For a moment on 9/11, Colorado Springs military leaders thought the city was a target. For a moment, they had to assume the worst about reports of a California jetliner bound for Denver.
Emotions, already raw, rose even more inside Cheyenne Mountain Air Force Station when crews closed the mountain's blast doors.
Behind doors built to withstand a nuclear blast, the crew inside the mountain was safe. Outside the mountain, on the other side of the doors, laid bare to the sky, were their families and neighbors.
"It was that pucker factor," said Rusty Mullins, a career civilian worker with the 721st Mission Support Squadron at the mountain.
The mountain base was built during the Cold War as command post to coordinate defense of America and Canada in a nuclear war. On 9/11 a Cold War-style training exercise was under way inside the manmade cave. The attacks in New York and Washington seemed like a surreal addition to the training scenario.
"We didn't know what was going on, but really fast we knew," Mullins said. "It became very solemn and very organized at the same time."
Then came the report about a jetliner headed to Denver from California.
"We had intelligence that this aircraft was going to be hijacked and was heading for Cheyenne Mountain," Mullins said.
The plane never came. It was tracked down and landed safely as the North American Aerospace Defense Command worker inside the mountain grounded all nonmilitary flights nationwide.
That day changed everything about air defense at the mountain. Airmen still watch for incoming enemy missiles, but they also think about terror attacks, from inside U.S. airspace as well as far-away enemies.