In the two years before the Sept. 11 attacks, the North American Aerospace Defense Command conducted exercises simulating what the White House says was unimaginable at the time: hijacked airliners used as weapons to crash into targets and cause mass casualties. One of the imagined targets was the World Trade Center. In another exercise ... the target was the Pentagon - but that drill was not run after Defense officials said it was unrealistic, NORAD and Defense officials say. NORAD, in a written statement, confirmed that such hijacking exercises occurred. Numerous types of civilian and military aircraft were used as mock hijacked aircraft," the statement said. "These exercises tested track detection and identification; scramble and interception; hijack procedures; internal and external agency coordination and operational security and communications security procedures." On April 8, the commission investigating the Sept. 11 attacks heard testimony from national security adviser Condoleezza Rice that the White House didn't anticipate hijacked planes being used as weapons. President Bush said ... "Nobody in our government ... could envision flying airplanes into buildings on such a massive scale." One operation, planned in July 2001 ... involved planes from airports in Utah and Washington state that were "hijacked." NORAD officials have acknowledged that "scriptwriters" for the drills included the idea of hijacked aircraft being used as weapons. "Threats of killing hostages or crashing were left to the scriptwriters to invoke creativity and broaden the required response," Maj. Gen. Craig McKinley, a NORAD official, told the 9/11 commission.