Before 1947, the United States Air Force did not exist as a separate military service. Instead, the responsibility for military aviation was shared between the Army Air Forces and its predecessor organizations for land-based operations, the Navy for sea-based operations from aircraft carriers and amphibious aircraft, and the Marine Corps for close air support of Marine Corps operations. The predecessor organizations leading up to todays U.S. Air Force are:

• Aeronautical Division, Signal Corps (1 August 1907 – 18 July 1914)
• Aviation Section, Signal Corps (18 July 1914 – 20 May 1918)
• Division of Military Aeronautics (20 May 1918 – 24 May 1918)
• U.S. Army Air Service (24 May 1918 – 2 July 1926)
• U.S. Army Air Corps (2 July 1926 – 20 June 1941)
• U.S. Army Air Forces (20 June 1941 – 18 September 1947) .

The National Security Act of 1947 established the Department of the Air Force, which became effective on September 18, 1947, when the first secretary of the Air Force, Stuart Symington, took office. This act created the United States Air Force as an independent service, equal to the US Army and US Navy, and marked the official birthday of the US Air Force.