Before sunrise on September 11, 1941, the patch of Virginia ground across the Potomac from Washington was still more landscape than landmark. By the end of that day, the United States had formally begun building a headquarters on a scale no government had attempted before. The country was not yet a combatant in the Second World War, but the emergency that produced the Pentagon had already arrived.
This is the story of how wartime expansion, bureaucratic congestion and an almost impossible construction schedule produced the five-sided building that became the nerve center of American military power.
A capital running out of room
By the summer of 1941, the U.S. War Department had become a physical expression of the national emergency. Germany controlled much of continental Europe. Britain and the Soviet Union were fighting for survival. The United States remained formally neutral, yet rearmament, conscription and aid to the Allies were rapidly enlarging the military establishment.
War Department employees were dispersed through Washington in the Munitions Building, temporary offices and leased spaces. Coordination suffered because people, files and decisions had to move between dozens of locations. Brigadier General Brehon B. Somervell, head of the Construction Division of the Quartermaster Corps, argued that a single enormous headquarters could bring much of this machinery together.
The proposal moved with extraordinary speed. Somervell’s team presented the basic concept in July 1941. Congress authorized funding in August. The chosen area shifted away from the original Arlington Farms tract so that the view from Arlington National Cemetery toward Washington would be less obstructed. The irregular geometry associated with the first site nevertheless survived in the building’s famous five-sided plan.
Ground broken on September 11
Construction officially began on September 11, 1941. Colonel Leslie R. Groves, who later directed the Manhattan Project, supervised the work for the Army Corps of Engineers. Architect George Edwin Bergstrom led the design, with David J. Witmer later taking over as chief architect. The task was not simply to erect a large office block. It was to design while building, accommodate a workforce that was still growing and do so while strategic materials were being reserved for defense production.
The site itself created problems. Much of the ground was low and marshy. Engineers drove thousands of concrete piles and moved vast quantities of earth. Steel was scarce, so the project relied heavily on reinforced concrete. Sand and gravel could be dredged from the nearby Potomac, turning geography into part of the supply chain.
The schedule was relentless. Work continued around the clock in shifts. Plans were revised while foundations, roads and utilities were already taking shape. The Japanese attack on Pearl Harbor on December 7, less than three months after the groundbreaking, transformed urgency into wartime necessity. What had begun as preparation for a possible conflict became infrastructure for a nation at war.
Why five rings worked
The Pentagon’s shape is memorable, but its real achievement was circulation. Five concentric rings, linked by radial corridors, allowed tens of thousands of employees to move through a building containing millions of square feet without the journeys one might expect in a conventional block. The design placed offices around courtyards and exterior walls, bringing daylight and ventilation into a vast structure.
The building rose only five stories above ground, in part because wartime planners wanted to avoid elevators and the steel they required. Ramps connected floors. The low profile spread the offices horizontally, while the rings and spokes shortened routes between them. The central courtyard created an open core within the dense plan.
These decisions were products of scarcity as much as design philosophy. The Pentagon was not conceived as a timeless monument. Officials initially imagined that parts of it might serve other purposes after the emergency. Its endurance was an unintended consequence of a project built for speed.
Occupied before it was finished
Employees began moving into completed sections while construction continued elsewhere. The building was completed in January 1943, roughly sixteen months after work began. By then it was already functioning as the center of a global war effort, housing senior military leaders and the administrative systems behind operations in Europe, North Africa and the Pacific.
The speed of construction did not mean the project was simple or uncontroversial. Its cost, scale and location attracted criticism. Yet the administrative problem it addressed was real: the United States was building armed forces capable of operating across oceans, and command structures needed to expand with them.
From 1942 until the creation of the Department of Defense, the building housed the War Department. After the National Security Act reorganized the armed services, the Pentagon became the headquarters associated with the new defense establishment. A temporary answer to wartime congestion became a permanent institution.
The date’s later echo
Sixty years to the day after construction began, American Airlines Flight 77 struck the Pentagon during the September 11 attacks of 2001. The coincidence gave the date an extraordinary double meaning in the building’s history: September 11 marked both its physical beginning and the deadliest attack it had endured.
Renovation work under way before the attack had strengthened part of the affected wedge. The building was repaired and reoccupied, while a memorial outside now names the 184 people killed aboard Flight 77 and at the Pentagon.
Why the Pentagon groundbreaking matters
The groundbreaking reveals how institutions are shaped by emergencies. The Pentagon’s form grew from hurried decisions about land, materials, circulation and administrative need. Its completion demonstrated the mobilizing capacity that the United States would bring to the Second World War. Its later history made it a symbol far beyond architecture.
For more wartime turning points, explore the World War II archive, including the U.S. declaration of war on Japan, the opening of the Guadalcanal campaign, and the liberation of Antwerp. Return to the complete Today in History edition for September 11.
Sources and method. This article was checked against the U.S. Department of Defense Historical Office’s Pentagon history and institutional histories of the building and its wartime construction. Scene-setting is limited to documented conditions; no dialogue or individual thoughts have been invented. Images labeled as reconstructions are editorial illustrations, not archival photographs.
Written and fact-checked by the Discover Today in History editorial team. Last reviewed September 10, 2026.
From my childhood as a boomer, I no longer have my mother to confirm that she worked at the Pentagon in the last years of WWII into about 1947. Is there a way to check that out? Dad was in DC on Army assignment to process troops out as they returned from the European theater !