The Secretary of Defense ( SecDef ) is the leader and chief executive officer of the Department of Defense , the executive department of the Armed Forces of the United States of America .    The Secretary of Defense's power and authority over the United States' military is second only to that of the President and Congress . 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. 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 , for both operational and administrative purposes subject only to the orders of the President, over all Department of Defense forces: the Army , Marine Corps , Navy , and Air Force . This is also extended to the United States Coast Guard during any period of time in which 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 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 exceed 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 , the Attorney General , and the Secretary of the Treasury are generally regarded as the four most important cabinet officials because of the importance of their departments. 
The Army, Navy, and Marine Corps were established in 1775, in concurrence with the American Revolution . The War Department , headed by the Secretary of War , was created by Act of Congress in 1789 and was responsible for both the Army and Navy until the founding of a separate Department of the Navy in 1798.
Based on the experiences of World War II , proposals were soon made on how to more effectively manage the large combined military establishment. The Army generally favored centralization while the Navy had institutional preferences for decentralization and the status quo. The resulting National Security Act of 1947 was largely a compromise between these divergent viewpoints. The Act split the Department of War into the Department of the Army and Department of the Air Force and established the National Military Establishment (NME), presided over by the Secretary of Defense. The Act also separated the Army Air Forces from the Army to become its own branch of service, the United States Air Force . At first, each of the service secretaries maintained cabinet status. The first Secretary of Defense, James Forrestal , who in his previous capacity as Secretary of the Navy had opposed 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.
Powers and functions
The Secretary of Defense, appointed by the President with the advice and consent of the Senate , is by federal law ( 10 U.S.C. ) 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.
As the head of DoD, all officials, employees and service members are "under" the Secretary of Defense. Some of those high-ranking officials, civil and military (outside of OSD and the Joint Staff) are: the Secretary of the Army , Secretary of the Navy , and Secretary of the Air Force , Army Chief of Staff , Commandant of the Marine Corps , Chief of Naval Operations , and Air Force Chief of Staff , Chief of the National Guard Bureau and the Combatant Commanders of the Combatant Commands . All of these high-ranking positions, civil and military, require Senate confirmation.
The Department of Defense is composed of the Office of the Secretary of Defense (OSD), the Joint Chiefs of Staff (JCS) and the Joint Staff (JS), Office of the Inspector General (DODIG), the Combatant Commands , the Military Departments ( Department of the Army (DA), Department of the Navy (DON) & Department of the Air Force (DAF)), the Defense Agencies and DoD Field Activities , the National Guard Bureau (NGB), and such other offices, agencies, activities, organizations, and commands established or designated by law, or by the President or by the Secretary of Defense.
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. 
Office of the Secretary of Defense
The Secretary's principally civilian staff element is called the Office of the Secretary of Defense (OSD) and is composed of the Deputy Secretary of Defense (DEPSECDEF) and five Under Secretaries of Defense in the fields of Acquisition, Technology & Logistics , Comptroller/Chief Financial Officer , Intelligence , Personnel & Readiness , and Policy ; several Assistant Secretaries of Defense ; other directors and the staffs under them.
The name of the principally military staff organization, organized under the Chairman of the Joint Chiefs of Staff, is the Joint Staff (JS).
Awards and decorations
The Defense Distinguished Service Medal (DDSM), the Defense Superior Service Medal (DSSM), the Defense Meritorious Service Medal (DMSM), the Joint Service Commendation Medal (JSCM) and the Joint Service Achievement Medal (JSAM) are awarded, to military personnel for service in joint duty assignments, in the name of the Secretary of Defense. In addition, there is the Joint Meritorious Unit Award (JMUA), which is the only ribbon (as in non-medal) and unit award issued to joint DoD activities, also issued in the name of the Secretary of Defense.
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 only be awarded 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, with the concurrence of the Secretary of State , is the approval authority for the acceptance and wear of NATO medals issued by the Secretary General of NATO and offered to the U.S. Permanent Representative to NATO in recognition of U.S. Service members who meet the eligibility criteria specified by NATO.
As the head of the department, the Secretary of Defense is the chief witness for the congressional committees with oversight responsibilities over the Department of Defense. The most important committees, with respect to the entire department, are the two authorizing committees, the Senate Armed Services Committee (SASC) and the House Armed Services Committee (HASC), and the two appropriations committees, the Senate Appropriations Committee and the House Appropriations Committee .
National Security Council
The Secretary of Defense is a statutory member of the National Security Council .  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.
Role in the military justice system
The Secretary is one of only five or six civilians—the others being the President, the three "service secretaries" (the Secretary of the Army , Secretary of the Navy , and Secretary of the Air Force ), and the Secretary of Homeland Security (when the United States Coast Guard is under the United States Department of Homeland Security and has not been transferred to the Department of the Navy under the Department of Defense)—authorized to act as convening authority in the military justice system for General Courts-Martial ( 10 U.S.C. : article 22, UCMJ ), Special Courts-Martial ( 10 U.S.C. : article 23, UCMJ), and Summary Courts-Martial ( 10 U.S.C. : article 24 UCMJ).
Secretary of Defense is a Level I position of the Executive Schedule , and thus earns a salary of $203,700 per year as of January 2015.
List of Secretaries of Defense
The longest-serving Secretary of Defense is Robert McNamara , who served for a total of 2,595 days. Combining his two non-sequential services as Secretary of Defense, the second longest serving is Donald Rumsfeld , who served just ten days fewer than McNamara. The shortest-serving Secretary of Defense is Elliot Richardson , who was quickly moved to US Attorney General after 114 days due to resignations during the Watergate Scandal (not counting Deputy Secretary of Defense William P. Clements and William Howard Taft IV , who each served a few weeks as temporary/acting Secretary of Defense).
|No.||Portrait||Name||State of Residence||Took Office||Left Office||Days served|| President |
(2595 total) Lyndon B. Johnson 9 Clark M. Clifford Maryland March 1, 1968January 20, 1969  325 10 Melvin R. Laird Wisconsin January 22, 1969January 29, 1973  1468 Richard Nixon 11 Elliot L. Richardson Massachusetts January 30, 1973May 24, 1973  114 – William P. Clements, Jr. 
Acting Texas May 24, 1973July 2, 197339 12 James R. Schlesinger Virginia July 2, 1973November 19, 1975  403467
(870 total) Gerald Ford 13 Donald Rumsfeld Illinois November 20, 1975January 20, 1977  427 14 Harold Brown California January 21, 1977January 20, 1981  1460 Jimmy Carter 15 Caspar Weinberger California January 21, 1981November 23, 1987  2497 Ronald Reagan 16 Frank Carlucci Virginia November 23, 1987January 20, 1989  424 – William Howard Taft IV
Acting Ohio January 20, 1989March 21, 1989  60 George H. W. Bush 17 Richard B. Cheney Wyoming March 21, 1989January 20, 1993  1401 18 Leslie Aspin Wisconsin January 21, 1993February 3, 1994  378 Bill Clinton 19 William J. Perry Pennsylvania February 3, 1994January 23, 1997  / January 24, 19971085 20 William S. Cohen Maine January 24, 1997January 20, 2001  1457 21 Donald Rumsfeld Illinois January 20, 2001December 18, 2006  2158 George W. Bush 22 Robert M. Gates Texas December 18, 2006June 30, 2011  764891
(1,655 total) Barack Obama 23 Leon Panetta California July 1, 2011February 26, 2013  606 24 Chuck Hagel Nebraska February 27, 2013February 17, 2015  720 25 Ash Carter Massachusetts February 17, 2015January 19, 2017  702 26 James Mattis Washington January 20, 2017  Present 315 Donald Trump
Secretary of Defense succession
In Executive Order 13533 of March 1, 2010, President Barack Obama modified the line of succession regarding who would act as Secretary of Defense in the event of a vacancy or incapacitation, thus reversing the changes made by President George W. Bush in Executive Order 13394 as to the relative positions of the Secretaries of the Military Departments. All of the officials in the line of succession are civilians appointed by the President with the advice and consent of the Senate:
Living former Secretaries of Defense
As of December 2017, there are ten living former Secretaries of Defense, the oldest being Harold Brown (1977–1981, born 1927). The most recent Secretary of Defense to die was Melvin Laird (1969–1973), on November 16, 2016.
|Name||Term of office||Date of birth (and age)|
|Donald Rumsfeld||1975–1977, 2001–2006||July 9, 1932|
|Harold Brown||1977–1981||September 19, 1927|
|Frank Carlucci||1987–1989||October 18, 1930|
|Dick Cheney||1989–1993||January 30, 1941|
|William Perry||1994–1997||October 11, 1927|
|William Cohen||1997–2001||August 28, 1940|
|Robert Gates||2006–2011||September 25, 1943|
|Leon Panetta||2011–2013||June 28, 1938|
|Chuck Hagel||2013–2015||October 4, 1946|
|Ash Carter||2015–2017||September 24, 1954 (age 62)|
- List of United States Secretaries of Defense by time in office
- Base Realignment and Closure Commission
- Boeing E-4
- Challenge coin
- Combat Exclusion Policy
- Commission to Assess the Ballistic Missile Threat to the United States
- Continuity of Operations Plan
- CONPLAN 8022-02
- Defense Policy Board Advisory Committee
- Defense Support of Civil authorities
- Department of Defense Directive 2310
- Designated survivor
- Emergency Action Message
- Global Command and Control System
- Gold Codes
- Hamdan v. Rumsfeld
- Joint Worldwide Intelligence Communications System
- Key West Agreement
- McCarran Internal Security Act
- Military Commissions Act of 2006
- Military operation plan
- National Command Authority
- National Industrial Security Program
- National Security Strategy (United States)
- Office of the Secretary of Defense Identification Badge
- Packard Commission
- Permissive Action Link
- Presidential Successor Support System
- Quadrennial Defense Review
- Rules of engagement
- Secretary of Defense Employer Support Freedom Award
- Single Integrated Operational Plan
- State secrets privilege
- Stop-loss policy
- Two-man rule
- Unconventional warfare (United States Department of Defense doctrine)
- United States Foreign Military Financing
- US Commission on National Security/21st Century