Today it’s difficult to grasp how quickly all of this happened. Somervell’s crews worked while legislators, accustomed to a more deliberate pace, continued to debate the idea and offer suggestions and revisions. In his book The Pentagon: A History, author Steve Vogel describes the wrecking of the Hell’s Bottom slums as happening so quickly, few people were aware of it; as the buildings fell, dumbfounded patrons arrived on buses from the capital, clutching pawn tickets they hoped to redeem at shops that no longer existed.

The Pentagon was literally built faster than it could be designed. As Vogel’s books relates, the drafting team assembled by lead designer Ides van der Gracht was put to work in the basement of a Fort Myer warehouse, a former horse stable, so stuffy and hot that draftsmen sat shirtless at their work tables, covering their drawings with blotting paper to avoid ruining them with their sweat. Eventually a design force numbering about 350 was moved to a former airplane hangar on the old airport grounds.

Though the blueprint machines in the hangar produced an average of 15,000 yards of print paper a day, it wasn’t fast enough to keep up with the demands of site supervisors. Some simply based their work on what had already been built and hoped for the best. Decades later, when designers for the massive Pentagon Renovation Project looked for original drawings and materials specifications to use as references, they discovered that for many parts of the building, there weren’t any.

Somervell, to minimize his interactions with Congress and the public, remained cagey about what was actually going on in Hell’s Bottom, but in October 1941, after crews had made substantial progress, he released some details to the press. Projections of the War Department’s size had already increased, but Somervell had promised a three-story building, so the plan he revealed in October was described as a three-story building with a “basement” that observers couldn’t help noticing was above ground.

By July 1942, months after the Pearl Harbor attack and America’s entry into the war, the Pentagon was about two-thirds complete – but every square inch of it had already been assigned, and more room was needed to accommodate War Department employees. Somervell’s team, without consulting Congress, added a fifth floor to squeeze in another 300,000 square feet of office space. By now the project was already $14 million over its estimated cost, and budget hawks were outraged when the War Department released a new plan including a “fourth floor intermediate.” Today’s Pentagon is a five-story building with a mezzanine and basement.