when did the war department change its name
United States Department of War The War Department existed from August 7, 1789[1] until September 18, 1947, when it split into Department of the Army and Department of the Air Force and joined the Department of the Navy as part of the new joint National Military Establishment (NME), renamed the United States Department of Defense in 1949.
D-Day (military term) The earliest use of these terms by the United States Army that the U.S. Army Center of Military History has been able to find was during World War I.[3] In Field Order Number 9, First Army, American Expeditionary Forces, dated 7 September 1918: "The First Army will attack at H hour on D day with the object of forcing the evacuation of the St. Mihiel Salient."