<P> In wartime, the Department has authority over the Coast Guard, which is under the control of the Department of Homeland Security (DHS) in peacetime . Prior to the creation of DHS, the Coast Guard was under the control of the Department of Transportation, and earlier under the Department of the Treasury . According to the U.S. Code, the Coast Guard is at all times considered one of the five armed services of the United States . During times of declared war (or by Congressional direction), the Coast Guard operates as a part of the Navy; this has not happened since World War II, but members have served in undeclared wars and conflicts since then while the service remained in its peacetime department . </P> <P> The Pentagon, in Arlington County, Virginia, across the Potomac River from Washington, D.C., is the Department's headquarters . The Department is protected by the Pentagon Force Protection Agency, which ensures law enforcement and security for the Pentagon and various other jurisdictions throughout the National Capital Region (NCR). </P> <P> The President of the United States is, according to the Constitution, the Commander - in - Chief of the U.S. Armed Forces and Chief Executive of the Federal Government . The Secretary of Defense is the "Principal Assistant to the President in all matters relating to the Department of Defense", and is vested with statutory authority (10 U.S.C. § 113) to lead the Department and all of its component agencies, including military command authority second only to the President . </P> <P> The President and the Secretary of Defense exercise authority and control of the Armed Forces through two distinct branches of the chain of command . One branch (10 U.S.C. § 162) runs from the President, through the Secretary of Defense, to the Combatant Commanders for missions and forces assigned to their commands . The other branch, used for purposes other than operational direction of forces assigned to the combatant commands, runs from the President through the Secretary of Defense to the Secretaries of the Military Departments, i.e., the Secretary of the Army (10 U.S.C. § 3013), the Secretary of the Navy (10 U.S.C. § 5013), and the Secretary of the Air Force (10 U.S.C. § 8013). The Military Departments, organized separately within the Department, operate under the authority, direction, and control of the Secretary of that Military Department . The Secretaries of the Military Departments exercise authority through their respective Service Chiefs (i.e., Chief of Staff of the Army, Commandant of the Marine Corps, Chief of Naval Operations, and Chief of Staff of the Air Force) over forces not assigned to a Combatant Command . The Service Chiefs, except as otherwise prescribed by law, perform their duties under the authority, direction, and control of the Secretaries of their respective Military Departments, to whom they are directly responsible . </P>

Who is the principal assistant to the president in all matters relating to the dod