After WWII, the U.S. Department of War was renamed Department of Defense

The United States Department of War, was originally responsible for the operation and maintenance of the United States Army. The War Department also bore responsibility for naval affairs until the establishment of the Navy Department in 1798 and for most land-based air forces until the creation of the Department of the Air Force in 1947. TheSecretary of War headed the war department throughout its existence.

The War Department existed from 1789 until September 18, 1947, when it split into Department of the Army and Department of the Air Force and joined theDepartment of the Navy as part of the new joint National Military Establishment(NME), renamed the United States Department of Defense in 1949.

The Secretary of War, a civilian with such responsibilities as finance and purchases and a minor role in directing military affairs, headed the War Department.