At sea aboard naval vessels, messing is still separate, with E-6 and below utilizing the ship's mess decks, E-7 through E-9 utilizing the ship's CPO Mess, and commissioned officers being part of the wardroom. Certain large vessels (e.g., aircraft carriers, amphibious assault ships) may also include a First Class Mess for E-6, typically a separate dining area adjacent to the mess decks. This is considered a chance for future CPOs to learn how to be a part of a mess before they enter the CPO Mess, often called by the sobriquet of "goat locker." Enlisted personnel normally receive all meals at what appears to be no cost, but in fact subsidize their meals through forfeiture of their Basic Allowance for Subsistence (BAS), also called "commuted rations," although Chief Petty Officers may also have a mess "buy in" or monthly mess bill equivalent to the BAS. For those ships with embarked Marine Corps personnel, staff noncommissioned officers in the grades of E-7, E-8 and E-9 will also be part of the CPO Mess. Commissioned Officers retain their BAS, a flat-rate allowance much smaller than the graduated by rank amount paid out to enlisted personnel; however, they must pay for all of their meals while afloat out of pocket. This usually entails a mess "buy in" as a member of the officers' mess and will typically have either a monthly mess bill or will purchase meals via some sort of debit card.