The names of all in service ships and naval bases of the Indian Navy are prefixed with the letters INS, designating Indian Naval Ship or Indian Navy Station,[150] whereas the sail boats are prefixed with INSV (Indian Naval Sailing Vessel).[151] The fleet of the Indian Navy is a mixture of domestic built and foreign vessels, as of January 2018[update], the surface fleet comprises 1 aircraft carrier,[152][153] 1 amphibious transport dock,[154] 8 Landing ship tanks,[154][155] 11 destroyers,[152] 13 frigates,[156][157] 23 corvettes,[156][158][159][160] 10 large offshore patrol vessels,[161] 4 fleet tankers,[162] 7 Survey ships,[163] 1 research vessel,[151] 3 training vessels[151] and various auxiliary vessels, Landing Craft Utility vessels,[155] and small patrol boats.[162][164]