The modern-day USAF traces its roots to the Aeronautical Division of the US Army's Signal Corps, established on 1 August 1907. Its first aircraft was a Wright Flyer. On 18 July 1914, the name was changed to Aviation Section, still within the Signal Corps, and remained so well into World War I when, on 20 May 1918, it became the US Army Air Service. The first US-trained American Expeditionary Forces air ace was Captain Edward V. Rickenbacker, who, by the end of the conflict, became the leading Air Service ace with 26.33 aerial victories.

Between wars another change of name occurred, when today's USAF was renamed the US Army Air Corps on 2 July 1926. Prior to America's entry into World War II, yet another renaming took place on 20 June 1941 and the Air Corps became US Army Air Forces (USAAF).

The wartime USAAF, fed by the giant industrial machine of the American heartland, eventually had nearly 60,000 warplanes and reached its peak strength of 2,372,292 personnel in 1944. The B-17 Flying Fortress, B-29 Superfortress and P-51 Mustang were among the best-known warplanes and played vital roles in defeating the Axis. A Superfortress brought the dawn of the atomic age with the 6 August 1945 bombing of Hiroshima.