The United States Department of Defense (DoD) is the federal executive department responsible for coordinating and supervising all agencies and functions of the United States Armed Forces. It is the largest employer in the world, overseeing national defense policy, military planning, and the operations of all service branches. Its headquarters is located at the Pentagon in Arlington, Virginia.
History
The Department of Defense was established by the National Security Act of 1947, which merged the Department of War and the Department of the Navy into the newly created National Military Establishment. In 1949, the establishment was renamed the Department of Defense to reflect unified oversight of all services. The Act also created the positions of Secretary of Defense and Chairman of the Joint Chiefs of Staff.
Mission
The DoD’s mission is to provide the military forces needed to deter war and ensure national security. It is responsible for:
Organizing, training, and equipping the United States Army, United States Navy, United States Marine Corps, United States Air Force, United States Space Force, and United States Coast Guard (when directed).
Supporting combatant commands worldwide.
Overseeing defense policy and resource allocation.
Conducting research, development, and procurement of advanced technology.
Organization
The DoD is composed of:
Office of the Secretary of Defense – civilian leadership, including the Secretary of Defense and Deputy Secretary.
Joint Chiefs of Staff – senior military advisors.
Military Departments – Department of the Army, Department of the Navy (includes the Marine Corps), Department of the Air Force (includes the Space Force).
Unified Combatant Commands – geographic and functional commands that control joint operations.
Defense Agencies and Field Activities – intelligence, logistics, and support organizations.
Leadership
The Secretary of Defense is the principal defense policy advisor to the President and head of the DoD.
The Deputy Secretary of Defense is the second-highest-ranking official.
The military departments are each led by a civilian Secretary (e.g., Secretary of the Army).
Budget
The Department of Defense maintains one of the largest budgets in the U.S. government, funding personnel, operations, procurement, and research. Defense spending has historically represented a significant portion of the federal budget.
Headquarters
The Department of Defense is headquartered at the Pentagon, one of the world’s largest office buildings.