The United States Department of Defense (DoD) is the federal department responsible for providing the military forces needed to deter war and protect the security of the United States. It is the largest employer in the world, with over 3 million employees. The DoD is headed by the Secretary of Defense, who is a member of the President's Cabinet. The DoD is responsible for the organization, training, equipping, and providing for the welfare of the U.S. Armed Forces. It also provides support to the National Guard and Reserve forces.