Defense Primer: The Department of Defense

The Department of Defense (DOD) was established after World War II by the 1947 National Security Act (P.L. 80-253). At the time, some, including President Truman, took the view that the different components of the U.S. military had been insufficiently integrated to wage World War II effectively. Congress's intent was to, inter alia, "provide a Department of Defense ... under the direction, authority, and control of the Secretary of Defense... provide more effective, efficient, and economical administration ... and provide for the unified strategic direction of the combatant forces." Over time, DOD has grown into one of the largest bureaucracies in the world, currently comprising more than 2.8 million servicemembers and civilians stationed in over 4,600 sites across the United States and around the globe. Congress, in its constitutional role, legislates both defense authorization and appropriations bills, and conducts oversight of DOD, through annual budget and posture hearings. The Senate confirms multiple military officers and DOD civilian officials, including the Secretary and Deputy Secretary, and the Chairman of the Joint Chiefs of Staff.

"One of the lessons which have most clearly come from the costly and dangerous experience of this war is that there must be unified direction of land, sea and air forces at home as well as in other parts of the world where our Armed Forces are serving. We did not have that kind of direction when we were attacked four years ago—and we certainly paid a high price for not having it."

President Harry S. Truman, "Message to Congress," December 19, 1945.

DOD's mission today is "to provide the military forces needed to deter war and ensure our nation's security." It does so through five primary sets of institutions, each representing thousands of people and often hundreds of specific offices.

• The Office of the Secretary of Defense.
• The Joint Chiefs of Staff and Joint Staff.
• The Military Departments.
• The Unified Combatant Commands.
• The Defense Agencies.

The Office of the Secretary of Defense (OSD)

Title 10, Section 113, of the U.S. Code specifies that the Secretary of Defense exercises "authority, direction and control" over DOD. The Office of the Secretary of Defense (OSD) assists the Secretary in exercising such authority in a variety of areas, including policy development, planning, resource management, fiscal management, and program evaluation. OSD political appointees and civilian employees also help provide civilian oversight of the military services and combatant commands.

The Joint Chiefs of Staff (JCS)

The Joint Chiefs of Staff is the preeminent military advisory body in the U.S. national military establishment. Its membership consists of the six military service chiefs (Army, Navy, Air Force, Marine Corps, National Guard Bureau, and Space Force), the Chairman of the Joint Chiefs of Staff (CJCS), and the Vice Chairman of the Joint Chiefs of Staff (VCJCS). The JCS regularly convenes to formulate and provide its best military advice to the President, the National Security Council, and the Secretary of Defense.

According to Title 10, Section 151, of the U.S. Code, the CJCS is the principal military advisor to the President; the CJCS does not exercise command authority over U.S. military forces. The CJCS therefore has statutory responsibility to present his or her counsel—as well as any dissenting views from other members of the JCS—to senior leaders in the U.S. national security establishment. Per the Joint Staff website, the JCS have no executive authority to command. The Goldwater-Nichols Department of Defense Reorganization Act of 1986 (P.L. 99-433 ) states, "The chain of command runs from the President to the Secretary of Defense; and from the Secretary of Defense to the commander of the combatant command."

The Joint Staff supports the CJCS by developing the unified strategic direction of the combatant forces, their operations under unified command, and their integration into an efficient team of land, naval, and air forces. The Joint Staff is composed of officers and noncommissioned officers from all five Services as well as Department of Defense civilians.

The Military Departments

There are three military departments: the Army, Navy and Air Force. The Marine Corps, mainly an amphibious force, is part of the Department of the Navy. The Space Force is part of the Department of the Air Force. The departments organize, train, and equip the military forces utilized by the combatant commands. According to Title 10, Sections 7013, 8013, and 9013, of the U.S. Code, each department is led by a civilian service secretary who "is responsible for, and has the authority necessary to conduct, all affairs of the Department." Each service has a service chief (a senior military officer in the grade of O-10, General or Admiral) who performs his or her duties under the authority, direction, and control of the department's secretary and is directly responsible to the Secretary.

In terms of roles and responsibilities, the Services are to staff, train, and equip units for combatant command operations worldwide in each combat domain. The Army is to provide forces for the land domain. The Navy is to provide forces for operations at sea. The Marine Corps is to provide expeditionary, sea-based, integrated air-ground units on land and at sea. The Air Force is to provide forces for aerial combat. The Space Force is to provide forces and integrate space operations into combatant commands' joint operations.

Unified Combatant Commands

The Unified Combatant Commands, or "COCOMs," are the principal mechanism through which DOD conducts its global operations. It is primarily the COCOMs' operational needs that drive the development of military requirements across the department.

There are seven regionally focused COCOMs.

• U.S. Africa Command (AFRICOM), responsible for sub-Saharan Africa.
• U.S. European Command (EUCOM), responsible for all of Europe, large portions of Central Asia, parts of the Middle East, and the Arctic and Atlantic Oceans.
• U.S. Central Command (CENTCOM), responsible for most of the Middle East, parts of Northern Africa and west Asia, and part of the Indian Ocean.
• U.S. Northern Command, (NORTHCOM) responsible for defense of the continental United States and coordination of security and military relationships with Canada and Mexico.
• U.S. Southern Command (SOUTHCOM), responsible for Central America, South America, and the Caribbean.
• U.S. Indo-Pacific Command (INDOPACOM), responsible for the Pacific Ocean, Southwest Asia, Australia, South Asia, and parts of the Indian Ocean. It shares responsibility for Alaska with U.S. Northern Command.
• U.S. Space Command (SPACECOM) employs joint forces and integrates them into multi-domain global operations.

There are also four "functional" COCOMs.

• U.S. Strategic Command (STRATCOM), responsible for deterring attacks on the United States and its allies and directing the use of U.S. strategic forces.
• U.S. Special Operations Command (SOCOM), responsible for developing and employing Special Operations Forces to conduct global special operations and activities as part of the Joint Force to support persistent, networked and distributed Combatant Command operations and campaigns against state and nonstate actors.
• U.S. Transportation Command (TRANSCOM), responsible for providing air, land, and sea transportation to different components of DOD.
• U.S. Cyber Command (CYBERCOM), responsible for directing, synchronizing, and coordinating cyberspace planning and operations to defend and advance national interests in collaboration with domestic and international partners.

Defense Agencies

Title 10, Section 191, of the U.S. Code grants the Secretary of Defense authority to establish agencies that provide for the performance of a supply or service activity that is common to more than one military department when the Secretary deems it more effective, economical, or efficient than existing methods, to do so. DOD refers to any organization established under this authority as either a Defense Agency or a DOD Field Activity. According to DOD's FY2024 Agency Financial Report, there are 19 Defense Agencies and eight DOD Field Activities. Eight of the Defense Agencies are also designated Combat Support Agencies pursuant to Title 10, Section 193, of the U.S. Code. While these agencies' chains of command do not include the CJCS, such a designation requires that the CJCS report at least biannually to the Secretary of Defense and the congressional defense committees on the ability of each agency to support operating forces in time of war or threat to national security. The Combat Support Agencies are the Defense Information Systems Agency, Defense Contract Management Agency, Defense Logistics Agency, Defense Threat Reduction Agency, Defense Health Agency, Defense Intelligence Agency, National Geospatial-Intelligence Agency, and the National Security Agency/ Central Security Service.

Issue for Congress – DOD Management Reform

Section 902 of the Servicemember Quality of Life Improvement and National Defense Authorization Act for Fiscal Year 2025 (H.R. 8070) created a Performance Improvement Officer (PIP) of the Department of Defense who is responsible for, inter alia, "[o]versight of transformational business modernization and business process re-engineering of the Department of Defense." The PIP is to have specific duties and responsibilities in alignment with the of the Government Performance and Results Act (GPRA) Modernization Act of 2010 (P.L. 111-352). Congress may choose to oversee implementation of the PIP role and its effect on DOD business process management, including the next DOD audit.

Note: Former CRS Specialist Kathleen J. McInnis originally wrote this In Focus. Ilana Krill, former CRS Intern, provided research and analysis for this In Focus.