Staff Sgt. Melvin D. Branch, 2nd Logistics Readiness Squadron cryogenics NCO in charge, refills a cart of liquid oxygen at Barksdale Air Force Base, La., April 28, 2020. Liquid oxygen is used in the B-52H Stratofortress during flight to combat hypoxia in aircrew at high altitudes. (U.S. Air Force photo by Airman 1st Class Jacob B. Wrightsman)