On August 10, 1941, construction began on the Pentagon in Arlington, Virginia, designed to consolidate the War Department's sprawling, scattered offices into a single building. The five-sided design was chosen partly because of the irregular pentagon-shaped plot of land originally selected, and the building was rushed to completion in just 16 months, becoming one of the largest office buildings in the world.
By 1941, the U.S. War Department was scattered across 17 buildings in Washington, an inefficiency that alarmed planners bracing for likely war. Brigadier General Brehon Somervell proposed a single massive headquarters and gave architects a single weekend to produce preliminary plans. The chosen site, Arlington Farms, was an oddly shaped five-sided plot bounded by roads, which is why the building took its distinctive pentagonal shape—even after the site was later shifted slightly, planners kept the five-sided design already underway.
Ground was broken on August 10, 1941, just four months before Pearl Harbor. Construction proceeded at a wartime pace: up to 15,000 workers labored in shifts around the clock, pouring concrete (chosen over steel, which was needed for ships and tanks) into what would become 6.6 million square feet of floor space, 17.5 miles of corridors, and five above-ground floors surrounding a central courtyard.
The building was completed in January 1943 at a cost of about $83 million, astonishingly fast by any era's standards. It became not just the headquarters of the U.S. military but a global shorthand for American defense power itself—so much so that on September 11, 2001, it would become a target, absorbing a hijacked airliner into its western face and losing part of one of its five iconic wedges before being rebuilt within a year.
Key people: Brehon Somervell, Franklin D. Roosevelt