In a windowless, heavily fortified room packed with rows of computer screens and phones, there are many pairs of eyes keeping watch over U.S. airspace 24 hours a day.

Whether it's an American Airlines 767 flying from Seattle to Denver or a seaplane taking off from Lake Washington, if it's west of the Mississippi River, Washington Air National Guard airmen working at the Western Air Defense Sector at McChord Field know where it came from, where it's heading and how fast it's going.

Composed of about 330 guardsmen, civilian contractors and Canadian military personnel, WADS works with similar units in three other regions: Alaska, Canada and upstate New York. Together, the four sectors report to the North American Aerospace Defense Command, a bi-national command of the U.S. and Canada that provides aerospace surveillance, warning and assessment of aerospace attack, and maintains the sovereignty of U.S. and Canadian airspace.

Through a partnership with the Federal Aviation Administration and other federal entities that operate radar systems, WADS' mission includes detecting, identifying and defending against air threats.

"We watch everybody coming into the country," said Col. Paul Gruver, WADS commander. "Our challenge is identifying people who don't want to be seen or heard."

But the evolution of that mission has changed over the last 10 years. Prior to the Sept. 11 terrorist attacks, WADS' mission was more focused on Cold War posturing and defending against airborne threats invading the borders. The fact that the threat can now come from inside the borders puts a more narrow focus on WADS' mission.

While the $1 billon defense system WADS employs can gather the data, there has to be a staff of highly trained and experienced guardsmen interpreting everything.

"There has to be a translator - the only way it works is through our humans," said the 52-year-old Gruver, an F-16 pilot who also flies commercial aircraft for Delta.

When a threat is identified, the floor of the main control center is bustling with activity.

"That's when the team really comes together," said Master Sgt. Don Fillhart, a mission crew command technician who's worked at WADS since 1996.

The information gathering process picks up steam while guardsmen scramble to collect as much information about the threat as they can, using other agencies such as local law enforcement, U.S. Customs and Border Protection and the FAA.

"The thing we deliver is truth," Gruver said. "We partner with other agencies - those partnerships help fill the gaps of information."

With the goal being to get as much information as they can about the threat - in a short amount of time - sometimes that means getting a pair of eyes on the threat from a fighter jet scrambled from one of the many locations WADS can put on alert.

"It's essential we get eyes on the jet to access intent," Gruver said. "Looking into the cockpit is a key piece to seeing its capability."

With an open and frank dialogue with senior leaders, a decision is then made on the next course of action.

"We can decide to do something or decide to do nothing," Gruver said. "My job is to make sure the president or the secretary of defense has all the information he needs to make that decision."

While those situations that require a show of air defense can be few and far between, the WADS team is constantly preparing for the unknown.

"When we're not handling scrambles, we're training for other events," Fillhart said. "We've trained as part of so many different scenarios."

And there is long waiting list for those who want to be involved in the WADS mission, Gruver said.

"We're all very proud ... we're patriots," he said.