SOUTH CHINA SEA (Jan. 4, 2021) Sailors prepare to conduct tactical room-clearing during the Navy Security Force Sentry (NSFS) course on the flight deck aboard the Arleigh Burke-class guided-missile destroyer USS John S. McCain (DDG 56). McCain is assigned to Destroyer Squadron Fifteen (DESRON 15), the Navy�s largest forward-deployed DESRON and the U.S. 7th Fleet�s principal surface force. (U.S. Navy photo by Mass Communication Specialist 2nd Class Markus Castaneda)