On 21 March 1946, Strategic Air Command (SAC) was activated and on 31 March 1946, SAC's Fifteenth Air Force assumed operation of Kirtland Field. The 58th Bombardment Wing remained in command of the installation under SAC, and there was a return of personnel. Shortly thereafter, an "S-2 Section" was established on base and became responsible for the security of Kirtland Field and the "W-47 Project". The W-47 Project had been the wartime operation established at Wendover Army Air Base to train the 509th Composite Group to drop the atomic bombs on Hiroshima and Nagasaki. In keeping with Kirtland Field's mission to assist Sandia Base's Z Division with the marriage of bombs and aircraft, the 509th Composite Group's Flight Test Section was transferred to Kirtland.