1907-1947 -- The Lineage of the US Air Force Aeronautical Division, US Signal Corps 1 August 1907 - 18 July 1914 Aviation Section, US Signal Corps 18 July 1914 - 20 May 1918 Division of Military Aeronautics 20 May 1918 - 24 May 1918 Air Service 24 May 1918 - 2 July 1926 Air Corps* 2 July 1926 - 18 September 1947 Army Air Forces 20 June 1941 - 18 September 1947 United States Air Force 18 September 1947 *The Air Corps became a subordinate element of the Army Air Forces on 20 June 1941, and it continued to exist as a combat arm of the Army until 1947.