The Air Service was the first form of the air force to have an independent organizational structure and identity. Although officers concurrently held rank in various branches, after May 1918 their branch designation in official correspondence while on aviation assignment changed from "ASSC" (Aviation Section, Signal Corps) to "AS, USA" (Air Service, United States Army). After July 1, 1920, its personnel became members of the Air Service branch, receiving new commissions. During the war its responsibilities and functions were split between two coordinate agencies, the Division of Military Aeronautics (DMA) and the Bureau of Aircraft Production (BAP), each reporting directly to the Secretary of War, creating a dual authority over military aviation that caused unity of command difficulties.