The commission investigating the 2001 terrorist attacks in the United States says the nation's air-defense system was completely unprepared for the type of attack launched by al-Qaida.
The information was contained in a commission staff report released (Thursday), before the commission completed its 12th and final public hearing.
The report says aviation and military officials were forced to improvise to meet a challenge they had never trained for -- the use of aircraft as guided missiles.
It also says Vice President Dick Cheney authorized military jets to shoot down any planes headed for Washington, but the order did not reach pilots until the last of the four hijacked planes had crashed.
White House spokesman Scott McClellan says officials have made "significant improvements" to the nation's air defense procedures since that day.