The National Security Act of 1947 established a National Military Establishment headed by a Secretary of Defense with three executive departments. The Department of War became the Department of the Army. Congress made the army air forces a separate service under a new Department of the Air Force. The navy and marine corps continued under the Department of the Navy. The law also established the Joint Chiefs of Staff, Munitions Board, and Research and Development Board, within the new organization.
The Secretary of Defense became a member of the Cabinet in place of the secretaries of the military services. He exercised general direction of his agency. The secretaries of the Army, Navy and Air Force administered their own departments.