PETERSON AIR FORCE BASE, Colo. — Air Force Gen. Lori J. Robinson on Friday became the first woman to lead a top-tier U.S. warfighting command when she took charge of the North American Aerospace Defense Command and U.S. Northern Command in Colorado. Robinson — one of just two female four-star generals in the Air Force — was "the clear and obvious choice," said Defense Secretary Ash Carter, who attended the change of command ceremony in a vast hangar at Peterson Air Force Base. Outside, a row of cannons fired a 19-gun salute.