Dec. 21, 2007 -- As travel time for the Christmas holiday begins to reach its peak, there is a secret army of people working behind the scenes to keep travelers safe.
ABC News got an exclusive look inside the Transportation Security Operations Center -- the nerve center of the government's efforts to protect people who are criss-crossing the country, especially those who fly.
The location of the facility is top secret, and it's so sensitive, cameras had never been allowed in before.
The Transportation Security Administration-run center is where the government attempts to achieve what's called situational awareness -- an effort to know what's happening in on the ground and in the sky -- all aimed at stopping a catastrophic terrorist attack.
"It's all about connecting the dots," TSA Deputy Assistant Director Don Zimmerman told ABC News.
A bank of huge monitors allows the government to track air traffic, everything in the sky from commercial to cargo to general aviation.
"I can discern within seconds which aircraft have federal air marshals onboard, which have the federal flight deck officers, the armed pilots on board," Zimmerman explained.
With 459 airports to monitor, there is always something going on. And the center's staff is always trying to keep track of the action.
"It ranges the full gamut," Zimmerman said. "Even today in a post 9/11 world, we still have people showing up with firearms."
Incident reports pour in from around the country, 24 hours a day, seven days a week -- each one tracked by computer. Bomb threats. Suspicious passengers. Airport evacuations.
During ABC News' visit to the center, security personnel at an airport in Colorado Springs, Colo., stopped an elderly woman with a cane. It might have seemed innocuous enough, but hidden inside the cane was a large knife.
"This is what we consider an artfully concealed weapon," Zimmerman said.
Often, the center deals with matters of life and death.
Airport personnel across the country communicate with the center using the Domestic Events Network, a secure audio bulletin that alerts the center to rapidly unfolding emergencies.
"Headquarters, Chicago," a radio squawked during one such situation Thursday.
"I've got a medical emergency for you," the Chicago caller said.
"The medical emergency is a possible heart attack. He is going into Milwaukee. It was originally off of Philadelphia."
Other critical information includes the possible targets of a plane that is in trouble, or worse, hijacked by terrorists. Those sites could include chemical or nuclear power plants.
"We want to know what else is out there, meaning if we are tracking an aircraft of interest, what critical infrastructure might be along the path of that aircraft," Zimmerman said.
The secret facility has several visible reminders to workers of why their mission is so critical: a twisted steel beam from the World Trade Center, a piece of United Flight 93's wreckage and fuel-stained granite from the Pentagon.