pentagon 4

On July 28 Congress authorized funding for a new Department of War building in Arlington, which would house the entire department under one roof,^[15] and President Roosevelt officially approved of the Hoover Airport site on September 2.^[16] While the project went through the approval process in late July 1941, Somervell selected the contractors, including John McShain, Inc. of Philadelphia, which had built Washington National Airport in Arlington, the Jefferson Memorial in Washington, and the National Naval Medical Center in Bethesda, Maryland, along with Wise Contracting Company, Inc. and Doyle and Russell, both from Virginia.^[17] In addition to the Hoover Airport site and other government-owned land, construction of the Pentagon required an additional 287 acres (1.16 km²), which were acquired at a cost of $2.2 million.^[18] The Hell's Bottom neighborhood, a slum with numerous pawnshops, factories, approximately 150 homes, and other buildings around Columbia Pike, was also cleared to make way for the Pentagon.^[19] Later 300 acres (1.2 km²) of land were transferred to Arlington National Cemetery and to Fort Myer, leaving 280 acres (1.1 km²) for the Pentagon.^[18]
Contracts totaling $31,100,000 were finalized with McShain and the other contractors on September 11, and ground was broken for the Pentagon the same day.^[20] Among the design requirements, Somervell required the structural design to accommodate floor loads of up to 150 pounds per square inch, which was done in case the building became a records storage facility at some time after the end of the current war.^[16] A minimal amount of steel was used as it was in short supply during World War II. Instead, the Pentagon was built as a reinforced concrete structure, using 680,000 tons of sand dredged from the Potomac River, and a lagoon was created beneath the Pentagon's river entrance.^[21] To minimize steel, concrete ramps were built rather than installing elevators.^[22][23] Indiana limestone was used for the building's facade.^[24]

Northwest exposure of the Pentagon's construction underway, July 1, 1942

Architectural and structural design work for the Pentagon proceeded simultaneously with construction, with initial drawings provided in early October 1941, and most of the design work completed by June 1, 1942. At times the construction work got ahead of the design, with different materials used than specified in the plans. Pressure to speed up design and construction intensified after the attack on Pearl Harbor on December 7, 1941, with Somervell demanding that 1,000,000 sq ft (9.3 ha) of space at the Pentagon be available for occupation by April 1, 1942.^[25] David J. Witmer replaced Bergstrom as chief architect on April 11 after Bergstorm resigned due to charges, unrelated to the Pentagon project, of improper conduct while he was president of the American Institute of Architects.^[26]