The Pentagon's Construction Timeline Construction of the Pentagon, the headquarters of the U.S. Department of Defense in Arlington, Virginia, began on September 11, 1941 , right as World War II ramped up American military needs. It was a feat of wartime urgency, designed by architect George Bergstrom under Brigadier General Brehon Somervell, and completed in just 16 months by January 15, 1943—making it the world's largest office building at over 6.5 million square feet.

Why So Fast?

  • Wartime Pressure : The War Department had outgrown scattered Washington, D.C., offices, needing one massive hub for 26,000 workers amid global conflict.
  • Innovative Design : Its iconic five-sided shape with five concentric rings (A-E) and 17 miles of corridors allowed rapid, modular building; workers poured concrete non-stop in three shifts.
  • Resource Smarts : To save steel, builders used concrete ramps instead of elevators and skipped fancy metals, finishing under budget at $83 million (about $1.5 billion today).

Fun Historical Tidbit

Imagine 4,000 laborers racing winter 1941-42 deadlines—one section was ready by April 1942 for early move-ins. The pentagonal layout stemmed from the site's odd shape, turning a constraint into a symbol of military might.

Key Milestones

  1. Groundbreaking : Sept. 11, 1941—eerily 60 years before 9/11 attacks that later struck it.
  1. First Occupancy : Spring 1942, as outer rings wrapped up.
  1. Dedication : Jan. 15, 1943, fully operational.

TL;DR : Built from Sept. 11, 1941, to Jan. 15, 1943, in a WWII building blitz.

Information gathered from public forums or data available on the internet and portrayed here.