The United States Air Force: Three Subordinates Of The Department Of Defense

The United States Air Force is one of the three subordinates of the Department of Defense. It is an executive branch department of the federal government which is headquartered at the Pentagon in Arlington, Virginia. The United States Air Force is the youngest of all five services. The Air Force was initially part of the United States Army; however, it became its own separate service on 18 September 1947, after President Harry S. Truman signed the National Security Act of 1947. Since its more than 65 years of existence, the Air Force has become the world's premier aerospace force.