Senior Airman Michael Daniel, 28th Maintenance Squadron hydraulics journeyman, lubricates seals for an auxiliary power unit piston in the 28th MXS Hydraulics Shop at Ellsworth Air Force Base, S.D., Jan. 19, 2012. The APU is a used to start B-1B engines to ensure the readiness of the base’s fleet of bombers. (U.S. Air Force Photo by Airman 1st Class Kate Thornton/Released)