, made rapid radiation surveys of Hiroshima on 8-9 September 1945 (1 month before occupation troops arrived in that area) and of Nagasaki on 13-14 September (10 days before the occupation troops arrived). -e The Manhattan Project Atomic Bomb Investigating Group made more extensive surveys in Nagasaki from 20 September to 6 October and in Hiroshima from 3 to 7 October 1945. -- e They reported negligible levels of radioactivity in the areas surveyed. Their measurements, detailed in extensive reports, showed the levels of residual radioactivity to be extremely low. The Naval Technical Mission to Japan surveyed Nagasaki during 15 to 27 October and Hiroshima on 1 to 2 November 1945. -- Their well-documented findings of negligible levels of radioactivity corroborated the earlier measurements. In addition to these surveys, the U.S. investigation teams used data from numerous separate radiation monitoring surveys, soil and debris sampling programs, and other analyses conducted by Japanese scientists in the days and weeks immediately following the bombings. 154