The Department of Defense (DOD) is a federal government agency responsible for providing military forces to deter war and protect the security of the United States. The DOD is the largest employer in the world, with over 1.3 million active-duty service members, as well as civilian personnel and contractors. The DOD is responsible for the administration and operation of the Armed Forces, including the Army, Navy, Air Force, and Marine Corps. The DOD also oversees a number of defense agencies and combatant commands, which are responsible for specific geographic regions or functional areas.