Updated January 24, 2020
Defense Primer: The Department of Defense
The Department of Defense (DOD) was established after
The Defense Agencies, sometimes called “DOD’s
World War II through the 1947 National Security Act. At
fourth estate,” which provide or manage specific
the time, some, including President Truman, took the view
capabilities for the department, such as logistics or
that the different components of the U.S. military had been
security cooperation.
insufficiently integrated to wage World War II effectively.
The intention of the 1947 Act was therefore to create, for
The Office of the Secretary of Defense (OSD)
the first time, an integrated institution that combined the
According to the DOD website, the Office of the Secretary
Departments of War and Navy, and to establish a policy
of Defense (OSD) assists the Secretary of Defense in
architecture for overseeing the newly reorganized military
several areas: policy development, planning, resource
apparatus. Over time, DOD has grown into one of the
management, fiscal management, and program evaluation.
largest bureaucracies in the world, comprising over 3
OSD also provides civilian oversight of the military
million employees stationed across the United States and
services and combatant commands to ensure that the
around the globe.
Secretary and the President’s defense objectives are met.
The Joint Chiefs of Staff (JCS)
The Joint Chiefs of Staff is the preeminent military
“One of the lessons which have most clearly come
advisory body in U.S. national security establishment. Its
from the costly and dangerous experience of this war
membership consists of the five military service chiefs
is that there must be unified direction of land, sea and
(Army, Navy, Air Force, Marine Corps and National Guard
air forces at home as well as in other parts of the
Bureau), the Chairman of the Joint Chiefs of Staff (CJCS),
world where our Armed Forces are serving. We did
and the Vice Chairman of the Joint Chiefs of Staff
not have that kind of direction when we were
(VCJCS). The JCS regularly convenes to formulate and
attacked four years ago—and we certainly paid a high
provide its best military advice to the President, the
price for not having it.”
National Security Council, the Homeland Security Council,
President Harry S. Truman, “Message to Congress,”
and the Secretary of Defense. According to Title 10, U.S.
December 19, 1945.
Code, §151, the Chairman is the principal military advisor
to the President. Chairmen therefore have statutory
responsibility to present their counsel—as well as any
dissenting views from other members of the JCS—to senior
DOD’s purpose today is to provide the President with the
leaders in the U.S. national security establishment. Of note,
military forces needed to deter war and to protect the
although the Chairman plans, coordinates, and oversees
security of the country. It does so through five primary sets
military operations involving U.S. forces, neither the
of institutions, each representing thousands of people and
Chairman nor the JCS has a formal role in the execution of
often hundreds of specific offices:
military operations—a role instead assigned to the unified
combatant commanders.
The Office of the Secretary of Defense, which helps
the Secretary plan, advise, and carry out the nation’s
The CJCS is supported by the Joint Staff, which assist in
security policies as directed by both the Secretary of
developing the unified strategic direction of the combatant
Defense and the President.
forces, their operation under unified command, and for their
integration into an efficient team of land, naval, and air
The Joint Chiefs of Staff and Joint Staff, which
forces. The “Joint Staff” is composed of approximately
collectively, through the Chairman of the Joint Chiefs of
equal numbers of officers from the Army, Navy, Marine
Staff, provides advice to the President, the National
Corps, and Air Force. In practice, the Marines make up
Security Council, the Homeland Security Council, and
about 20% of the number allocated to the Navy
the Secretary of Defense on military matters.
(http://www.jcs.mil/About/).
The Military Departments, which train and equip their
The Military Departments
personnel to perform warfighting, peacekeeping and
There are three military departments: the Army, Navy and
humanitarian/disaster assistance tasks.
Air Force. The Marine Corps, mainly an amphibious force,
is part of the Department of the Navy. DOD is also
The Unified Combatant Commands, which deploy
reportedly proposing the establishment of another military
troops and exercise military power on behalf of the
department focused on space, subject to congressional
President and the Secretary of Defense with the advice
approval. These departments are tasked with training and
of the Joint Chiefs of Staff.
equipping military forces to be utilized by the combatant
commands; departments are therefore responsible for
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Defense Primer: The Department of Defense
DOD’s “supply” of military forces and equipment. Each
psychological warfare, civil education, and insurgency
department is led by a civilian service secretary and
capabilities; and
supported by a service chief. A service chief is a senior
military officer designated as the principal military advisor
U.S. Transportation Command (USTRANSCOM),
to a departmental secretary for matters relating to a specific
which provides air, land, and sea transportation to
armed service.
different components of the Department of Defense.
In terms of overall roles and responsibilities, The Army
U.S. Cyber Command (USCYBERCOM) directs,
defends the land mass of the United States, its territories,
synchronizes, and coordinates cyberspace planning and
commonwealths, and possessions; it operates in more than
operations to defend and advance national interests in
50 countries. The Navy maintains, trains, and equips
collaboration with domestic and international partners.
combat-ready maritime forces capable of winning wars,
deterring aggression, and maintaining freedom of the seas.
U.S. Space Command (USSPACECOM), established in
The U.S. Marine Corps maintains ready expeditionary
2019, which deters aggression and conflict, defends U.S.
forces, sea-based and integrated air-ground units for
and allied freedom of action, delivers space combat
contingency and combat operations, and the means to
power for the Joint/Combined force, and develops joint
stabilize or contain international disturbance. The Air Force
warfighters to advance U.S. and allied interests in, from,
provides a rapid, flexible, and, when necessary, lethal air
and through the space domain.
and space capability that can deliver forces anywhere in the
world in less than 48 hours.
Defense Agencies
Title 10, U.S.C., §191 grants the Secretary of Defense
Unified Combatant Commands
authority to establish agencies that provide for the
The Unified Combatant Commands, or “COCOMs,” are the
performance of a supply or service activity that is common
principal mechanism through which the Department of
to more than one military department, in instances where
Defense conducts its global operations. The COCOMs
doing so is deemed more effective, economical, or efficient
represent the “demand” side of DOD, as it is primarily the
than existing structures. Organizations established under
COCOM’s operational needs that drive the development of
this authority are referred to as either Defense Agencies or a
military requirements across the department.
Department of Defense Field Activity. According to DOD’s
Chief Management Officer, there are 20 Defense Agencies
There are six regionally focused COCOMS:
(9 of which are also designated Combat Support Agencies
pursuant to Title 10, U.SC., §193, meaning that they are
U.S. Africa Command, responsible for sub-Saharan
jointly overseen by the Chairman of the Joint Chiefs of
Africa;
Staff), and 8 DOD Field Activities.
U.S. European Command, responsible for all of Europe,
DOD Reform
large portions of Central Asia, parts of the Middle East,
Managing an organization as large and complex as DOD
and the Arctic and Atlantic Oceans;
presents a unique challenge to its senior leaders. Concerns
about the department’s efficiency, effectiveness, or both
U.S. Central Command, responsible for most of the
have driven reform initiatives since the establishment of
Middle East, parts of Northern Africa and west Asia,
DOD itself. One particular tension that was built into
and part of the Indian Ocean;
Truman’s initial DOD design is that between the military
services on the one hand, which strive to protect and
U.S. Northern Command, responsible for defense of the
advance their institutional ethos and capabilities, and joint
continental United States and coordination of security
or defense-wide institutions on the other, which seek to
and military relationships with Canada and Mexico;
advance a greater degree of integration between DOD’s
constituent parts. In the early 1980s, congressional concerns
U.S. Southern Command, responsible for Central
that the services had undue—and unhelpful—influence in
America, South America, and the Caribbean; and
the conduct of military operations led to the 1986
Goldwater-Nichols Defense Reform Act. Thirty years later,
U.S. Indo-Pacific Command, responsible for the Pacific
the FY2017 National Defense Authorization Act (S. 2943)
Ocean, Southwest Asia, Australia, South Asia, and parts
also sought to reform the way DOD is organized, with the
of the Indian Ocean. It shares responsibility for Alaska
overall aim of improving the department’s agility and
with U.S. Northern Command.
strategic integration of its global assets.
There are also five “functional” COCOMs:
CRS Products
U.S. Strategic Command, which is responsible for
CRS Report R44474, Goldwater-Nichols at 30: Defense Reform
controlling space, deterring attacks on the United States
and Issues for Congress, by Kathleen J. McInnis
and its allies, launching and operating satellite systems,
and directing the use of U.S. strategic forces;
U.S. Special Operations Command, which provides
Kathleen J. McInnis, Analyst in International Security
counter-paramilitary, counter-narcotics, guerilla,
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Defense Primer: The Department of Defense
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