Airman Daniel Giulian, 437th Aircraft Maintenance Squadron crew chief, transfers liquid oxygen from a tank to a C-17 Globemaster III at dusk on Feb. 11, 2015, at Joint Base Charleston, S.C. When exposed to open air, the minus-297-degree LOX evaporates into a gas. Liquid oxygen is used as a means of distributing breathable air to aircrew members and passengers above 10,000 feet above sea level. The C-17 can hold approximately 155 gallons of LOX. (U.S. Air Force photo/Senior Airman Dennis Sloan)

Airmen from the 437th Aircraft Maintenance Squadron use a spotlight to illuminate the inside of a hangar at night, so they are able to perform maintenance on a C-17 Globemaster III Feb. 11, 2015, at Joint Base Charleston, S.C. AMXS Airmen work day and night maintaining the Charleston C-17 fleet and use various portable lighting systems to make nighttime maintenance possible. (U.S. Air Force photo/ Senior Airman Dennis Sloan

C-17 Globemaster IIIs line the ramp at dusk, Feb. 11, 2015, at Joint Base Charleston, S.C. Maintainers perform checks and maintenance on the aircraft day and night to ensure the aircraft are ready to fly. (U.S. Air Force photo/Senior Airman Dennis Sloan)