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United States Secretary of Defense

Updated: Wikipedia source

United States Secretary of Defense

The United States secretary of defense (SecDef), secondarily titled the secretary of war (SecWar), is the head of the United States Department of Defense (DoD), the executive department of the U.S. Armed Forces, and is a high-ranking member of the cabinet of the United States. The secretary of defense's position of command and authority over the military is second only to that of the president of the United States, who is the commander-in-chief. This position corresponds to what is generally known as a defense minister in many other countries. The president appoints the secretary of defense 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. 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. 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. To ensure civilian control of the military, U.S. law provides that the secretary of defense cannot have served as an active-duty commissioned officer in the military in the preceding seven years except for generals and admirals, who cannot have served on active duty within the previous ten years. Congress can legislatively waive this restriction and has done so three times, for George C. Marshall Jr., James N. Mattis, and Lloyd J. Austin III. 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. 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". 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. The current secretary of defense is Pete Hegseth, who was nominated by President Donald Trump and was confirmed by the Senate on January 25, 2025.

Infobox

Seat
The Pentagon, Arlington County, Virginia
Style
Mr. Secretary (informal)The Honorable (formal)
Deputy
Deputy Secretary of Defense
Salary
Executive Schedule, level I
Website
war.gov
Appointer
The presidentwith Senate advice and consent
Formation
September 17, 1947 (1947-09-17)
Member of
CabinetNational Security Council
Precursor
mw- Secretary of War Secretary of the Navy
Reports to
President of the United States
Succession
Sixth
Term length
No fixed term
Abbreviation
SecDef or SECDEF
First holder
James Forrestal
Constituting instrument
10 U.S.C. § 113

Tables

· List of secretaries of defense
James Forrestal
James Forrestal
No.
1
Name
James Forrestal
Start
September 17, 1947
End
March 28, 1949
Duration
1 year, 192 days
Party
Democratic
Home State
New York
President(s)
Harry S. Truman(1945–1953)
Louis A. Johnson
Louis A. Johnson
No.
2
Name
Louis A. Johnson
Start
March 28, 1949
End
September 19, 1950
Duration
1 year, 175 days
Party
Democratic
Home State
West Virginia
George C. Marshall
George C. Marshall
No.
3
Name
George C. Marshall
Start
September 21, 1950
End
September 12, 1951
Duration
356 days
Party
Independent
Home State
Pennsylvania
Robert A. Lovett
Robert A. Lovett
No.
4
Name
Robert A. Lovett
Start
September 17, 1951
End
January 20, 1953
Duration
1 year, 125 days
Party
Republican
Home State
New York
Charles Erwin Wilson
Charles Erwin Wilson
No.
5
Name
Charles Erwin Wilson
Start
January 28, 1953
End
October 8, 1957
Duration
4 years, 253 days
Party
Republican
Home State
Michigan
President(s)
Dwight D. Eisenhower(1953–1961)
Neil H. McElroy
Neil H. McElroy
No.
6
Name
Neil H. McElroy
Start
October 9, 1957
End
December 1, 1959
Duration
2 years, 53 days
Party
Republican
Home State
Ohio
Thomas S. Gates Jr.
Thomas S. Gates Jr.
No.
7
Name
Thomas S. Gates Jr.
Start
December 2, 1959
End
January 20, 1961
Duration
1 year, 49 days
Party
Republican
Home State
Pennsylvania
Robert McNamara
Robert McNamara
No.
8
Name
Robert McNamara
Start
January 21, 1961
End
February 29, 1968
Duration
7 years, 39 days
Party
Republican
Home State
Michigan
President(s)
John F. Kennedy(1961–1963)
Clark Clifford
Clark Clifford
No.
9
Name
Clark Clifford
Start
March 1, 1968
End
January 20, 1969
Duration
325 days
Party
Democratic
Home State
Maryland
President(s)
Lyndon B. Johnson(1963–1969)
Melvin Laird
Melvin Laird
No.
10
Name
Melvin Laird
Start
January 22, 1969
End
January 29, 1973
Duration
4 years, 7 days
Party
Republican
Home State
Wisconsin
President(s)
Richard Nixon(1969–1974)
Elliot Richardson
Elliot Richardson
No.
11
Name
Elliot Richardson
Start
January 30, 1973
End
May 24, 1973
Duration
114 days
Party
Republican
Home State
Massachusetts
Bill ClementsActing
Bill ClementsActing
No.
Name
Bill ClementsActing
Start
May 24, 1973
End
July 2, 1973
Duration
39 days
Party
Republican
Home State
Texas
James R. Schlesinger
James R. Schlesinger
No.
12
Name
James R. Schlesinger
Start
July 2, 1973
End
November 19, 1975
Duration
2 years, 140 days
Party
Republican
Home State
Virginia
President(s)
Richard Nixon(1969–1974)
Donald Rumsfeld
Donald Rumsfeld
No.
13
Name
Donald Rumsfeld
Start
November 20, 1975
End
January 20, 1977
Duration
1 year, 61 days
Party
Republican
Home State
Illinois
President(s)
Gerald Ford(1974–1977)
Harold Brown
Harold Brown
No.
14
Name
Harold Brown
Start
January 20, 1977
End
January 20, 1981
Duration
4 years, 0 days
Party
Democratic
Home State
California
President(s)
Jimmy Carter(1977–1981)
Caspar Weinberger
Caspar Weinberger
No.
15
Name
Caspar Weinberger
Start
January 21, 1981
End
November 23, 1987
Duration
6 years, 306 days
Party
Republican
Home State
California
President(s)
Ronald Reagan(1981–1989)
Frank Carlucci
Frank Carlucci
No.
16
Name
Frank Carlucci
Start
November 23, 1987
End
January 20, 1989
Duration
1 year, 58 days
Party
Republican
Home State
Virginia
William Howard Taft IVActing
William Howard Taft IVActing
No.
Name
William Howard Taft IVActing
Start
January 20, 1989
End
March 21, 1989
Duration
60 days
Party
Republican
Home State
Ohio
President(s)
George H. W. Bush(1989–1993)
Dick Cheney
Dick Cheney
No.
17
Name
Dick Cheney
Start
March 21, 1989
End
January 20, 1993
Duration
3 years, 305 days
Party
Republican
Home State
Wyoming
Les Aspin
Les Aspin
No.
18
Name
Les Aspin
Start
January 20, 1993
End
February 3, 1994
Duration
1 year, 14 days
Party
Democratic
Home State
Wisconsin
President(s)
Bill Clinton(1993–2001)
William Perry
William Perry
No.
19
Name
William Perry
Start
February 3, 1994
End
January 24, 1997
Duration
2 years, 356 days
Party
Democratic
Home State
Pennsylvania
William Cohen
William Cohen
No.
20
Name
William Cohen
Start
January 24, 1997
End
January 20, 2001
Duration
3 years, 362 days
Party
Republican
Home State
Maine
Donald Rumsfeld
Donald Rumsfeld
No.
21
Name
Donald Rumsfeld
Start
January 20, 2001
End
December 18, 2006
Duration
5 years, 332 days(7 years, 29 days total)
Party
Republican
Home State
Illinois
President(s)
George W. Bush(2001–2009)
Robert Gates
Robert Gates
No.
22
Name
Robert Gates
Start
December 18, 2006
End
June 30, 2011
Duration
4 years, 194 days
Party
Republican
Home State
Texas
President(s)
George W. Bush(2001–2009)
Leon Panetta
Leon Panetta
No.
23
Name
Leon Panetta
Start
July 1, 2011
End
February 26, 2013
Duration
1 year, 240 days
Party
Democratic
Home State
California
President(s)
Barack Obama(2009–2017)
Chuck Hagel
Chuck Hagel
No.
24
Name
Chuck Hagel
Start
February 27, 2013
End
February 17, 2015
Duration
1 year, 355 days
Party
Republican
Home State
Nebraska
Ash Carter
Ash Carter
No.
25
Name
Ash Carter
Start
February 17, 2015
End
January 20, 2017
Duration
1 year, 338 days
Party
Democratic
Home State
Massachusetts
Jim Mattis
Jim Mattis
No.
26
Name
Jim Mattis
Start
January 20, 2017
End
January 1, 2019
Duration
1 year, 345 days
Party
Independent
Home State
Washington
President(s)
Donald Trump(2017–2021)
Patrick M. ShanahanActing
Patrick M. ShanahanActing
No.
Name
Patrick M. ShanahanActing
Start
January 1, 2019
End
June 23, 2019
Duration
173 days
Party
Independent
Home State
Washington
Mark EsperActing
Mark EsperActing
No.
Name
Mark EsperActing
Start
June 24, 2019
End
July 15, 2019
Duration
21 days
Party
Republican
Home State
Virginia
Richard V. SpencerActing
Richard V. SpencerActing
No.
Name
Richard V. SpencerActing
Start
July 15, 2019
End
July 23, 2019
Duration
8 days
Party
Republican
Home State
Wyoming
Mark Esper
Mark Esper
No.
27
Name
Mark Esper
Start
July 23, 2019
End
November 9, 2020
Duration
1 year, 109 days
Party
Republican
Home State
Virginia
Christopher C. MillerActing
Christopher C. MillerActing
No.
Name
Christopher C. MillerActing
Start
November 9, 2020
End
January 20, 2021
Duration
72 days
Party
Republican
Home State
Iowa
David NorquistActing
David NorquistActing
No.
Name
David NorquistActing
Start
January 20, 2021
End
January 22, 2021
Duration
2 days
Party
Republican
Home State
Massachusetts
President(s)
Joe Biden(2021–2025)
Lloyd Austin
Lloyd Austin
No.
28
Name
Lloyd Austin
Start
January 22, 2021
End
January 20, 2025
Duration
3 years, 364 days
Party
Independent
Home State
Georgia
Robert G. SalessesActing
Robert G. SalessesActing
No.
Name
Robert G. SalessesActing
Start
January 20, 2025
End
January 25, 2025
Duration
5 days
Party
Independent
Home State
Rhode Island
President(s)
Donald Trump(2025–present)
Pete Hegseth
Pete Hegseth
No.
29
Name
Pete Hegseth
Start
January 25, 2025
End
Incumbent
Duration
283 days
Party
Republican
Home State
Minnesota
No.
Image
Name
Start
End
Duration
Party
Home State
President(s)
1
James Forrestal
September 17, 1947
March 28, 1949
1 year, 192 days
Democratic
New York
Harry S. Truman(1945–1953)
2
Louis A. Johnson
March 28, 1949
September 19, 1950
1 year, 175 days
Democratic
West Virginia
3
George C. Marshall
September 21, 1950
September 12, 1951
356 days
Independent
Pennsylvania
4
Robert A. Lovett
September 17, 1951
January 20, 1953
1 year, 125 days
Republican
New York
5
Charles Erwin Wilson
January 28, 1953
October 8, 1957
4 years, 253 days
Republican
Michigan
Dwight D. Eisenhower(1953–1961)
6
Neil H. McElroy
October 9, 1957
December 1, 1959
2 years, 53 days
Republican
Ohio
7
Thomas S. Gates Jr.
December 2, 1959
January 20, 1961
1 year, 49 days
Republican
Pennsylvania
8
Robert McNamara
January 21, 1961
February 29, 1968
7 years, 39 days
Republican
Michigan
John F. Kennedy(1961–1963)
Lyndon B. Johnson(1963–1969)
9
Clark Clifford
March 1, 1968
January 20, 1969
325 days
Democratic
Maryland
Lyndon B. Johnson(1963–1969)
10
Melvin Laird
January 22, 1969
January 29, 1973
4 years, 7 days
Republican
Wisconsin
Richard Nixon(1969–1974)
11
Elliot Richardson
January 30, 1973
May 24, 1973
114 days
Republican
Massachusetts
Bill ClementsActing
May 24, 1973
July 2, 1973
39 days
Republican
Texas
12
James R. Schlesinger
July 2, 1973
November 19, 1975
2 years, 140 days
Republican
Virginia
Richard Nixon(1969–1974)
Gerald Ford(1974–1977)
13
Donald Rumsfeld
November 20, 1975
January 20, 1977
1 year, 61 days
Republican
Illinois
Gerald Ford(1974–1977)
14
Harold Brown
January 20, 1977
January 20, 1981
4 years, 0 days
Democratic
California
Jimmy Carter(1977–1981)
15
Caspar Weinberger
January 21, 1981
November 23, 1987
6 years, 306 days
Republican
California
Ronald Reagan(1981–1989)
16
Frank Carlucci
November 23, 1987
January 20, 1989
1 year, 58 days
Republican
Virginia
William Howard Taft IVActing
January 20, 1989
March 21, 1989
60 days
Republican
Ohio
George H. W. Bush(1989–1993)
17
Dick Cheney
March 21, 1989
January 20, 1993
3 years, 305 days
Republican
Wyoming
18
Les Aspin
January 20, 1993
February 3, 1994
1 year, 14 days
Democratic
Wisconsin
Bill Clinton(1993–2001)
19
William Perry
February 3, 1994
January 24, 1997
2 years, 356 days
Democratic
Pennsylvania
20
William Cohen
January 24, 1997
January 20, 2001
3 years, 362 days
Republican
Maine
21
Donald Rumsfeld
January 20, 2001
December 18, 2006
5 years, 332 days(7 years, 29 days total)
Republican
Illinois
George W. Bush(2001–2009)
22
Robert Gates
December 18, 2006
June 30, 2011
4 years, 194 days
Republican
Texas
George W. Bush(2001–2009)
Barack Obama(2009–2017)
23
Leon Panetta
July 1, 2011
February 26, 2013
1 year, 240 days
Democratic
California
Barack Obama(2009–2017)
24
Chuck Hagel
February 27, 2013
February 17, 2015
1 year, 355 days
Republican
Nebraska
25
Ash Carter
February 17, 2015
January 20, 2017
1 year, 338 days
Democratic
Massachusetts
26
Jim Mattis
January 20, 2017
January 1, 2019
1 year, 345 days
Independent
Washington
Donald Trump(2017–2021)
Patrick M. ShanahanActing
January 1, 2019
June 23, 2019
173 days
Independent
Washington
Mark EsperActing
June 24, 2019
July 15, 2019
21 days
Republican
Virginia
Richard V. SpencerActing
July 15, 2019
July 23, 2019
8 days
Republican
Wyoming
27
Mark Esper
July 23, 2019
November 9, 2020
1 year, 109 days
Republican
Virginia
Christopher C. MillerActing
November 9, 2020
January 20, 2021
72 days
Republican
Iowa
David NorquistActing
January 20, 2021
January 22, 2021
2 days
Republican
Massachusetts
Joe Biden(2021–2025)
28
Lloyd Austin
January 22, 2021
January 20, 2025
3 years, 364 days
Independent
Georgia
Robert G. SalessesActing
January 20, 2025
January 25, 2025
5 days
Independent
Rhode Island
Donald Trump(2025–present)
29
Pete Hegseth
January 25, 2025
Incumbent
283 days
Republican
Minnesota
· Succession › Secretary succession
1
1
#
1
Office
Deputy Secretary of Defense
2*
2*
#
2*
Office
Secretary of the ArmySecretary of the NavySecretary of the Air Force
3
3
#
3
Office
Under Secretary of Defense for Policy
4
4
#
4
Office
Under Secretary of Defense for Intelligence and Security
-
-
#
-
Office
Chief Management Officer of the Department of Defense**
5
5
#
5
Office
Under Secretary of Defense for Acquisition and Sustainment
6
6
#
6
Office
Under Secretary of Defense for Research and Engineering
7
7
#
7
Office
Under Secretary of Defense (Comptroller)
8
8
#
8
Office
Under Secretary of Defense for Personnel and Readiness
9
9
#
9
Office
Deputy Under Secretary of Defense for Policy
10
10
#
10
Office
Deputy Under Secretary of Defense for Intelligence and Security
11
11
#
11
Office
Deputy Under Secretary of Defense for Acquisition and Sustainment
12
12
#
12
Office
Deputy Under Secretary of Defense for Research and Engineering
13
13
#
13
Office
Deputy Under Secretary of Defense (Comptroller)
14
14
#
14
Office
Deputy Under Secretary of Defense for Personnel and Readiness
15*
15*
#
15*
Office
General Counsel of the Department of DefenseAssistant Secretaries of DefenseDirector of Cost Assessment and Program EvaluationDirector of Operational Test and EvaluationChief Information Officer of the Department of Defense
16*
16*
#
16*
Office
Under Secretary of the ArmyUnder Secretary of the NavyUnder Secretary of the Air Force
17*
17*
#
17*
Office
Assistant Secretaries of the ArmyAssistant Secretaries of the NavyAssistant Secretaries of the Air ForceGeneral Counsel of the ArmyGeneral Counsel of the NavyGeneral Counsel of the Air Force
#
Office
1
Deputy Secretary of Defense
2*
Secretary of the ArmySecretary of the NavySecretary of the Air Force
3
Under Secretary of Defense for Policy
4
Under Secretary of Defense for Intelligence and Security
-
Chief Management Officer of the Department of Defense**
5
Under Secretary of Defense for Acquisition and Sustainment
6
Under Secretary of Defense for Research and Engineering
7
Under Secretary of Defense (Comptroller)
8
Under Secretary of Defense for Personnel and Readiness
9
Deputy Under Secretary of Defense for Policy
10
Deputy Under Secretary of Defense for Intelligence and Security
11
Deputy Under Secretary of Defense for Acquisition and Sustainment
12
Deputy Under Secretary of Defense for Research and Engineering
13
Deputy Under Secretary of Defense (Comptroller)
14
Deputy Under Secretary of Defense for Personnel and Readiness
15*
General Counsel of the Department of DefenseAssistant Secretaries of DefenseDirector of Cost Assessment and Program EvaluationDirector of Operational Test and EvaluationChief Information Officer of the Department of Defense
16*
Under Secretary of the ArmyUnder Secretary of the NavyUnder Secretary of the Air Force
17*
Assistant Secretaries of the ArmyAssistant Secretaries of the NavyAssistant Secretaries of the Air ForceGeneral Counsel of the ArmyGeneral Counsel of the NavyGeneral Counsel of the Air Force
Order of Succession is determined by the seniority of officials in their role.
Office dissolved on January 1, 2021.
· External links
Preceded byScott Bessentas Secretary of the Treasury
Preceded byScott Bessentas Secretary of the Treasury
U.S. order of precedence (ceremonial)
Preceded byScott Bessentas Secretary of the Treasury
U.S. order of precedence (ceremonial)
Order of precedence of the United Statesas Secretary of Defense
U.S. order of precedence (ceremonial)
Succeeded byPam Bondias Attorney General
U.S. presidential line of succession
U.S. presidential line of succession
U.S. order of precedence (ceremonial)
U.S. presidential line of succession
Preceded bySecretary of the TreasuryScott Bessent
Preceded bySecretary of the TreasuryScott Bessent
U.S. order of precedence (ceremonial)
Preceded bySecretary of the TreasuryScott Bessent
U.S. order of precedence (ceremonial)
6th in line
U.S. order of precedence (ceremonial)
Succeeded byAttorney GeneralPam Bondi
order of precedence (ceremonial)
Preceded byScott Bessentas Secretary of the Treasury
Order of precedence of the United Statesas Secretary of Defense
Succeeded byPam Bondias Attorney General
presidential line of succession
Preceded bySecretary of the TreasuryScott Bessent
6th in line
Succeeded byAttorney GeneralPam Bondi

References

  1. Executive Order 14347 authorized the usage of "Department of War" as a secondary name (which is now preferred by the dep
    https://www.federalregister.gov/documents/2025/09/10/2025-17508/restoring-the-united-states-department-of-war
  2. As only an act of Congress can legally change the name of the position, in September 2025, President Donald Trump author
    https://www.federalregister.gov/documents/2025/09/10/2025-17508/restoring-the-united-states-department-of-war
  3. According to the Executive Order precedence states – in layman's terms – that appointees designated the same succession
  4. Congress disestablished the CMO position with the passage of the William M. (Mac) Thornberry National Defense Authorizat
  5. United States Army Institute of Heraldry
    https://web.archive.org/web/20230916181026/https://tioh.army.mil/Catalog/Heraldry.aspx?HeraldryId=16096&CategoryId=9316&grp=2
  6. Senior Airman
    https://web.archive.org/web/20250920231253/https://www.dvidshub.net/image/9303753/secwar-hegseth-visits-muniz-angb
  7. "3 U.S. Code § 19 – Vacancy in offices of both President and Vice President; officers eligible to act"
    https://www.law.cornell.edu/uscode/text/3/19
  8. 5 U.S.C. § 5312
    https://www.law.cornell.edu/uscode/text/5/5312
  9. www.cbsnews.com
    https://www.cbsnews.com/news/trump-department-of-war-defense/
  10. www.nbcnews.com
    https://www.nbcnews.com/politics/donald-trump/trump-executive-order-rebranding-defense-department-war-department-rcna229217
  11. 10 U.S.C. § 113.
    https://www.law.cornell.edu/uscode/text/10/113
  12. DoDD 5100.1: Enclosure 2: a
  13. 5 U.S.C. § 101.
    https://www.law.cornell.edu/uscode/text/5/101
  14. NATO
    https://www.nato.int/cps/en/SID-C0FDE451-36F2483B/natolive/nato_countries.htm
  15. 50 U.S.C. § 402.
    https://www.law.cornell.edu/uscode/text/50/402
  16. 10 U.S.C. § 162
    https://www.law.cornell.edu/uscode/text/10/162
  17. Joint Publication 1: II-9, II-10 & II-11.
  18. 10 U.S.C. § 3011
    https://www.law.cornell.edu/uscode/text/10/3011
  19. 10 U.S.C. § 5011
    https://www.law.cornell.edu/uscode/text/10/5011
  20. 10 U.S.C. § 8011
    https://www.law.cornell.edu/uscode/text/10/8011
  21. See 10 U.S.C. § 113. The National Security Act of 1947 originally required an interval of ten years after relief from a
    https://www.law.cornell.edu/uscode/text/10/113
  22. 10 U.S.C. § 152
    https://www.law.cornell.edu/uscode/text/10/152
  23. Trask & Goldberg: pp.11 & 52
  24. Cohen: p.231.
  25. Center for American Progress
    https://www.americanprogress.org/issues/security/news/2006/10/31/2215/rumsfelds-management-failures/
  26. Cabinets and Counselors: The President and the Executive Branch (1997). Congressional Quarterly. p. 87.
  27. UNT Digital Library
    https://digital.library.unt.edu/ark:/67531/metadc958680/m1/1/
  28. NPR.org
    https://www.npr.org/2017/01/09/508902893/why-generals-need-congressional-waivers-to-become-defense-secretary
  29. The Wall Street Journal
    https://www.wsj.com/articles/lawmakers-approve-waiver-allowing-lloyd-austin-to-become-defense-chief-11611269413
  30. Department of Defense Directive 5100.01 Functions of the Department of Defense and Its Major Components
  31. DoDD 5100.1: p.1.
  32. DoDM 1348.33, Vol 3: p.39 (Enclosure 3)
  33. 50 U.S.C. § 402
    https://www.law.cornell.edu/uscode/text/50/402
  34. "Salary Table No. 2024-EX Rates of Basic Pay for the Executive Schedule (EX)"
    https://www.opm.gov/policy-data-oversight/pay-leave/salaries-wages/salary-tables/pdf/2024/EX.pdf
  35. Office of the Secretary of Defense – Historical Office
    https://history.defense.gov/Multimedia/Biographies/Article-View/Article/571293/james-v-forrestal/
  36. Office of the Secretary of Defense – Historical Office
    https://history.defense.gov/Multimedia/Biographies/Article-View/Article/571265/louis-a-johnson/
  37. Office of the Secretary of Defense – Historical Office
    https://history.defense.gov/Multimedia/Biographies/Article-View/Article/571266/george-c-marshall/
  38. Office of the Secretary of Defense – Historical Office
    https://history.defense.gov/Multimedia/Biographies/Article-View/Article/571267/robert-a-lovett/
  39. Office of the Secretary of Defense – Historical Office
    https://history.defense.gov/Multimedia/Biographies/Article-View/Article/571268/charles-e-wilson/
  40. Office of the Secretary of Defense – Historical Office
    https://history.defense.gov/Multimedia/Biographies/Article-View/Article/571269/neil-h-mcelroy/
  41. Office of the Secretary of Defense – Historical Office
    https://history.defense.gov/Multimedia/Biographies/Article-View/Article/571270/thomas-s-gates-jr/
  42. Office of the Secretary of Defense – Historical Office
    https://history.defense.gov/Multimedia/Biographies/Article-View/Article/571271/robert-s-mcnamara/
  43. Office of the Secretary of Defense – Historical Office
    https://history.defense.gov/Multimedia/Biographies/Article-View/Article/571292/clark-m-clifford/
  44. Office of the Secretary of Defense – Historical Office
    https://history.defense.gov/Multimedia/Biographies/Article-View/Article/571291/melvin-r-laird/
  45. Office of the Secretary of Defense – Historical Office
    https://history.defense.gov/Multimedia/Biographies/Article-View/Article/571290/elliot-l-richardson/
  46. Citizen Airmen: A History of the Air Force Reserve 1946–1994
    https://books.google.com/books?id=8Y3tmhPrl44C&q=William+P.+Clements,+Jr.+Acting+Secretary+of+Defense&pg=PA252
  47. Office of the Secretary of Defense – Historical Office
    https://history.defense.gov/Multimedia/Biographies/Article-View/Article/571289/james-r-schlesinger/
  48. Office of the Secretary of Defense – Historical Office
    https://history.defense.gov/Multimedia/Biographies/Article-View/Article/571288/donald-h-rumsfeld/
  49. Office of the Secretary of Defense – Historical Office
    https://history.defense.gov/Multimedia/Biographies/Article-View/Article/571287/harold-brown/
  50. Office of the Secretary of Defense – Historical Office
    https://history.defense.gov/Multimedia/Biographies/Article-View/Article/571286/caspar-w-weinberger/
  51. Office of the Secretary of Defense – Historical Office
    https://history.defense.gov/Multimedia/Biographies/Article-View/Article/571285/frank-c-carlucci/
  52. "II. Secretaries of Defense"
    https://web.archive.org/web/20170211081016/http://www.whs.mil/library/Key47-04/II.pdf
  53. Office of the Secretary of Defense – Historical Office
    https://web.archive.org/web/20190614191740/https://history.defense.gov/Multimedia/Biographies/Article-View/Article/571284/richard-b-cheney
  54. "Leslie Aspin – William J. Clinton Administration"
    https://history.defense.gov/Multimedia/Biographies/Article-View/Article/571283/leslie-aspin/
  55. Department of Defense Key Officials September 1947 – February 2019
  56. "Les Aspin Serves One Year As Defense Secretary"
    https://library.cqpress.com/cqalmanac/document.php?id=cqal93-1106289
  57. "William J. Perry – William J. Clinton Administration"
    https://web.archive.org/web/20210422203733/https://history.defense.gov/Multimedia/Biographies/Article-View/Article/571282/william-j-perry
  58. "II. Secretaries of Defense"
    https://web.archive.org/web/20170211081016/http://www.whs.mil/library/Key47-04/II.pdf
  59. "William S. Cohen – William J. Clinton Administration"
    https://history.defense.gov/Multimedia/Biographies/Article-View/Article/571281/william-s-cohen/
  60. "Donald H. Rumsfeld – George W. Bush Administration"
    https://history.defense.gov/Multimedia/Biographies/Article-View/Article/571280/donald-h-rumsfeld/
  61. "Robert M. Gates – George W. Bush / Barack Obama Administration"
    https://web.archive.org/web/20170207114027/http://history.defense.gov/Multimedia/Biographies/Article-View/Article/571279/robert-m-gates
  62. "Leon E. Panetta – Barack Obama Administration"
    https://history.defense.gov/Multimedia/Biographies/Article-View/Article/571278/leon-e-panetta/
  63. "Chuck Hagel – Barack Obama Administration"
    https://history.defense.gov/Multimedia/Biographies/Article-View/Article/571277/chuck-hagel/
  64. "Ashton B. Carter – Barack Obama Administration"
    https://web.archive.org/web/20170207195408/http://history.defense.gov/Multimedia/Biographies/Article-View/Article/571296/ashton-b-carter
  65. "James N. Mattis – Donald Trump Administration"
    https://history.defense.gov/Multimedia/Biographies/Article-View/Article/1059855/james-n-mattis/
  66. Congress.gov
    https://www.congress.gov/nomination/115th-congress/583
  67. "Dr. Mark T. Esper – Acting Secretary of Defense"
    https://www.defense.gov/About/Biographies/Biography/Article/1378166/dr-mark-t-esper/
  68. "Letter from Acting Secretary of Defense Richard V. Spencer to Pentagon"
    https://news.usni.org/2019/07/15/letter-from-acting-secretary-of-defense-richard-v-spencer-to-pentagon
  69. The Hill
    https://thehill.com/policy/defense/535078-trump-administration-official-norquist-sworn-in-as-acting-pentagon-chief
  70. cnn.com
    https://edition.cnn.com/2021/01/22/politics/lloyd-austin-senate-vote-confirmation/index.html
  71. 3 U.S.C. § 19.
    https://www.law.cornell.edu/uscode/text/3/19
  72. "Executive Order on Providing an Order of Succession within the Department of Defense"
    https://www.federalregister.gov/documents/2020/12/15/2020-27739/providing-an-order-of-succession-within-the-department-of-defense
  73. "Department of Defense Implements Section 901 of the FY2021 National Defense Authorization Act"
    https://www.defense.gov/News/Releases/Release/Article/2468186/department-of-defense-implements-section-901-of-the-fy2021-national-defense-aut/
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