The Pentagon

The Pentagon is the headquarters building of the United States Department of Defense, in Arlington County, Virginia, across the Potomac River from Washington, D.C. The building was constructed on an accelerated schedule during World War II. As a symbol of the U.S. military, the phrase The Pentagon is often used as a metonym for the Department of Defense and its leadership.

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 impetus to gain Congressional approval for the project. Colonel Leslie Groves was responsible for overseeing the project for the U.S. Army Corps of Engineers, which supervised it.

The Pentagon is the world's second-largest office building, with about 6.5 million square feet (600,000 m²) of floor space, 3.7 million square feet (340,000 m²) of which are used as offices. 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) of corridors, with a central five-acre (2.0 ha) pentagonal plaza. About 23,000 military and civilian employees work in the Pentagon, as well as about 3,000 non-defense support personnel.

In 2001, the Pentagon was damaged during the September 11 attacks. Five Al-Qaeda hijackers flew American Airlines Flight 77 into the western side of the building, killing themselves and 184 other people, including 59 on the airplane and 125 in the Pentagon. It was the first significant foreign attack on federal facilities in the capital area since the Burning of Washington during the War of 1812. Following the attacks, the western side of the building was repaired, with a small indoor memorial and chapel added at the point of impact. In 2009, an outdoor memorial dedicated to the Pentagon victims of the September 11 attacks was opened directly southwest of the building.

The Pentagon building spans 28.7 acres (116,000 m²; 11.6 ha), and includes an additional 5.1 acres (21,000 m²; 2.1 ha) as a central courtyard.

Starting with the north side and moving clockwise, its five façade entrances are the Mall Terrace, the River Terrace, the Concourse (or Metro Station), the South Parking, and the Pentagon Army Heliport. On the north side of the building, the Mall Entrance, which also features a portico, leads out to a 600-foot-long (180 m) terrace that is used for ceremonies. The River Entrance, which features a portico projecting out twenty feet (6 m), is on the northeast side, overlooking the lagoon and facing Washington. A stepped terrace on the River Entrance leads down to the lagoon; and a landing dock was used until the late 1960s to ferry personnel between Bolling Air Force Base and the Pentagon. The main entrance for visitors is on the southeast side, as are the Pentagon Metro station and the bus station.

There is also a concourse on the southeast side of the second floor of the building, which contains a mini-shopping mall. The south parking lot adjoins the southwest façade, and the west side of the Pentagon faces Washington Boulevard.

The concentric rings are designated from the center out as "A" through "E" with additional "F" and "G" rings in the basement. "E" Ring offices are the only ones with outside views and are generally occupied by senior officials. Office numbers go clockwise around each of the rings, and have two parts: a nearest-corridor number (1 to 10), followed by a bay number (00 to 99), so office numbers range from 100 to 1099. These corridors radiate out from the central courtyard, with corridor 1 beginning with the Concourse's south end. Each numbered radial corridor intersects with the corresponding numbered group of offices. Corridor 5, for instance, divides the 500 series office block. There are a number of historical displays in the building, particularly in the "A" and "E" rings.