On the U.S. President's desk in the Oval Office, a phone's red light urgentlyflashes. It's the signal for an incoming call. Only calls from deep inside thevast command-center redoubt known as Cheyenne Mountain come in on this line.Constructed during the Cold War, this hollowed-out mountain contains a virtualPentagon satellite-city built to survive a hundred years behind million-tonblast-proof doors.