United States Air Force
The U.S. War Department created the first antecedent of the U.S. Air Force, as a part of the U.S. Army, on 1 August 1907, which through a succession of changes of organization, titles, and missions advanced toward eventual independence 40 years later. In World War II, almost 68,000 U.S. airmen died helping to win the war, with only the infantry suffering more casualties. In practice, the U.S. Army Air Forces (USAAF) was virtually independent of the Army during World War II, and in virtually all ways functioned as an independent service branch, but airmen still pressed for formal independence. The National Security Act of 1947 was signed on 26 July 1947 by President Harry S Truman, which established the Department of the Air Force, but it was not until 18 September 1947, when the first secretary of the Air Force, W. Stuart Symington, was sworn into office that the Air Force was officially formed as an independent service branch.
United States Army Air Forces
Following the successful German invasion of France and the Low Countries in May 1940, Roosevelt asked Congress for a supplemental appropriation of nearly a billion dollars, a production program of 50,000 aircraft a year, and a military air force of 50,000 aircraft (of which 36,500 would be Army). Accelerated programs followed in the Air Corps that repeatedly revised expansion goals, resulting in plans for 84 combat groups, 7,799 combat aircraft, and the annual addition to the force of 30,000 new pilots and 100,000 technical personnel. The accelerated expansion programs resulted in a force of 156 airfields and 152,125 personnel at the time of the creation of the Army Air Forces.
The German invasion of the Soviet Union, occurring only two days after the creation of the Army Air Forces, caused an immediate reassessment of U.S. defense strategy and policy. The need for an offensive strategy to defeat the Axis Powers required further enlargement and modernization of all the military services, including the new AAF. In addition, the invasion produced a new Lend lease partner in Russia, creating even greater demands on an already struggling American aircraft production.