The Pentagon’s basic design was drafted in four days. A day later, the plans were submitted to Congress for funding. Built September 1941–January 1943, it was the largest office building in the nation at the time. During World War II, the Pentagon (officially the U.S. Department of Defense headquarters) housed 33,000 employees. The building quickly became the premiere symbol of American military might. On 9/11, 2001, terrorists crashed American Airlines Flight 77 into the western side and more than 100 employees perished with the passengers and crew. A memorial has been completed and opened to the public. Tours of the Pentagon are also available.