First of all, let me introduce the reason for my question. In the obituary of American historian Otto Pflanze (1918-2007) we read: "...he interrupted his graduate training in 1942 to serve as 1st lieutenant in the Air Corps of the U.S. Army until 1946." Now it's not hard to research that the predecessors of the US Air Force (1947-) were called the US Army Air Corps (USAAC) from 1926 to 1941 and the US Army Air Forces (USAAF) from 1941 to 1947. So it seems the obituary is wrong in this regard - at the time given, Pflanze would have served in the Forces, not the Corps. But in the Wikipedia article about the USAAC, we can read: "The Air Corps ceased to have an administrative structure after 9 March 1942, but as "the permanent statutory organization of the air arm, and the principal component of the Army Air Forces," the overwhelming majority of personnel assigned to the AAF were members of the Air Corps." "The Congress did not dis-establish the Army Air Corps as a combat arm until 26 July 1947, when the National Security Act of 1947 (61 Stat. 502) became law. Most members of the Army Air Forces also remained members of the Air Corps. In May 1945, 88 percent of officers serving in the Army Air Forces were commissioned in the Air Corps, while 82 percent of enlisted members assigned to AAF units and bases had the Air Corps as their combat arm branch." I don't exactly understand. Members of the USAAC remained such even in the USAAF - ok. But why would someone who started serving after 1941 become an officer of the USAAC, not the USAAF? And if so - until when where officiers of the USAAC commissioned? Until 9 March 1942? Or maybe even until 1947...?