The Military Sealift Command (MSC) is a United States Navy organization that controls the replenishment and military transport ships of the Navy. The United States Military Sealift Command has the responsibility for providing sealift and ocean transportation for all US military services as well as for other government agencies. It first came into existence on 9 July 1949 when the Military Sea Transportation Service (MSTS) became solely responsible for the Department of Defense's ocean transport needs. The MSTS was renamed the Military Sealift Command in 1970.
Military Sealift Command ships are made up of a core fleet of ships owned by the United States Navy and others under long-term-charter augmented by short-term or voyage-chartered ships. The Navy-owned ships carry blue and gold stack colors, are in service with the prefix USNS (United States Naval Ship), rather than in commission (a USS prefix), have hull numbers as an equivalent commissioned ship would have with the prefix T- and are civilian manned by either civil service mariners or contract crews (see United States Merchant Marine) as is the case of the special mission ships. Ships on charter or equivalent, retain commercial colors and bear the normal merchant MV, SS, or GTS without hull numbers.