United States Department of War

The United States Department of War, also called the War Department (and occasionally War Office in the early years), was the United States Cabinet department responsible for the operation and maintenance of the United States Army. It also had responsibility for naval affairs from 1794 until the establishment of the Department of the Navy in 1798, and for most non-naval air forces until the creation of the Department of the Air Force on September 18, 1947.

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 throughout its existence.

The War Department existed for 158 years, from August 7, 1789, to September 18, 1947, when, under the National Security Act of 1947, it split into the Department of the Army and the Department of the Air Force (which, together with the Department of the Navy, formed the National Military Establishment). In 1949, the National Military Establishment was renamed the Department of Defense. Provided by Wikipedia