From Wikipedia:
The predecessor organizations in the Army of today’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 to 24 May 1918)
U.S. Army Air Service (24 May 1918 to 2 July 1926)
U.S. Army Air Corps (2 July 1926 to 20 June 1941) and
U.S. Army Air Forces (20 June 1941 to 18 September 1947)
So that third one only lasted four days?