Inside a small building surrounded by a gate on a military base in Anchorage, Alaska, sits one of North America's most important first lines of defense.
Maj. Christopher Perham unlocks the gate that leads in, followed by a series of doors.
"This is the base of our operations here," Perham says.
He's part of the Alaska Air National Guard in the 176th Air Defense Squadron. But he works for the North American Aerospace Defense Command, better known as NORAD, which is headquartered thousands of miles away in Colorado.