The exercise run by the Joint Chiefs of Staff was under consideration in April 2001. It was meant to help national military leaders respond in a crisis if the Pentagon's operations centers were somehow taken out of action, either in an accident or an attack, said Lt. Col. Barry Venable, a Defense Department spokesman.
Officers at the North American Aerospace Defense Command (NORAD) suggested the scenario, one of several proposals rejected by the exercise planners, military officials said. They did not know what final scenario was used.
Military officials acknowledged the proposed exercise after the Project On Government Oversight circulated an e-mail that it said was from a former NORAD officer to some of his colleagues. The writer said that the Joint Chiefs rejected the hijacking scenario as unrealistic.
The exercise planning is apparently one of a few places, including a Tom Clancy thriller, where people proposed the idea of airliners being used as weapons. Before the Sept. 11 attacks, the threat was never considered by U.S. security agencies as among the most likely scenarios for terrorists to strike the United States.