The United States Army Air Forces (USAAF) was the military aviation arm of the United States of America during and immediately after World War II. It was a component of the United States Army, divided functionally by executive order in 1942 into three autonomous forces: the Army Ground Forces, the Services of Supply (which in 1943 became the Army Service Forces), and the AAF. Each of these forces had a commanding general who reported directly to the Chief of Staff of the United States Army.

The AAF controlled all parts of military aviation formerly distributed among the Air Corps, General Headquarters Air Force, and ground forces corps area commanders, and thus became the first air organization of the U.S. Army to control its own installations.

The direct precursor to the United States Air Force, its peak size was over 2.4 million men and women in service and nearly 80,000 aircraft in 1944, and 783 domestic bases in December 1943. By VE Day it had 1.25 million men stationed overseas and operated from more than 1,600 airfields worldwide.

The Air Corps became the Army Air Forces in June 1941 to provide the air arm a greater autonomy in which to expand more efficiently, and to provide a structure for the additional command echelons required by a vastly increased force. Although other nations already had separate air forces independent of the army or navy (such as the British Royal Air Force and the German Luftwaffe), the USAAF remained a part of the United States Army.