On 11 September 2001, coincidentally the 60th anniversary of the Pentagon's groundbreaking, a team of five al-Qaeda affiliated hijackers took control of American Airlines Flight 77, en route from Washington Dulles International Airport to Los Angeles International Airport, and deliberately crashed the Boeing 757 airliner into the western side of the Pentagon at 9:37 am EDT as part of the September 11, 2001 attacks.
The impact of the plane severely damaged the outer ring of one wing of the building and caused its partial collapse.
At the time of the attacks, the Pentagon was under renovation and many offices were unoccupied, resulting in fewer casualties.
Only 800 of 4,500 people who would have been in the area were there because of the work.
Furthermore, the area hit, on the side of the Heliport facade, was the section best prepared for such an attack.
The renovation there, improvements which resulted from the Oklahoma City bombing, had nearly been completed.

It was the only area of the Pentagon with a sprinkler system, and it had been reconstructed with a web of steel columns and bars to withstand bomb blasts.
The steel reinforcement, bolted together to form a continuous structure through all of the Pentagon's five floors, kept that section of the building from collapsing for 30 minutes—enough time for hundreds of people to crawl out to safety.
The area struck by the plane also had blast-resistant windows—2 inches thick and 2,500 pounds each—that stayed intact during the crash and fire.
It had fire doors that opened automatically and newly built exits that allowed people to get out.

Contractors already involved with the renovation were given the added task of rebuilding the sections damaged in the attacks.
This additional project was named the "Phoenix Project," and was charged with having the outermost offices of the damaged section occupied by 11 September 2002.

When the damaged section of the Pentagon was repaired, a small indoor memorial and chapel were added at the point of impact.
For the fifth anniversary of the 11 September 2001 attacks, a memorial of 184 beams of light shone up from the center courtyard of the Pentagon, one light for each victim of the attack.
In addition, an American flag is hung each year on the side of the Pentagon damaged in the attacks, and the side of the building is illuminated at night with blue lights.
After the attacks, plans were developed for an outdoor memorial, with construction underway in 2006.
This Pentagon Memorial consists of a park on 2 acres (8,100 m²) of land, containing 184 benches, one dedicated to each victim.
The benches are aligned along the line of Flight 77 according to the victims' ages, from 3 to 71.
The park opened to the public on 11 September 2008.
On 11 September 2001, coincidentally the 60th anniversary of the Pentagon's groundbreaking, a team of five al-Qaeda affiliated hijackers took control of American Airlines Flight 77, en route from Washington Dulles International Airport to Los Angeles International Airport, and deliberately crashed the Boeing 757 airliner into the western side of the Pentagon at 9:37 am EDT as part of the September 11, 2001 attacks. The impact of the plane severely damaged the outer ring of one wing of the building and caused its partial collapse. At the time of the attacks, the Pentagon was under renovation and many offices were unoccupied, resulting in fewer casualties. Only 800 of 4,500 people who would have been in the area were there because of the work. Furthermore, the area hit, on the side of the Heliport facade, was the section best prepared for such an attack. The renovation there, improvements which resulted from the Oklahoma City bombing, had nearly been completed.
It was the only area of the Pentagon with a sprinkler system, and it had been reconstructed with a web of steel columns and bars to withstand bomb blasts. The steel reinforcement, bolted together to form a continuous structure through all of the Pentagon's five floors, kept that section of the building from collapsing for 30 minutes—enough time for hundreds of people to crawl out to safety. The area struck by the plane also had blast-resistant windows—2 inches thick and 2,500 pounds each—that stayed intact during the crash and fire. It had fire doors that opened automatically and newly built exits that allowed people to get out.
Contractors already involved with the renovation were given the added task of rebuilding the sections damaged in the attacks. This additional project was named the "Phoenix Project," and was charged with having the outermost offices of the damaged section occupied by 11 September 2002.
When the damaged section of the Pentagon was repaired, a small indoor memorial and chapel were added at the point of impact. For the fifth anniversary of the 11 September 2001 attacks, a memorial of 184 beams of light shone up from the center courtyard of the Pentagon, one light for each victim of the attack. In addition, an American flag is hung each year on the side of the Pentagon damaged in the attacks, and the side of the building is illuminated at night with blue lights. After the attacks, plans were developed for an outdoor memorial, with construction underway in 2006. This Pentagon Memorial consists of a park on 2 acres (8,100 m²) of land, containing 184 benches, one dedicated to each victim. The benches are aligned along the line of Flight 77 according to the victims' ages, from 3 to 71. The park opened to the public on 11 September 2008.
The Pentagon