The Department of Defense is America's largest government agency. With our military tracing its roots back to pre-Revolutionary times, the department has grown and evolved with our nation. Our mission is to provide the military forces needed to deter war and ensure our nation's security.
The Army, Marine Corps, Navy, Air Force, Space Force and Coast Guard are the armed forces of the United States. The Army National Guard and the Air National Guard are reserve components of their services and operate in part under state authority.
The Defense Department has 11 combatant commands, each with a geographic or functional mission that provides command and control of military forces in peace and war.