U.S. Navy Master Chief Engineman Billy Shelton replaces a head gasket on an engine aboard the amphibious transport dock ship USS Mesa Verde (LPD 19) in the Atlantic Ocean Dec. 12, 2013. The Mesa Verde, with the embarked 22nd Marine Expeditionary Unit, was participating in a composite training unit exercise in preparation for deployment. (U.S. Navy photo by Mass Communication Specialist 3rd Class Shannon M. Smith/Released)