U.S. Air Force Tech. Sgt. Dominic Valle from the 2nd Air Refueling Wing conducts a pressure test on a quick-don oxygen mask during exercise Vigilant Shield on 5 Wing Goose Bay, Canada, Oct. 25, 2014. The Vigilant Shield field training exercise is a bi-national NORAD Command exercise which provides realistic training and practice for American and Canadian forces in support of respective national strategy for North America???s defense. NORAD ensures U.S. and Canadian air sovereignty through a network of alert fighters, tankers, airborne early warning aircraft, and ground-based air defense assets cued by interagency and defense surveillance radars. (U.S. Air Force photo by Staff Sgt. Troy Anderson / RELEASED)