170812-N-YG104-006 CORAL SEA (Aug. 12, 2017) A Marine assigned to the 31st Marine Expeditionary Unit (31st MEU) holds a security perimeter during a visit, board, search and seizure drill aboard the fleet replenishment oiler USNS Rappahannock (T-AO 204) as part of a certification exercise (CERTEX). During the CERTEX, the 31st Marine Expeditionary Unit (31st MEU) will be evaluated on crisis response operations for a number of potential contingencies. CERTEX is taking place off the coast and within the Shoalwater Bay Training Area, Australia, and will test the MEU’s ability to conduct all of its core missions such as stability operations, non-combatant evacuation and disaster relief. (U.S. Navy photo by Mass Communication Specialist 2nd Class Sarah Villegas/Released)