THE PENTAGON: Under the pressure of war, the Corps built the Pentagon in 16 months
Construction commenced on Sept. 1, 1941, and continued rapidly during the winter of 1941-42. Architects for the project had little or no lead time; sometimes construction actually outpaced planning. On Dec. 1, 1941, when the president signed legislation transferring the military construction mission from the Quartermaster Corps to the Army Corps of Engineers, 4,000 men were laboring on the building in three shifts. The basic shell and roof were finished in one year, and the building was completed by Jan. 15, 1943. More on the Corps' history.