The Secretary of Defense is the civilian head of the U.S. Department of Defense, the President’s principal advisor on defense matters, and the person who holds legal authority, direction, and control over the entire military establishment — more than two million active-duty service members, over 800,000 National Guard and Reserve members, and roughly 770,000 civilian employees. The position is a Cabinet post, sits sixth in the presidential line of succession, and links the President to the commanders who actually run military operations around the world.
In September 2025, the department was officially renamed the Department of War and the officeholder’s title changed accordingly. The statutory authorities described here, all rooted in Title 10 of the United States Code, remain in place.
The Statutory Role
The office was created by the National Security Act of 1947, which merged the previously separate Army and Navy departments under a single defense head and established a new Department of the Air Force alongside them.1Office of the Historian. National Security Act of 1947 A 1949 amendment strengthened the Secretary’s authority over the individual services and gave the organization its Department of Defense name.
Today, 10 U.S.C. § 113 designates the Secretary as the head of the Department of Defense, the principal assistant to the President in all defense matters, and the official with authority, direction, and control over the department.2Office of the Law Revision Counsel. 10 USC 113 – Secretary of Defense The Goldwater-Nichols Act of 1986 reinforced that authority, clarifying the chain of command and strengthening civilian oversight of military operations.3U.S. Department of Defense History. Goldwater-Nichols DOD Reorganization Act of 1986
In the presidential line of succession, the Secretary ranks sixth, behind the Vice President, Speaker of the House, President Pro Tempore of the Senate, Secretary of State, and Secretary of the Treasury.4USAGov. Order of Presidential Succession
Why the Job Must Go to a Civilian
The office is designed around the principle that a civilian, not a military officer, should run the armed forces. Federal law enforces this through a cooling-off period. A person who served on active duty as a commissioned officer below O-7 (brigadier general or rear admiral lower half) cannot be appointed until at least seven years after leaving active duty. For officers who served at O-7 or above, the wait is ten years. The statute also requires that the appointee come “from civilian life,” meaning no active military status at the time of appointment.2Office of the Law Revision Counsel. 10 USC 113 – Secretary of Defense
Congress can waive these rules with special legislation, but it has done so only three times. The first waiver went to General George C. Marshall in 1950 so he could serve during the Korean War.5U.S. Government Publishing Office. House Report 115-13 – To Provide for an Exception to a Limitation Against Appointment of Persons as Secretary of Defense Within Seven Years of Relief From Active Duty The next was for retired Marine General James Mattis in 2017, and the third for retired Army General Lloyd Austin in 2021. Each required standalone legislation through both chambers, and each drew debate over whether repeated exceptions weaken the civilian control norm.
How the Secretary Is Appointed and Removed
The President nominates a candidate under Article II, Section 2 of the Constitution, which requires the advice and consent of the Senate for principal officers.6Congress.gov. Article II Section 2 Clause 2 The Senate Armed Services Committee then holds confirmation hearings covering defense policy, strategic priorities, management approach, and personal background. The committee votes on whether to recommend the nominee, and the full Senate confirms or rejects by a simple majority of those present.
Removal is far simpler. The President can dismiss the Secretary at will, without congressional approval. The Supreme Court established the President’s broad removal authority over Senate-confirmed executive officials in Myers v. United States (1926).
When the Secretary dies, resigns, or otherwise cannot serve, the Deputy Secretary of Defense automatically assumes the office’s full powers. Federal law requires the Deputy to notify the Armed Services and Appropriations committees of both chambers, along with congressional leadership, within 24 hours of any unplanned transfer. Planned transfers require the same notification at least 24 hours in advance.7Office of the Law Revision Counsel. 10 USC 132 – Deputy Secretary of Defense
Policy, Strategy, and the Budget
The Secretary is a statutory member of the National Security Council, the body that coordinates defense policy with foreign policy and other national security matters.8Office of the Law Revision Counsel. 50 USC 3021 – National Security Council That seat ensures defense considerations feed into broader presidential decisions rather than operating separately.
Every four years, the Secretary’s office produces the National Defense Strategy, a public document that describes how the department reads the global security environment, allocates forces, and prioritizes threats.9U.S. Department of Defense History. National Defense Strategy That strategy shapes the National Military Strategy, drives force structure decisions across the service branches, and guides the department’s budget submissions to Congress.
Those budgets are large. For fiscal year 2026, national defense discretionary spending exceeded $1 trillion. The Secretary runs the internal process, called Planning, Programming, Budgeting, and Execution, that divides this money across weapons programs, readiness, personnel, and research. A great deal of the office’s practical power lives in that process. A program that doesn’t survive it doesn’t get built, no matter how strongly a service chief advocates for it.
Where the Secretary Sits in the Chain of Command
Military orders flow from the President to the Secretary of Defense and then directly to the commanders of the combatant commands.10Office of the Law Revision Counsel. 10 USC 162 – Combatant Commands: Assigned Forces; Chain of Command Those commands are the operational organizations that fight wars and conduct missions: U.S. Central Command, U.S. Indo-Pacific Command, U.S. European Command, and the others. Their commanders answer directly to the President and the Secretary for assigned missions.
One point catches people off guard. The Chairman of the Joint Chiefs of Staff is the highest-ranking military officer in the country and serves as the principal military advisor to the President, the NSC, and the Secretary, but the Chairman is not in the chain of command.11Office of the Law Revision Counsel. 10 USC 151 – Joint Chiefs of Staff: Composition; Functions The Chairman advises and transmits orders but does not command combat forces. The separation is deliberate. It keeps military advice independent from the legal authority to direct troops.
Role in a Nuclear Decision
If early-warning systems detect a possible attack or unusual event, the Secretary joins an emergency conference with the President and senior military leaders, providing a threat assessment and walking through response options.12Congressional Research Service. Authority to Launch Nuclear Forces The President holds sole authority to authorize a nuclear launch. Concurrence from the Secretary, the Chairman, or Congress is not legally required. What makes the Secretary central is the chain of command: a launch order must travel through the Secretary to reach the combatant commanders whose forces would carry it out.
On stockpile management, the Department of Defense and the Department of Energy share responsibility for the safety and reliability of U.S. nuclear weapons. A Nuclear Weapons Council of senior defense and energy officials oversees warhead development, production, surveillance, and retirement.13Office of the Law Revision Counsel. 10 USC 179 – Nuclear Weapons Council The Secretary of Defense and the Secretary of Energy jointly advise the President on the annual certification that the stockpile remains safe and reliable without testing.
Authority Over the National Guard
In peacetime, National Guard units serve under their state governors. Federal law lets the President federalize Guard forces, transferring them from state control to the federal chain of command, in three circumstances: an invasion or threat of invasion, a rebellion or threat of rebellion, or when regular federal forces are insufficient to execute federal law.14Office of the Law Revision Counsel. 10 USC 12406 – National Guard in Federal Service: Call
Once federalized, Guard units run under the same chain as active-duty forces: President to Secretary to combatant commander. A middle option called Title 32 status lets Guard members perform federal missions on federal pay while staying under state command. Which status applies determines who gives the orders and under what legal authority troops operate, and it matters most in domestic emergencies where state and federal interests may diverge.
Restrictions After Leaving Office
A former Secretary faces federal limits on lobbying. Under 18 U.S.C. § 207, senior executive branch officials are generally barred for one year from making lobbying contacts with the agency where they served.15Office of the Law Revision Counsel. 18 USC 207 – Restrictions on Former Officers, Employees, and Elected Officials of the Executive and Legislative Branches Defense-specific provisions added through the National Defense Authorization Act extend that cooling-off period and broaden it to cover the entire Department of Defense rather than only the former official’s immediate office.