U.S. Air Force Staff Sgt. Donovan Walters, 18th Component Maintenance Squadron aerospace propulsion craftsman, performs an engine test March 10, 2017, at Kadena Air Base, Japan. Units are tested for a variety of reasons, particularly when major components have been replaced. This testing helps to run new parts through the old system for functionality. (U.S. Air Force photo by Airman 1st Class Quay Drawdy)