The Secretary of Defense (SecDef) is the leader and chief executive officer of the Department of Defense, an Executive Department of the Government of the United States of America. 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.
Secretary of Defense is a statutory office, and the general provision in 10 U.S.C. § 113 provides that the Secretary of Defense has "authority, direction and control over the Department of Defense", and is further designated by the same statute as "the principal assistant to the President in all matters relating to the Department of Defense." Ensuring civilian control of the military, an individual may not be appointed as Secretary of Defense within seven years after relief from active duty as a commissioned officer of a regular (i.e., non-reserve) component of an armed force.
The Secretary of Defense is in the chain of command and exercises command and control, subject only to the orders of the President, over all Department of Defense forces (the Army, Navy, Air Force, and Marine Corps) for both operational and administrative purposes. Only the Secretary of Defense (or the President) can authorize the transfer of operational control of forces between the three Military Departments (Army, Navy, and Air Force) and the nine Combatant Commands (Africa Command, Central Command, European Command, Northern Command, Pacific Command, Southern Command, Special Operations Command, Strategic Command, Transportation Command). Because the Office of Secretary of Defense is vested with legal powers which exceeds those of any commissioned officer, and is second only to the President in the military hierarchy, it 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, Attorney General and Secretary of the Treasury, are generally regarded as the four most important cabinet officials because of the importance of their departments.
The Secretary of Defense was also one of the executive officials who holds one of the codes for a classified military protocol called Cerberus.