In 1943, during World War II, the make-up of a post- war Air Force was already being planned, however. Supporters of the idea that the Air Force should be a separate branch of the service, with its own autonomy, set out to convince senior military planners of the idea. Under the leadership of General Henry "Hap" Arnold, the Army Air Force was becoming increasingly independent. In 1944, the planners released the AAF's "initial plan for the post-war Air Force."  

The result did not become a reality until July 12, 1947, when President Harry S. Truman signed the National Security Act, making the United States Air Force a separate branch of the service. The signing of the papers took place aboard the President's personal airplane, the "Sacred Cow."