Staff Sgt. John Skipper, 57th Aircraft Maintenance Squadron Viper Aircraft Maintanence Unit aerospace propulsion craftsman, works on an engine at Detachment 13, 372nd Training Squadron on Nellis Air Force Base, Nev., Sept. 10, 2015. Detachment 13 gives Airmen advanced specialized training skills needed to help further their units’ missions. (U.S. Air Force photo by Airman 1st Class Rachel Loftis)