BARKSDALE AIR FORCE BASE, La. – Airman 1st Class Lucas Guthrie, 2nd Aircraft Maintenance Squadron crew chief, pumps liquid oxygen into a B-52 Stratofortress during a nuclear operational readiness exercise June 3. The liquid oxygen is converted to gas and provides breathable air to the aircrew at high altitudes. The exercise is preparing Barksdale AFB Airmen for the upcoming nuclear operational readiness inspection in mid-June. (U.S. Air Force photo/Senior Airman Chad Warren)