The term refers to the terrorist attack on September 11, 2001, in which American Airlines Flight 77 was hijacked and deliberately crashed into the Pentagon in Arlington, Virginia. This event was one of four coordinated attacks carried out by the extremist group al-Qaeda against the United States on that day. The impact occurred at 9:37 AM EDT, striking the western side of the building, which serves as the headquarters of the U.S. Department of Defense.
The crash and subsequent fire caused a partial collapse of the building's structure. The attack resulted in 184 fatalities: all 64 people aboard the aircraft (including 59 passengers and crew, and 5 hijackers) and 125 military and civilian personnel inside the Pentagon. The section of the building that was hit had recently been renovated with reinforced steel columns, windows, and blast walls, a factor credited by structural engineers with preventing a more catastrophic collapse and saving numerous lives. The emergency response involved firefighters, law enforcement, and medical personnel from numerous local, state, and federal agencies.
As a direct assault on the nerve center of the United States military, the event was a profound symbolic and strategic blow. The physical damage prompted a major reconstruction effort known as the "Phoenix Project," which was completed in under a year. In remembrance of the victims, the Pentagon Memorial was constructed on the site and dedicated in 2008. The incident was a critical component of the broader 9/11 attacks that directly precipitated the U.S.-led "War on Terror," including military operations in Afghanistan and significant changes to national security and aviation protocols.
