Final answer:
The authority, direction, and control over the DoD and its component agencies are under the Secretary of Defense and the Commander in Chief, the President. They are responsible for overseeing the military, which includes all branches of the U.S. armed forces and for ensuring national security, following the constitutional principle of civilian control of the military.
Step-by-step explanation:
The functions in the Department of Defense (DoD) and its component agencies are performed under the authority, direction, and control of the Secretary of Defense and ultimately the President of the United States, who is the Commander in Chief of the armed forces. Each cabinet department, including the DoD, has a head known as a secretary, who is appointed by the president and confirmed by the Senate. Whereas the Secretary of Defense is a civilian overseeing the entire DoD, including the Army, Navy, Marine Corps, Air Force, and the Coast Guard, the highest uniformed officer is the Chairman of the Joint Chiefs of Staff, who must report to civilian authorities, following the constitutional principle of civilian control over the military.
In accordance with the National Security Act of 1947 and its subsequent amendments, the DoD was reorganized to provide efficient military readiness and to consolidate the military branches under unified control. The Executive Branch includes crucial entities such as the National Security Council and the Central Intelligence Agency (CIA) which also play a role in the nation's defense and security. The Department of Defense, under the guidance and oversight of the president, is responsible for protecting the territory of the United States from various threats, maintaining military readiness, and conducting foreign policy endeavors through its defense and intelligence agencies.