United States Secretary of Defense
The United States Secretary of Defense (SecDef) is the civilian official with direct authority over all the military and civilian personnel of the United States Department of Defense. Robert M. Gates is the incumbent.
Originally, the United States had a separate Secretary of War and Secretary of the Navy, heading separate cabinet-level departments.
With the passage of the National Security Act of 1947, the Department superseded the War Department and Department of the Navy. This Act created the Office of the Secretary of Defense, moved the heads of the War and Navy Departments to rank equivalent to Assistant Secretary of Defense, and created a Secretary of the Air Force.