Flown by 393d commander, Major Charles W. Sweeney, it was assigned to the Hiroshima mission on 6 August 1945, as the blast measurement instrumentation aircraft.[1] On the mission to bomb Nagasaki on 9 August 1945, it was to have been the aircraft carrying the bomb, but the mission schedule had been moved forward two days because of weather considerations, and the instrumentation had not yet been removed from the aircraft. To avoid delaying the mission, Sweeney traded airplanes with the crew of Bockscar to carry the Fat Man atomic bomb to Nagasaki.