U.S. Air Force Gen. Lori Robinson became the military’s first female combatant commander as she assumed responsibility for U.S. Northern Command and North American Aerospace Defense in a ceremony Friday in Colorado. Robinson replaced outgoing Adm. William Gortney to lead the two commands. North American Aerospace Defense, or NORAD, is a joint U.S.-Canada operation tasked with detecting and tracking potential missile threats. U.S. Northern Command is responsible for the defense of the continental United States, but its area of operation also includes Mexico, Canada, the Gulf of Mexico and parts of the Caribbean.