An independent commission said Thursday that the United States air defense system was completely overwhelmed by the 2001 terrorist attacks on New York and Washington. U.S. military officials insisted that they would be able to handle such an attack today.

A staff report issued by the independent, bipartisan commission probing the nine-11 attacks said poor communications and confusion led to a breakdown in the air defense system after terrorists hijacked four airliners on September 11th.

One of the first indications of trouble came in a voice transmission from American Airlines Flight 11 bound from Boston to Los Angeles. The commission played a tape excerpt that is believed to be the voice of terrorist ringleader Mohammed Atta telling passengers to remain calm.

TAPE: "Nobody move. Everything is OK. If you try to make any move, if you try to make any move, you will endanger yourself and the airplane. Just stay quiet."

The 9/11 commission says controllers on the ground were slow to grasp what was happening in the air, especially after indications that three more planes had been hijacked.

The commission played other tape excerpts in which several air traffic controllers can be heard agonizing over whether to get the military involved.

TAPE Voice1: "We have a problem here. We have a hijacked aircraft headed towards New York and we need you guys to, we need someone to scramble some F-16's or something up there to help us out."

TAPE Voice2: "Is this real world or exercise?"

TAPE Voice1: "No, this is not an exercise, not a test."

TAPE Voice2: "Ah, do we want to think about scrambling [military] aircraft?"

TAPE Voice1: "Ah, God, I don't know."

TAPE Voice2: "That is a decision somebody is going to have to make sometime in the next ten minutes."

TAPE Voice1: "You know, everybody just left the room."

The commission says Vice President Dick Cheney had given the order for military jets to shoot down the hijacked aircraft, but the panel says the order did not reach the military pilots until after all four passenger jets had crashed.

Nearly 3000 people died on September 11 after planes crashed into the World Trade Center in New York, the Pentagon near Washington and a field in Pennsylvania.

Commission staff director Philip Zelikow says both the military and civilian components of the national air defense system were simply overwhelmed by the events of September 11.

"NORAD [North American Air Defense Command] and the FAA [Federal Aviation Administration] were unprepared for the type of attacks launched against the United States on September 11, 2001," he said. "They struggled, under difficult circumstances, to improvise a homeland defense against an unprecedented challenge they had never encountered and had never trained to meet."

U.S. military officials sought to assure the 9/11 panel that they have made significant improvements since the attacks.

Air Force General Richard Myers is chairman of the military Joint Chiefs of Staff and had this to say.

"And as you know, our posture today is quite a bit different as we look at this threat and other potential threats," he noted. "So we have improved our communications and we have refined our procedures, both with the White House and with the FAA and those procedures are in effect and are exercised."

And the commander of the North American Aerospace Defense Command, General Ralph Eberhart, said the changes made in communications, preparation and training would mean a different outcome if the same attacks were attempted again. "Because of the fixes, the remedies put in place, we would be able to shoot down all three aircraft, all four aircraft," he said.

Thursday's hearing was the final public session for the 9/11 commission. The panel will issue a final report late next month.