Newly released recordings from civil and military aviation officials on 11 September 2001 conveys the confusion as the attacks of that day unfolded.
The audio includes a flight attendant's plea for help and discussions about an order from Vice-President Dick Cheney to shoot down rogue civilian planes.
Threats from one of the lead hijackers, Mohammed Atta, are also heard.
The audio was prepared for the 9/11 Commission, but was not completed before that inquiry reported in 2004.
Much of the material has been previously published in transcript form.
Among the recordings is a phone call from Betty Ong, a flight attendant on American Airlines Flight 11.
"Somebody's stabbed in business class, and, um I think there is Mace that we can't breathe," Ms Ong says. "I don't know, I think we're getting hijacked."
One of the hijackers, Mohammed Atta, is heard on the same plane saying: "Nobody move, everything will be OK.
"If you try to make any moves, you will injure yourself and the airplane. Just stay quiet."
Most of recordings come from the Federal Aviation Administration and are of controllers and the military officials working with them.
After Flight 11 hits the World Trade Center, controllers are heard as a second plane streaks past a radar control facility on its way to Manhattan.
"Another one just hit the World Trade," says a voice.
That is followed by: "The whole building just, ah, came apart."
When some fighter jets were scrambled eastward in the confusion, a military commander ordered them back to Washington as fast as possible.
"I don't care how many windows you break," Maj Kevin Nasypany says, several minutes before the last of the planes, United flight 93, crashes in Pennsylvania.
The order from the vice-president to shoot down unresponsive planes comes at about 10:30.