The guided missile cruiser USS Princeton (CG 59) pulls alongside USS Nimitz in preparation for a Replenishment At Sea (RAS). The ability to refuel at sea allows the U.S. Navy to be where needed, when needed, and for as long as needed. Nimitz is currently conducting Battle Group Sustainment Exercises off the coast of southern California. U.S. Navy photo by Photographer?s Mate Airman Kristi Earl.