Government officials agreed that the War Department building, officially designated Federal Office Building No 1, should be constructed across the Potomac River, in Arlington County, Virginia. Requirements for the new building were that it be no more than four stories tall, and that it use a minimal amount of steel to reserve that resource for war needs. The requirements meant that, instead of rising vertically, the building would be sprawling over a large area. Possible sites for the building included the Department of Agriculture's Arlington Experimental Farm, adjacent to Arlington National Cemetery, and the obsolete Hoover Field site.
The site originally chosen was Arlington Farms, which had an asymmetric, roughly pentagonal shape, so the building was planned accordingly as an irregular pentagon.[23] Concerned that the new building could obstruct the view of Washington, D.C., from Arlington Cemetery, President Roosevelt ended up selecting the Hoover Airport site instead.[24] The building retained the pentagonal layout because Roosevelt liked it and a major redesign at that stage would have been costly. Freed of the constraints of the Arlington Farms site, the building was modified as a regular pentagon. It resembled star forts constructed during the gunpowder age.[25]
On 28 July, Congress authorized funding for a new Department of War building in Arlington, which would house the entire department under one roof. President Roosevelt officially approved of the Hoover Airport site on 2 September. 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. 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 (equivalent to $30.3 million in 2020[1]). The Hell's Bottom neighborhood, consisting of numerous pawnshops, factories, approximately 150 homes, and other buildings around Columbia Pike, was cleared to make way for the Pentagon. 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.