Updated March 13, 2024
Defense Primer: The Department of Defense
The Department of Defense (DOD) was established after
The Joint Chiefs of Staff (JCS)
World War II through the 1947 National Security Act (P.L.
The Joint Chiefs of Staff is the preeminent military
80-253). At the time, some, including President Truman,
advisory body in U.S. national military establishment. Its
took the view that the different components of the U.S.
membership consists of the six military service chiefs
military had been insufficiently integrated to wage World
(Army, Navy, Air Force, Marine Corps, National Guard
War II effectively. The intention of the 1947 Act was
Bureau, and Space Force), the Chairman of the Joint Chiefs
therefore to create, for the first time, an integrated
of Staff (CJCS), and the Vice Chairman of the Joint Chiefs
institution that combined the Departments of War and
of Staff (VCJCS). The JCS regularly convenes to formulate
Navy, and to establish a policy architecture for overseeing
and provide its best military advice to the President, the
the newly reorganized military apparatus. Over time, DOD
National Security Council, and the Secretary of Defense.
has grown into one of the largest bureaucracies in the
According to Title 10, U.S.C., §151, the Chairman is the
world, currently comprising more than 2.9 million service
principal military advisor to the President. The CJCS
members and civilians stationed in 4,686 sites across the
therefore has statutory responsibility to present his or her
United States and around the globe. Congress, in its
counsel—as well as any dissenting views from other
constitutional role, legislates both defense authorization and
members of the JCS—to senior leaders in the U.S. national
appropriations bills, and conducts oversight on DOD. The
security establishment. Per the Goldwater-Nichols
Senate confirms multiple military officers and certain DOD
Department of Defense Reorganization Act of 1986 (P.L.
civilian officials.
99-433 ),“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
“One of the lessons which have most clearly come
command.” While the CJCS is to plan, coordinate, and
from the costly and dangerous experience of this war
oversee military operations involving U.S. forces,
is that there must be unified direction of land, sea and
according to the JCS website, the JCS “have no executive
air forces at home as well as in other parts of the
authority to command combatant forces.”
world where our Armed Forces are serving. We did
not have that kind of direction when we were
The CJCS is supported by the Joint Staff, which assists in
attacked four years ago—and we certainly paid a high
developing the unified strategic direction of the combatant
price for not having it.”
forces, their operation under unified command, and their

integration into an efficient team of land, naval, and air
President Harry S. Truman, “Message to Congress,”
forces. The Joint Staff is composed of officers and
December 19, 1945.
noncommissioned officers from the Army, Navy, Marine
Corps, Air Force, and Space Force, as well as Department
DOD’s
of Defense civilians.
mission today is “to provide the military forces
needed to deter war and ensure our nation’s security.” It
The Military Departments
does so through five primary sets of institutions, each
There are three military departments: the Army, Navy and
representing thousands of people and often hundreds of
Air Force. The Marine Corps, mainly an amphibious force,
specific offices.
is part of the Department of the Navy. The Space Force is
• The Office of the Secretary of Defense.
part of the Department of the Air Force. The departments
•
organize, train, and equip the military forces utilized by the
The Joint Chiefs of Staff and Joint Staff.
combatant commands. According to Title 10, U.S. Code,
• The Military Departments.
Sections 7013, 8013, and 9013, each department is led by a
•
civilian service secretary who “is responsible for, and has
The Unified Combatant Commands.
the authority necessary to conduct, all affairs of the
• The Defense Agencies.
Department.” Each service has a service chief (a senior
military officer in the grade of O-10, General or Admiral)
The Office of the Secretary of Defense (OSD)
who performs his or her duties under the authority,
Title 10 U.S. Code Section 113 specifies that the Secretary
direction, and control of the department’s secretary and is
of Defense exercises “authority, direction and control” over
directly responsible to the Secretary.
DOD. The Office of the Secretary of Defense (OSD) assists
the Secretary in exercising such authority in a variety of
In terms of roles and responsibilities, the Army trains and
areas, including policy development, planning, resource
equips forces to provide ready, prompt, and sustained land
management, fiscal management, and program evaluation.
dominance across the full spectrum of conflict as part of the
OSD also helps provide civilian oversight of the military
joint force. The Navy trains, and equips combat-ready
services and combatant commands.
maritime forces capable of winning wars, deterring
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Defense Primer: The Department of Defense
aggression, and maintaining freedom of the seas. The U.S.
Defense Agencies
Marine Corps maintains ready expeditionary forces, sea-
Title 10, U.S.C. §191, grants the Secretary of Defense
based and integrated air-ground units for contingency and
authority to establish agencies that provide for the
combat operations. The Air Force provides a rapid, flexible,
performance of a supply or service activity that is common
and, when necessary, lethal air capability that can deliver
to more than one military department when doing so is
forces anywhere in the world. The Space Force organizes,
deemed more effective, economical, or efficient than
trains, and equips its forces for global space operations.
existing structures. DOD refers to any organization
established under this authority as either a Defense Agency
Unified Combatant Commands
or a DOD Field Activity. According to DOD’s FY2023
The Unified Combatant Commands, or “COCOMs,” are the
Agency Financial Report, there are 19 Defense Agencies
principal mechanism through which DOD conducts its
and eight DOD Field Activities. Eight of the Defense
global operations. It is primarily the COCOMs’ operational
Agencies are also designated Combat Support Agencies
needs that drive the development of military requirements
pursuant to 10 U.S.C. §193. While these agencies’ chains of
across the department.
command do not include the CJCS, such a designation
requires that the CJCS report at least biannually to the
There are seven regionally focused COCOMs.
Secretary of Defense and the congressional defense
•
committees on the ability of each agency to support
U.S. Africa Command (AFRICOM), responsible for
operating forces in time of war or threat to national
sub-Saharan Africa.
security. The Combat Support Agencies are the Defense
• U.S. European Command (EUCOM), responsible for all
Information Systems Agency, Defense Contract
of Europe, large portions of Central Asia, parts of the
Management Agency, Defense Logistics Agency, Defense
Middle East, and the Arctic and Atlantic Oceans.
Threat Reduction Agency, Defense Health Agency,
•
Defense Intelligence Agency, National Geospatial-
U.S. Central Command (CENTCOM), responsible for
Intelligence Agency, and the National Security Agency/
most of the Middle East, parts of Northern Africa and
Central Security Service.
west Asia, and part of the Indian Ocean.
• U.S. Northern Command, (NORTHCOM) responsible
DOD Reform
for defense of the continental United States and
Managing an organization as large and complex as DOD
coordination of security and military relationships with
presents a unique challenge to its senior leaders. Concerns
Canada and Mexico.
about the department’s efficiency, effectiveness, or both
•
have driven reform initiatives since the establishment of
U.S. Southern Command (SOUTHCOM), responsible
DOD itself. In the early 1980s, congressional concerns that
for Central America, South America, and the Caribbean.
the services had retained and exerted undue influence in the
• U.S. Indo-Pacific Command (INDOPACOM),
conduct of military operations led to the 1986 Goldwater-
responsible for the Pacific Ocean, Southwest Asia,
Nichols Defense Reform Act. Thirty years later, the
Australia, South Asia, and parts of the Indian Ocean. It
FY2017 National Defense Authorization Act (P.L. 114-
shares responsibility for Alaska with U.S. Northern
328) also sought to reform the way DOD is organized, with
Command.
the overall aim of improving the department’s agility and
strategic integration of its global assets. Congress, in its
• U.S. Space Command (SPACECOM) provides space
oversight and legislative roles, may choose to exercise its
combat power for the Joint/Combined force and
power under Article I, Section 8, Clause 1, of the
develops joint warfighters in, from, and through the
Constitution to play its reserved role in ongoing policy
space domain.
debates about DOD reform.
There are also four “functional” COCOMs.
CRS Products
• U.S. Strategic Command (STRATCOM), responsible
CRS Report R44757, Defense Primer: A Guide for New Members,
for deterring attacks on the United States and its allies
by Bryce H. P. Mendez and Lawrence Kapp
and directing the use of U.S. strategic forces.
CRS In Focus IF10542, Defense Primer: Commanding U.S.
• U.S. Special Operations Command (SOCOM) develops
Military Operations, coordinated by Nathan J. Lucas
and employs fully capable Special Operations Forces to
conduct global special operations and activities as part
of the Joint Force to support persistent, networked and
Note: This In Focus was originally written by Kathleen J.
distributed Combatant Command operations and
McInnis, former CRS Specialist in International Security.
campaigns against state and nonstate actors.
Michael J. Vassalotti, Coordinator, Section Research
• U.S. Transportation Command (TRANSCOM) provides
Manager
air, land, and sea transportation to different components
Ilana Krill, Research Assistant
of DOD.
IF10543
• U.S. Cyber Command (CYBERCOM) directs,
synchronizes, and coordinates cyberspace planning and
operations to defend and advance national interests in
collaboration with domestic and international partners.
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Defense Primer: The Department of Defense


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https://crsreports.congress.gov | IF10543 · VERSION 10 · UPDATED

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