Department of Defense

DoD Logo with collage of military images.

The Department of Defense is responsible for providing the military forces needed to deter war and to protect the security of the United States.  Statutory authority for the Department of Defense is contained in Title 10 of U.S. Code. The Department of Defense's national security roles cover a broad spectrum of conditions ranging from war to peace, including warfighting; supporting foreign internal defense; homeland defense under all kinds of conditions; humanitarian aid; and maintaining relationships with foreign militaries.

The Secretary of Defense is the principal defense policy advisor to the President and is responsible for the formulation of defense policy and for the execution of approved policy. The President exercises command of military forces through the Secretary of Defense and through the commanders of the unified combatant commands. The Secretary is supported by over 1.3 million active duty military members, 669,281 civilian personnel, and another 1.1 million National Guard and Reserve members. The key components of DOD are:

  • Office of the Secretary of Defense (OSD): helps the Secretary plan, advise, and carry out the nation's security policies as directed by both the Secretary of Defense and the President. Five key Under Secretaries work for the Secretary of Defense in critical areas of policy, budgets, force readiness, intelligence and acquisition.
  • Military Services (Army, Navy, Air Force, Marine Corps): Responsible for training and equipping military forces to perform warfighting, peacekeeping and humanitarian/disaster assistance tasks. Military services do not exercise command of military forces when those forces are employed operationally for any purpose. U.S. Special Operations Command also performs "Service-like" train and equip functions for special forces in addition to its Combatant Command functions.
  • Chairman of the Joint Chiefs of Staff: the Chairman serves as the principal military advisor to the President, the National Security Council, and the Secretary of Defense, but is not in the operational chain of command. The Chairman is supported by the "Joint Staff" that coordinates military policy, strategy, planning, operations, and capability requirements.
  • Unified Combatant Commands: command military forces by direction of the Secretary of Defense and the President.  The commands conduct military operations and are composed of at least two military services, organized around either a regional or functional mission. There currently are ten commands: six regional commands (Africa, Central, Europe, Pacific, Northern, Southern) and four functional commands (Joint Forces, Special Operations, Strategic, Transportation).

Organizational chart of Department of Defense