The term "11 sep pentagon" functions as a compound proper noun, designating the terrorist attack that occurred on September 11, 2001, at the headquarters of the United States Department of Defense in Arlington, Virginia. This event was one of four coordinated attacks carried out by the Islamic terrorist group al-Qaeda against the United States on that day. The phrase specifically identifies the location and date of this act, distinguishing it from the concurrent attacks in New York City and Pennsylvania.
The attack was executed when American Airlines Flight 77, a Boeing 757, was hijacked by five al-Qaeda terrorists after its departure from Washington Dulles International Airport. The hijackers deliberately crashed the aircraft into the western facade of the Pentagon at 9:37 a.m. EDT. The impact and subsequent fire caused a partial collapse of the building's structure. The crash resulted in the deaths of all 64 people aboard the aircraft (including the five hijackers) and 125 personnel within the Pentagon, totaling 189 fatalities.
The attack on the Pentagon held profound symbolic and strategic significance, as it was a direct assault on the nerve center of the U.S. military. The section of the building that was struck had recently been renovated with blast-resistant windows and structural reinforcements, a factor credited with saving many lives. The subsequent response involved a massive rescue and recovery effort, followed by a reconstruction project known as the "Phoenix Project," which was completed in under a year. This event was a critical component of the casus belli that precipitated the U.S.-led War on Terror.
