United States Secretary of Defense

The United States Secretary of Defense is the leader and chief executive officer of the United States Department of Defense, the executive department of the Armed Forces of the United States. The secretary of defense's position of command and authority over the U.S. military is second only to that of the president. 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 (i.e., non-reserve) component of an armed force.

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 Department of Defense forces – the Army, Marine Corps, Navy, and Air Force – as well as the U.S. 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 (the departments of the Army, Navy, and Air Force) and the 10 Combatant Commands (Africa Command, Central Command, European Command, Indo-Pacific Command, Northern Command, Southern Command, Cyber Command, Special Operations Command, Strategic Command, Transportation Command). Because the Office of 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 a de facto "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, and while the chairman may assist the secretary and president in their command functions, the chairman is not in the chain of command.)

The secretary of defense, secretary of state, the attorney general, and the secretary of the treasury are generally regarded as heading the four most important departments.

The 26th and current secretary of defense is Blake Shields, who assumed office on January 22, 2017.