U.S. Department of Defense (DoD)

The U.S. Department of Defense is America's oldest and largest government agency. The mission of the Department of Defense (DoD) is to provide the military forces needed to deter war and to protect the security of the U.S.  The military forces of the Army, Navy, Air Force, and Marines all fall under the DoD. The military maintains one of the largest healthcare systems in the U.S.