The Secretary of Defense is the civilian Cabinet official who runs the United States Department of Defense, oversees all branches of the armed forces, and sits sixth in the presidential line of succession. The position was created by the National Security Act of 1947 to place a single civilian in charge of the military, reporting directly to the President.1Office of the Historian. National Security Act of 1947 In September 2025, the department was officially renamed the Department of War and the title changed to Secretary of War, though the underlying statutory authority is unchanged.2U.S. Department of War. Secretary of War Pete Hegseth, confirmed on January 24, 2025, is the 29th person to hold the office.3Congress.gov. PN11-7 – Nomination of Peter Hegseth for Department of Defense
Who Can Hold the Job
Federal law requires that the Secretary be appointed “from civilian life.” A nominee cannot hold an active military commission at the time of appointment, and the statute imposes a two-tiered cooling-off period after active service. A former commissioned officer below the rank of brigadier general (O-7) must wait at least seven years. A former officer at O-7 or above must wait at least ten.4Office of the Law Revision Counsel. 10 USC 113 – Secretary of Defense The point of the rule is civilian control of the military.
Congress can waive the cooling-off period by passing standalone legislation for a specific nominee. It has done so only three times: for George Marshall in 1950, James Mattis in 2017, and Lloyd Austin in 2021. Each waiver drew significant debate about the civilian-control principle.
Appointment follows the standard constitutional path. The President nominates, the Senate holds a confirmation hearing, and a simple majority confirms.5United States Senate. Advice and Consent: Nominations These votes can be close. Hegseth was confirmed 51–50, with the Vice President breaking the tie.3Congress.gov. PN11-7 – Nomination of Peter Hegseth for Department of Defense
What the Secretary Does
Statute defines the Secretary as “the principal assistant to the President in all matters relating to the Department of Defense.” The Secretary exercises authority, direction, and control over the entire department, including the Army, Navy, and Air Force, each of which has its own civilian secretary reporting up to the Secretary of Defense.4Office of the Law Revision Counsel. 10 USC 113 – Secretary of Defense The job covers national defense strategy, policy across the branches, and the department’s voice in interagency decisions.
The budget makes this one of the largest management jobs in government. The FY2025 National Defense Authorization Act authorized roughly $884 billion in total national defense spending, with about $850 billion going directly to the Department of Defense.6Congress.gov. FY2025 NDAA: Summary of Funding Authorizations That money pays for troop salaries and health care, research, weapons procurement, and installations worldwide. Allocation decisions shape military capability for decades.
Several major intelligence agencies also sit under the Secretary’s authority: the Defense Intelligence Agency, the National Security Agency, the National Geospatial-Intelligence Agency, and the National Reconnaissance Office.7Defense Intelligence Agency. About DIA The Secretary coordinates with the Director of National Intelligence on the wider intelligence community but retains direct control over these defense agencies.
The Secretary holds a permanent statutory seat on the National Security Council alongside the President, Vice President, and the Secretaries of State, Energy, and the Treasury.8Office of the Law Revision Counsel. 50 USC 3021 – National Security Council That seat puts defense considerations into every major national security decision the Council takes up.
Where the Secretary Sits in the Chain of Command
For military operations, the chain of command runs from the President to the Secretary of Defense, and from the Secretary to the commanders of the unified combatant commands. Federal law states this directly, and it means no general or admiral stands between the Secretary and the President operationally.9Office of the Law Revision Counsel. 10 USC 162 – Combatant Commands: Assigned Forces; Chain of Command Combatant commanders, who lead geographic and functional commands such as U.S. Indo-Pacific Command or U.S. Cyber Command, answer to the Secretary for the readiness and performance of their forces.10Office of the Law Revision Counsel. 10 USC 164 – Commanders of Combatant Commands: Assignment; Powers and Duties The military departments recruit, train, and equip; the combatant commands fight. The Secretary assigns forces from the departments to the commands, and any transfer between commands requires the Secretary’s authorization.
The Joint Chiefs
The Chairman of the Joint Chiefs is the principal military adviser to the President and the Secretary. The other service chiefs serve as additional advisers.11Office of the Law Revision Counsel. 10 USC 151 – Joint Chiefs of Staff: Composition; Functions The Chairman’s statutory functions, from strategic planning to advice on force allocation, are all performed “subject to the authority, direction, and control of the President and the Secretary of Defense.”12Office of the Law Revision Counsel. 10 USC 153 – Chairman: Functions The Joint Chiefs have no operational command authority, and the Joint Staff is prohibited by statute from functioning as an overall armed forces general staff.13Joint Chiefs of Staff. About the Joint Chiefs of Staff Career military leaders provide analysis; the civilian Secretary makes the call.
Nuclear Orders
The Secretary has a specific role in nuclear launch orders. When the President orders the use of nuclear weapons, the Secretary verifies that the order is authentic and transmits it through the chain of command. This authentication step is not a veto. The Secretary confirms the President’s identity and the legitimacy of the order but cannot override the decision.
What Happens if the Secretary Can’t Serve
If the Secretary dies, resigns, or becomes unable to serve, the Deputy Secretary of Defense assumes the full powers of the office. The Deputy is also appointed from civilian life, confirmed by the Senate, and subject to the seven-year cooling-off period from active military service.14Office of the Law Revision Counsel. 10 USC 132 – Deputy Secretary of Defense
Beyond the Deputy, Executive Order 13533 sets a deeper succession list running through the Secretaries of the Army, Navy, and Air Force and then a series of under secretaries and senior civilians. Anyone serving in an acting capacity is excluded, and each successor must have been Senate-confirmed. The President can depart from this order at any time.
At the national level, the Secretary of Defense stands sixth in the presidential line of succession, after the Vice President, Speaker of the House, President Pro Tempore of the Senate, Secretary of State, and Secretary of the Treasury.15Office of the Law Revision Counsel. 3 USC 19 – Vacancy in Offices of Both President and Vice President That placement reflects both the seniority of the office and its role in continuity of government.