Leader of the Armed Forces of the United States
The United States secretary of defense (SecDef) is the head of the United States Department of Defense, the executive department of the U.S. Armed Forces, and is a high ranking member of the federal cabinet. The secretary of defense's position of command and authority over the military is second only to that of the president of the United States, who is the commander-in-chief. This position corresponds to what is generally known as a defense minister in many other countries. The secretary of defense is appointed by the president with the advice and consent of the Senate, and is by custom a member of the Cabinet and by law a member of the National Security Council.
The secretary of defense is a statutory office, and the general provision in 10 U.S.C. § 113 provides that "subject to the direction of the President", its occupant has "authority, direction, and control over the Department of Defense". The same statute further designates the secretary as "the principal assistant to the President in all matters relating to the Department of Defense". To ensure civilian control of the military, no one may be appointed as the secretary of defense within seven years of serving as a commissioned officer of a regular military component (i.e., non-reserve) without a waiver from Congress.
Subject only to the orders of the president, the secretary of defense is in the chain of command and exercises command and control, for both operational and administrative purposes, over all service branches administered by the Department of Defense – the Army, Marine Corps, Navy, Air Force, and Space Force – as well as the Coast Guard when its command and control is transferred to the Department of Defense. Only the secretary of defense (or the president or Congress) can authorize the transfer of operational control of forces between the three military departments (Department of the Army, the Navy, and the Air Force) and the eleven Unified Combatant Commands. Because the secretary of defense is vested with legal powers that exceed those of any commissioned officer, and is second only to the president in the military hierarchy, its incumbent has sometimes unofficially been referred to as "deputy commander-in-chief". The chairman of the Joint Chiefs of Staff is the principal military adviser to the secretary of defense and the president; while the chairman may assist the secretary and president in their command functions, the chairman is not in the chain of command.