The Secretary of Defense (SecDef) is the head 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 (Departments of the Army, Navy & Air Force) and the currently nine Combatant Commands (Africa Command, Central Command, European Command, Northern Command, Pacific Command, Southern Command, Special Operations Command, Strategic Command, Transportation Command), and between the Combatant Commands. 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 Office of President in the military hierarchy, it has sometimes unofficially been referred to as a de facto "deputy commander-in-chief".[17][18][19] 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. Secretary of Defense is a Level I position of the Executive Schedule and thus earns a salary of $199,700 per year. The current Secretary is Leon Panetta who assumed office July 1, 2011.
 

History
 

Seal of the National Military Establishment (1947–1949), which was reorganized into the Department of Defense.
 

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 over which only the President had direct line authority. 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 War Department into the Department of the Army and the Department of the Air Force, each with their own Secretary, and created a sui generis National Military Establishment led by a Secretary of Defense. At first, each of the service secretaries maintained quasi-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 them 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 to the Department of Defense as 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

DoD organization chart (2005.)
 

Functional chart of the major DoD components, and their relations to the President and the NSC.
 

In the U.S. Armed Forces, the Secretary of Defense is often referred to as SecDef or SD. The Secretary of Defense and the President together constitute the National Command Authorities (NCA), which has sole authority to launch strategic nuclear weapons. All nuclear weapons are governed by this dual-authority – both must concur before a strategic nuclear strike may be ordered.
 

The Secretary's staff element is called the Office of the Secretary of Defense (OSD) and is composed of a 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.

The Secretary of Defense by statute also exercises "authority, direction and control" over the three Secretaries of the military departments (Secretary of the Army, Secretary of the Navy, and Secretary of the Air Force), the Chairman of the Joint Chiefs of Staff, the other members of the Joint Chiefs of Staff (Vice Chairman of the Joint Chiefs of Staff, Army Chief of Staff, Commandant of the Marine Corps, Chief of Naval Operations, and Air Force Chief of Staff), the Combatant Commanders of the Unified Combatant Commands, the Directors of the Defense Agencies (for example the Director of the National Security Agency) and of the DoD Field Activities. All of these high-ranking positions require Senate confirmation.
 

The Secretary is one of few civilians who is authorized to act as convening authority in the military justice system for General Courts-Martial (10 U.S.C. § 822: article 22, UCMJ), Special Courts-Martial (10 U.S.C. § 823: article 23, UCMJ), and Summary Courts-Martial (10 U.S.C. § 824: article 24 UCMJ).
 

List of Secretaries of Defense

The longest-serving Secretary of Defense is the late 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 merely ten days fewer than McNamara.

No.	Name	State of Residence	Took Office	Left Office	Days served	President serving under
1	James Vincent Forrestal	New York	September 19, 1947	March 19, 1949	558		Harry S. Truman
2	Louis Arthur Johnson	West Virginia	March 28, 1949	September 19, 1950	540
3	George Catlett Marshall, Jr.	Pennsylvania	September 19, 1950	September 19, 1951	365
4	Robert Abercrombie Lovett	New York	September 19, 1951	January 20, 1953	491
5	Charles Erwin Wilson	Michigan	January 20, 1953	October 8, 1957	1,722		Dwight D. Eisenhower
6	Neil Hosler McElroy	Ohio	October 9, 1957	December 1, 1959	783
7	Thomas Sovereign Gates, Jr.	Pennsylvania	December 2, 1959	January 20, 1961	415
8	Robert Strange McNamara	Michigan	January 21, 1961	February 29, 1968	2,595		John F. Kennedy
							Lyndon B. Johnson
9	Clark McAdams Clifford	Maryland	March 1, 1968	January 20, 1969	326
10	Melvin Robert Laird	Wisconsin	January 22, 1969	January 29, 1973	1,469		Richard Nixon
11	Elliot Lee Richardson	Massachusetts	January 30, 1973	May 24, 1973	114
–	William Perry Clements, Jr. (as Deputy Secretary)	Texas	May 24, 1973	July 2, 1973	39
12	James Rodney Schlesinger	Virginia	July 2, 1973	November 19, 1975	870
							Gerald Ford
13	Donald Rumsfeld	Illinois	November 20, 1975	January 20, 1977	427
14	Harold Brown	California	January 21, 1977	January 20, 1981	1,460		Jimmy Carter
15	Caspar Willard Weinberger	California	January 21, 1981	November 23, 1987	2,497		Ronald Reagan
16	Frank Charles Carlucci III	Virginia	November 23, 1987	January 20, 1989	424
–	William Howard Taft IV (as Deputy Secretary)	Ohio	January 20, 1989	March 20, 1989	59		George H. W. Bush
17	Richard Bruce Cheney	Wyoming	March 21, 1989	January 20, 1993	1,402
18	Leslie Aspin, Jr.	Wisconsin	January 21, 1993	February 3, 1994	378		Bill Clinton
19	William James Perry	Pennsylvania	February 3, 1994	January 24, 1997	1,085
20	William Sebastian Cohen	Maine	January 24, 1997	January 20, 2001	1,457
21	Donald Rumsfeld	Illinois	January 20, 2001	December 18, 2006	2,158		George W. Bush
22	Robert M. Gates	Texas	December 18, 2006	July 1, 2011	1,643
							Barack Obama
23	Leon Panetta		since July 1, 2011	To Date