Pedestrian tunnel under Interstate 395 leading to the Pentagon in Arlington, Virginia (© Rozanne Hakala/Getty Images)

【January 15 2013】In 1941, the War Department employed 24,000 personnel, all focused on the increasing likelihood of the United States entering World War II. It was clear they'd need more space. On Thursday, July 17, Lt. Col. Hugh J. Casey and a civilian architect were ordered to develop plans – over the weekend – for an office building for 40,000. By Monday, the War Department had approved their innovative five-sided-building design, which would become known as the Pentagon.Explore breathtaking Gallery from the HuluTrip homepage over the past 5 years..