apparatus, setup - equipment designed to serve a specific function

bathyscape, bathyscaph, bathyscaphe - navigable deep diving vessel for underwater exploration

bathysphere - spherical deep diving apparatus (lowered by a cable) for underwater exploration

diving bell - diving apparatus for underwater work; has an open bottom and is supplied with compressed air

minisub, minisubmarine - submersible vessel for one or two persons; for naval operations or underwater exploration

pigboat, submarine, U-boat, sub - a submersible warship usually armed with torpedoes

combat ship, war vessel, warship - a government ship that is available for waging war