U.S. Air Force Maj. David McGraw, a combat rescue officer assigned to Air Combat Command, prepares for oxygen deprivation training at Langley Air Force Base, Va., April 19, 2016. After their initial training with the Reduced Oxygen Breathing Device, aircrew members must re-qualify with aerospace physiology every five years. (U.S. Air Force photo by Airman 1st Class Kaylee Dubois)