The Department of Defence (DoD) is a United States government agency responsible for coordinating and supervising all agencies and functions related to national security and the military. It oversees the U.S. Armed Forces, which includes the Army, Navy, Air Force, Marine Corps, and Space Force. The DoD's primary mission is to protect the country and its interests through military readiness and strategic planning. The DoD is headed by the Secretary of Defense, who is a member of the President's Cabinet. The department also works closely with other government entities, such as the Department of Homeland Security, to ensure a comprehensive approach to national security.