Oversees the U.S. military under a civilian Secretary of Defense — by deliberate design, not incidental structure.
The Department of Defense organizes, trains, and equips the Army, Navy, Air Force, Marine Corps, and Space Force, and carries out military operations directed by the President as Commander-in-Chief.
The purpose of the Department of Defense is to provide the military forces needed to deter war and ensure our nation’s security.
Department of Defense mission statement
What It Does
The Secretary of Defense is a civilian appointee — by law, someone who has been out of active military service for a set number of years before taking the role — a structural requirement meant to preserve civilian control of the military rather than military self-governance.
Organizes the armed forces
Oversees the Army, Navy, Air Force, Marine Corps, and Space Force, plus National Guard and reserve components.
Executes operations
Carries out operations directed by the President, through the chain of command to combatant commanders.
Manages the largest federal budget
DoD’s annual budget exceeds any other federal department’s, funding personnel, equipment, research, and worldwide operations.
Supports service members
Provides pay, benefits, healthcare, and family support programs across the force.
How It Fits Into Government
The President, not the Secretary, is Commander-in-Chief
The Secretary of Defense sits in the operational chain of command between the President and combatant commanders, but the President holds ultimate command authority. Congress declares war, funds the military through annual defense appropriations and authorization acts, and confirms senior officers. The Chairman of the Joint Chiefs of Staff is the President’s principal military adviser but holds no independent operational command authority.
Major Components
Military departments
The Army, Navy, Air Force, and Space Force, each organized under its own civilian secretary.
- Department of the Army
- Department of the Navy
- Department of the Air Force
Combatant commands
Regional and functional commands that direct actual military operations worldwide.
- Regional commands
- Functional commands
Defense agencies
Specialized agencies supporting intelligence, logistics, and procurement across the department.
- Defense Intelligence Agency
- Defense Logistics Agency
How It Is Checked
Congress
Declares war, funds the military annually, and confirms senior military and civilian officers.
Courts
Military courts operate under their own system (the Uniform Code of Military Justice), with limited civilian court review.
Civilian control
A civilian Secretary of Defense and civilian service secretaries oversee the uniformed military by statutory design.
Inspector General
The DoD OIG audits programs and investigates waste, fraud, and misconduct across the department.
Public Services Visitors May Need
Check a defense contract or awardPublic contract data through USAspending.→
Find a military base or installationLocations, contact info, and visitor access requirements.→
Support resources for service members and familiesBenefits, healthcare, and family programs.→
The Joint Chiefs don’t command troops
A common misconception is that the Chairman of the Joint Chiefs of Staff, as the senior-most military officer, commands military operations. In practice, the Chairman is the President’s principal military adviser but holds no operational command authority — actual command runs from the President through the Secretary of Defense directly to combatant commanders, not through the Joint Chiefs. This separation of advisory and command roles is itself part of the same civilian-control design that requires a civilian Secretary of Defense in the first place.
