WASHINGTON (AP) -- Memories of horror and heroism echoed Sunday across the west side of the Pentagon where,a decade ago, a hijacked airplane carrying 59 doomed passengers and crew and 36,200 pounds of jet fuel smashed into the fortress-like military headquarters, killing all aboard and 125 inside.
At a ceremony attended by an estimated 1,600 people, including 1,200 relatives of the victims, Vice President Joe Biden joined Defense Secretary Leon Panetta and Navy Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, in paying solemn tribute to the families of the fallen.
They also highlighted the contributions of the U.S. military since Sept. 11, 2001.
"A generation of Americans stepped forward to serve in uniform, determined to confront our enemies and respond to them swiftly and justly," Panetta said.
After a moment of silence at 9:37 am EDT -- the exact time the Pentagon was hit by the jetliner -- the Navy Sea Chanters Chorus sang "Amazing Grace."
Mullen offered his condolences to the families, who sat in rows of metal chairs facing the outdoor Pentagon 9/11 Memorial near where the plane struck.
"No music can assuage, no tongue can express, no prayer alone may dampen the yearning that must fire yet inside you," he said. "Lives ended in this place. Dreams were shattered. Futures were instantly altered. Hopes were tragically dashed."
Biden offered an uplifting message of resilience.
"It's a basic American instinct to respond to crises when help is needed to confront the afflicted," Biden said. "An American instinct summoned by the collective strength of the American people that we come to the fore in our darkest hours; an instinct that echoes through the ages from Pearl Harbor to Beirut; from Mogadishu to Ground Zero; from Flight 93 to right here in the Pentagon."
President Barack Obama planned to lay a wreath at the Pentagon memorial later Sunday.
Many details of what transpired that bright, sunny morning in 2001 have been forgotten, or set aside, in the whirl of events in the intervening years.
The Boeing 757, with a wingspan of 124 1/2 feet, slammed into the west face of the Pentagon at ground level, traveling at 530 mph. The instant the nose of the plane made contact a fireball burst upward and rose 200 feet above the roof, according to the Pentagon's official history of the attack. The front of the fuselage disintegrated, but the midsection and rear-end continued inward, cutting a 270-foot path of destruction.
Robert Burns can be reached on Twitter (at)robertburnsAP