United States. Department of Defense

The Pentagon is the headquarters building of the United States Department of Defense. As a symbol of the U.S. military, the phrase The Pentagon is also often used as a metonym for the Department of Defense and its leadership.

Located in Arlington County, Virginia, across the Potomac River from Washington, D.C., the building was designed by American architect George Bergstrom and built by contractor John McShain. Ground was broken on 11 September 1941, and the building was dedicated on 15 January 1943. General Brehon Somervell provided the major motivating power behind the project;[5] Colonel Leslie Groves was responsible for overseeing the project for the U.S. Army.

The Pentagon is the world's largest office building, with about 6,500,000 sq ft (600,000 m2) of space, of which 3,700,000 sq ft (340,000 m2) are used as offices.[6][7] Some 23,000 military and civilian employees,[7] and another 3,000 non-defense support personnel, work in the Pentagon. It has five sides, five floors above ground, two basement levels, and five ring corridors per floor with a total of 17.5 mi (28.2 km)[7] of corridors. The central five-acre (20,000 m2) pentagonal plaza is nicknamed "ground zero" on the presumption that it would be a prime target in a nuclear war.[8]

On 11 September 2001, exactly 60 years after the building's construction began, American Airlines Flight 77 was hijacked and flown into the western side of the building, killing 189 people (59 victims and the five terrorists on board the airliner, as well as 125 victims in the building), according to the 9/11 Commission Report.[9] It was the first significant foreign attack on Washington's governmental facilities since the city was burned by the British during the War of 1812.

The Pentagon is listed on the National Register of Historic Places and is a National Historic Landmark.[3]

The United States Department of Defense (DoD,[5] USDOD or DOD) is an executive branch department of the federal government charged with coordinating and supervising all agencies and functions of the government directly related to national security and the United States Armed Forces. The DoD is the largest employer in the world,[6] with nearly 1.3 million active-duty service members (soldiers, marines, sailors and airmen) as of 2016.[7] More employees include over 826,000 National Guard and reservists from the armed forces, and over 732,000 civilians[8] bringing the total to over 2.8 million employees.[2] Headquartered at the Pentagon in Arlington, Virginia, just outside Washington, D.C., the DoD's stated mission is to provide "the military forces needed to deter war and ensure our nation's security".[9][10]

The Department of Defense is headed by the secretary of defense, a cabinet-level head who reports directly to the president of the United States. Beneath the Department of Defense are three subordinate military departments: the Department of the Army, the Department of the Navy, and the Department of the Air Force. In addition, four national intelligence services are subordinate to the Department of Defense: the Defense Intelligence Agency (DIA), the National Security Agency (NSA), the National Geospatial-Intelligence Agency (NGA), and the National Reconnaissance Office (NRO). Other Defense agencies include the Defense Advanced Research Projects Agency (DARPA), the Strategic Capabilities Office (SCO), the Defense Logistics Agency (DLA), the Missile Defense Agency (MDA), the Defense Health Agency (DHA), Defense Threat Reduction Agency (DTRA), the Defense Counterintelligence and Security Agency (formerly the DSS), and the Pentagon Force Protection Agency (PFPA), all of which are subordinate to the secretary of defense. Additionally, the Defense Contract Management Agency (DCMA) is responsible for administering contracts for the DoD. Military operations are managed by eleven regional or functional Unified combatant commands. The Department of Defense also operates several joint services schools, including the Eisenhower School (ES) and the National War College (NWC).

U.S. Department of Defense, executive division of the U.S. federal government responsible for ensuring national security and supervising U.S. military forces. Based in the Pentagon, it includes the Joint Chiefs of Staff, the departments of the U.S. Army, U.S. Navy, and U.S. Air Force, and numerous defense agencies and allied services. It was formed in 1947 by an act of Congress (amended 1949) combining the War and Navy Departments.

The mission of the Department of Defense is to provide, through its military strength, a solid foundation for the national policy of the United States. The forerunner of the Department of Defense, the National Military Establishment, was created by the National Security Act of 1947 and evolved from the experiences of World War II. While combat and service components of the Departments of the Army and the Navy fought together in various theatres of operation under unified direction of overseas commanders, the individual military departments reported separately to the president. The conflicting and competitive policies of these departments prevented a truly effective, coordinated, and unified military effort. To overcome this organizational deficiency, the National Military Establishment was created, and the cabinet post of secretary of defense was established to provide overall policy and direction of the military departments without destroying their individual identities. Concurrently, the Air Force was created as a third military department on a coequal basis with the Departments of the Army and the Navy.

The original National Security Act of 1947 provided the secretary of defense with limited authority and staff to exercise control. However, subsequent amendments to the basic act in 1949, 1953, and 1958 greatly strengthened the authority and ability of the secretary to direct defense policy. With the 1949 amendment, the modern Department of Defense was established. In the early 21st century the Department of Defense consisted of the secretary of defense; the deputy secretary of defense; undersecretaries and assistant secretaries holding various portfolios; the office of the inspector general; the Departments of the Army, Navy, and Air Force; and numerous defense agencies and field activity offices. These civilian officials and their subordinates represent the policy, research, analysis, and resource-management staff of the secretary of defense.

The civilian secretaries of the military departments (Army, Navy, and Air Force) are responsible for the administration of their particular departments and are responsible for training, equipping, and providing combat-ready forces to the combat commands. The combat forces of the Army, Navy, Air Force, and Marine Corps are under unified combat commands, organized on either a geographic or a functional basis. A unified command contains combat forces from more than one service, such as Central Command (CENTCOM), which is composed of all Army, Navy, Air Force, and Marine Corps units in Central and Southern Asia and the Middle East, or Special Operations Command (USSOCOM), which oversees special operations warfare.

Gen. Tommy Franks (left), commander in chief of Central Command, with U.S. Secretary of Defense Donald Rumsfeld, 2002.
Gen. Tommy Franks (left), commander in chief of Central Command, with U.S. Secretary of Defense Donald Rumsfeld, 2002.
Robert D. Ward—U.S. Department of Defense
Britannica Premium: Serving the evolving needs of knowledge seekers. Get 30% your subscription today.
Subscribe Now
The commanders of the unified commands are responsible to the president and the secretary of defense. By secretarial delegation, the Joint Chiefs of Staff exercise operational direction over the unified commands. The Joint Chiefs of Staff are the principal military advisers to the president, the National Security Council, and the secretary of defense. The Joint Chiefs of Staff consist of the chairman, Joint Chiefs of Staff, who is the nation’s highest-ranking military officer; the vice chairman; the chief of staff, United States Army; the chief of naval operations; the chief of staff, U.S. Air Force; the commandant of the Marine Corps; and the chief of the National Guard. The chiefs are appointed by the president to four-year terms. The Joint Chiefs of Staff are supported by the Joint Staff, which is limited by law to not more than 400 officers. This staff is organized along conventional military staff lines, and performs such functions as developing strategic concepts and war plans, reviewing the operating plans of the unified commands, and establishing unified doctrine for operations. An assignment to the Joint Staff provides military officers a unique opportunity to work on coordinated plans and to develop an understanding of the integrated effort required under the modern concept of joint operations.

Joint Chiefs of Staff
Joint Chiefs of Staff
Pres. Barack Obama (his back to the camera) holding a meeting with the Joint Chiefs of Staff in the Oval Office concerning the repeal of "Don't Ask, Don't Tell," November 29, 2010.
Pete Souza—Official White House Photo

In the early 21st century there were 20 defense agencies within the Department of Defense. These agencies were established to provide integrated and unified effort in support activities that generally cut across service lines. The defense agencies have consolidated functions that were previously fractionalized among the military services. Among these agencies were the National Security Agency (NSA), which held responsibility for signals intelligence and cryptography; the Defense Advanced Research Projects Agency (DARPA), responsible for military research and development; the Defense Intelligence Agency (DIA), responsible for military intelligence; and the National Reconnaissance Office, which designs and maintains reconnaissance satellites for use by the Department of Defense and the intelligence community.

The need for the military to consider implications of political, economic, and scientific factors in the development of military plans and military advice requires that senior military officers have a broad education in these disciplines. To this end, the military departments have established an extensive continuing education system for their officers. Included in this educational system are joint-service schools such as the Joint Forces Staff College and National Defense University, as well as individual service schools such as the Naval War College, Air University, and Army War College. These schools offer graduate school-level programs to train future military leaders as broadly educated officers who understand the importance of political, economic, and scientific factors on military planning.

The Department of the Army, through its Corps of Engineers, also performs important civil functions in improving rivers, harbours, and waterways for navigation, in constructing flood-control and similar projects in various parts of the country, and in administering the laws governing navigable waters.

Proposals to coordinate the activities of the military services were initially considered by U.S. Congress in 1944. Specific plans were put forth in 1945 by the Army, the Navy, and the Joint Chiefs of Staff . In a special message to U.S. Congress on December 19, 1945, President Harry Truman proposed creation of a unified Department of National Defense. A proposal reached Congress in April 1946, but was held up by the Naval Affairs Committee held hearings in July 1946 due to objections to the concentration of power in a single department. Truman eventually sent new legislation to Congress in February 1947, where it was debated and amended for several months.

On July 26, 1947, Truman signed the National Security Act of 1947, which set up the National Military Establishment to begin operations on September 18, 1947, the day after the confirmation of James V. Forrestal as the first Secretary of Defense. The Establishment had the unfortunate abbreviation 'NME' (the obvious pronunciation being "enemy"), and was renamed the "Department of Defense" on August 10, 1949; in addition, the secretary was given greater authority over the military departments of the Army, Navy, and Air Force.

The Department was created by combining the War Department (founded in 1789) with the Navy Department (founded in 1798; formerly the Board of Admiralty, founded in 1780), and the newly created Department of the Air Force. The Department was formed in order to reduce interservice rivalry which was believed to have reduced military effectiveness during World War.

The command structure of the Department of Defense underwent several revisions but most recently was defined by the Goldwater-Nichols Act of 1986. Under the act, the chain of command ran from the President of the United States , through the Secretary of Defense, to the unified combatant commanders. The Chairman of the Joint Chiefs of Staff and the several Chiefs of Staff were responsible for readiness of the U.S. military and served as the President's military advisers, but were not in the chain of command. The Chairman of the Joint Chiefs of Staff was by law the highest ranking military officer in the United States.