U.S. Marines assigned to Marine Medium Tiltrotor Squadron (VMM) 163 perform maintenance on an AH-1Z Viper helicopter aboard the amphibious transport dock ship USS San Diego (LPD 22) in the Pacific Ocean May 6, 2014. The San Diego was part of the Makin Island Amphibious Readiness Group and was underway in the U.S. 3rd Fleet area of responsibility participating in a composite training unit exercise in preparation for a scheduled deployment (U.S. Marine Corps photo by Gunnery Sgt. Rome M. Lazarus/Released)