Diving bells are used as underwater search vessels and by working divers doing underwater work and salvage. The bell is lowered into the water by cables from a crane attached to a ship or dock. The bell is ballasted so as to remain upright in the water and to be negatively buoyant so that it sinks even when full of air.
Hoses, fed by pumps on the surface, provide compressed breathing gas to the bell, serving two functions: