The mission of the U.S. Department of Defense is to provide the military forces needed to deter war and to protect the security of our country.

Established in 1949, the U.S. Department of Defense is America's oldest and largest g...
See More overnment agency. Secretary of Defense Ash Carter currently heads the organization which employs over 1.4 million active duty service members, 1.1 million National Guard and Reserve forces and 718,000 civilian personnel stationed throughout the United States and around the world. The Defense Department is headquartered at the Pentagon near Washington, D.C.