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 DoD-administered service branches – 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.[11][12][13][14][15] 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.[11] 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".[16][17][18] 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.[19]
The secretary of state, the secretary of the treasury, the secretary of defense, and the attorney general are generally regarded as the four most important (and are officially the four most senior and oldest) cabinet officials because of the size and importance of their respective departments.[20]
The current secretary of defense is Pete Hegseth, who was nominated by president-elect Donald Trump and was confirmed by the Senate on January 25, 2025.
A new title was coined by the Act for the head of the NME: Secretary of Defense. At first, each of the service secretaries maintained cabinet status. The first secretary of defense, James Forrestal, who in his previous capacity as the secretary of the Navy had opposed the creation of the new position, found it difficult to exercise authority over the other branches with the limited powers his office had at the time. To address this and other problems, the National Security Act was amended in 1949 to further consolidate the national defense structure in order to reduce interservice rivalry, directly subordinate the secretaries of the Army, the Navy and the Air Force to the secretary of defense in the chain of command, and rename the National Military Establishment as the Department of Defense, making it one Executive Department. The position of the deputy secretary of defense, the number two position in the department, was also created at this time.
The general trend since 1949 has been to further centralize management in the Department of Defense, elevating the status and authorities of civilian OSD appointees and defense-wide organizations at the expense of the military departments and the services within them. The last major revision of the statutory framework concerning the position was done in the Goldwater–Nichols Department of Defense Reorganization Act of 1986. In particular, it elevated the status of joint service for commissioned officers, making it in practice a requirement before appointments to general officer and flag officer grades could be made.
As the secretary of defense is a civilian position intended to be independent of the active-duty leadership, a secretary is required to have been retired from service for at least seven (originally ten) years unless a waiver is approved by Congress.[21] Since the creation of the position in 1947, such a waiver has been approved only three times, for Army general George Marshall in 1950, Marine Corps General Jim Mattis in 2017, and retired Army general Lloyd Austin in 2021.[22][23]
The secretary of defense, appointed by the president with the advice and consent of the Senate, is by federal law (10 U.S.C.§ 113) the head of the Department of Defense, "the principal assistant to the President in all matters relating to Department of Defense", and has "authority, direction and control over the Department of Defense". Because the Constitution vests all military authority in Congress and the president, the statutory authority of the secretary of defense is derived from their constitutional authorities. Since it is impractical for either Congress or the president to participate in every piece of Department of Defense affairs, the secretary of defense and the secretary's subordinate officials generally exercise military authority.
Department of Defense Directive 5100.01 describes the organizational relationships within the department and is the foundational issuance for delineating the major functions of the department. The latest version, signed by former secretary of defense Robert Gates in December 2010, is the first major re-write since 1987.[24][25]
The DDSM is analogous to the distinguished services medals issued by the military departments (i.e. Army Distinguished Service Medal, Navy Distinguished Service Medal & Air Force Distinguished Service Medal), the DSSM corresponds to the Legion of Merit, the DMSM to the Meritorious Service Medal, the JSCM to the service commendation medals, and the JSAM to the achievement medals issued by the services. While the approval authority for DSSM, DMSM, JSCM, JSAM and JMUA is delegated to inferior DoD officials: the DDSM can be awarded only by the secretary of defense.
Recommendations for the Medal of Honor (MOH), formally endorsed in writing by the secretary of the military department concerned and the chairman of the Joint Chiefs of Staff, are processed through the under secretary of defense for personnel and readiness, and such recommendations be must approved by the secretary of defense before it can be handed over to the president, who is the final approval authority for the MOH, although it is awarded in the name of Congress.
The secretary of defense is a statutory member of the National Security Council.[27] As one of the principals, the secretary along with the vice president, secretary of state and the assistant to the president for national security affairs participates in biweekly Principals Committee (PC) meetings, preparing and coordinating issues before they are brought before full NSC sessions chaired by the president.
The longest-serving secretary of defense is Robert McNamara, who served for a total of 7years, 39 days. Combining his two non-sequential services as the secretary of defense, the second-longest serving is Donald Rumsfeld, who served just ten days fewer than McNamara. The second-longest unbroken tenure was Caspar Weinberger's, at 6years, 306 days.
For precursors to this position prior to the establishment of the Department of Defense, see the lists of secretaries of the Navy and secretaries of war prior to 1947.
On December 10, 2020, President Donald Trump modified the order of succession for the office of Secretary of Defense in Executive Order 13963. The order of succession is:[66]
^According to the Executive Order precedence states – in layman’s terms – that appointees designated the same succession number are determined by the order in which the date they were appointed (senate confirmed) to their position. However appointees designated the same succession number and have the same appointment (senate confirmed) date shall be determined by the order in which they have taken the oath to serve in that office.
^See 10 U.S.C.§ 113. The National Security Act of 1947 originally required an interval of ten years after relief from active duty, which was reduced to seven years by Sec. 903(a) of the 2008 National Defense Authorization Act. In 1950 Congress passed special legislation (Pub. Law 81-788) to allow George C. Marshall to serve as Secretary of Defense while remaining a commissioned officer on the active list of the Army (Army regulations kept all five-star generals on active duty for life), but warned:
It is hereby expressed as the intent of the Congress that the authority granted by this Act is not to be construed as approval by the Congress of continuing appointments of military men to the office of Secretary of Defense in the future. It is hereby expressed as the sense of the Congress that after General Marshall leaves the office of Secretary of Defense, no additional appointments of military men to that office shall be approved.
^Korb, Lawrence J.; Ogden, Pete (October 31, 2006). "Rumsfeld's Management Failures". Center for American Progress. Archived from the original on October 22, 2017. Retrieved January 6, 2012.
^Cantwell, Gerald T. (1997). Citizen Airmen: A History of the Air Force Reserve 1946–1994. DIANE Publishing. p. 252. ISBN9781428991620. In June 1973, Representative O. C. Fisher complained to William P. Clements, Jr., acting Secretary of Defense, that the authority, responsibility, and, consequently, effectiveness of the chiefs of the various reserve components seemed to be eroding.
^"II. Secretaries of Defense"(PDF). Washington Headquarters Services – Pentagon Digital Library. p. 9. Archived from the original(PDF) on February 11, 2017. Retrieved February 8, 2017. (Deputy Secretary of Defense William H. Taft served as acting secretary of defense from 20 January 1989 until 21 March 1989).
^"II. Secretaries of Defense"(PDF). Washington Headquarters Services – Pentagon Digital Library. p. 10. Archived from the original(PDF) on February 11, 2017. Retrieved February 8, 2017. Sworn in as secretary of defense on 3 February 1994 and served until 24 January 1997.