For the first time, a woman has taken command of the Cheyenne Mountain Operations Center in Colorado Springs.
The center is the military's secretive complex that tracks airborne threats over North America.
Air Force Brigadier General Rosanne Bailey is a 28-year military veteran.
Bailey will lead U.S. and Canadian efforts to defend North America from air and missile attacks. Bailey is the former commander of an air base wing at Ramstein Air Force Base in Germany.
She says she will have to learn quickly about her new job. Most of her career has been spent helping the service develop and purchase weapons.
Bailey replaces Brigadier General Duane Deal, a former spy plane pilot who helped investigate the crash of the Columbia space shuttle. Deal is retiring.
Bailey officially takes over the job Monday.