ELLSWORTH AIR FORCE BASE, S.D. - Airman 1st Class Kymric Walker, 28th Maintenance Squadron aerospace propulsion apprentice, performs routine maintenance to a B-1B Lancer engine trailer by lubricating its wheel bearings, April 9. The engine trailers require routine maintenance to properly transport B-1 engines. (U.S. Air Force photo/Senior Airman Marc I. Lane)