Department of Defense

Defense, Department of, executive department of the U.S. government responsible for the recruitment, training, organization, and operation of the armed forces. The National Security Act of 1947 superseded the War Department and brought the previously separate departments of the Army, Navy, and Air Force into the National Military Establishment, which was renamed the Department of Defense in 1949. The secretary of defense, a civilian, heads the department. The civilian staff also includes a deputy secretary and 7 assistant secretaries. Within the military itself, the chiefs of staff of the Army and Air Force, the chief of naval operations, and the commandant of the Marine Corps constitute the Joint Chiefs of Staff (JCS), which has one additional member: the chairman. The JCS advise the secretary of defense, the national security council, and the president on military questions. They are aided by the Joint Staff, composed of some 500 officers from the three services. The department of defense employs over 5 million people.