What's different between USAAF and USAAC ? I know USAAC is forerunner of USAAF, but some WW2 books bear both of them in the same period. If USAAC is forerunner of USAAF then USAAC should quit when USAAF comes ?? Thanks.
If I'm not mistaken they are one and the same group. It was the Army Air Corps until the giant buildup for the war, and then when they actually went to war in 1942 they had morphed into the Army Air Forces. In that case it could be that in that instance, it is possible they co-existed as the transformation was completed. Here is a link which shows it actually occurred in June of 1941, before Pearl Harbor. I was under the impression it was later. My mistake. Goto: http://www.aafha.org/aaf_or_aircorps.html
The AAC continued to exist as a subordinate element of the Army Air Forces until 1947. Apparently, officers were commission into the AAC although they served in the AAF. Many reports that I have from mission folders in 1944 are signed in the form: John Doe 1st Lt. Air Corps There is a long discussion regarding USAAC vs USAAF here: USAAC or USAAF?
Both the USAAC and the USAAF ceased to exist with the establishment of the US Air Force as an independent branch in 1947.
The Army has always been broken down into series of smaller "corps" these are also what is referred to as "branches" such as: Infantry, Artillery, Tank, Engineer, Medical, Transportation etc... During WW2 a person serving in the "US Army Airforce" would be part of the "Army Air Corps".