A wet sub is a type of underwater vehicle (submarine) that does not provide a dry environment for its occupants. Usually, wetsuited scuba divers will ride upon the device (as one would ride a motorcycle or with an opening as in an Olympic bobsled), although it can be designed to fully enclose its occupant(s) to provide lower drag. An enclosed vehicle may provide a dry viewing chamber for the occupant(s). The motive force is an electric motor and usually the power source is an electric battery. The depth and duration at depth is typically limited by the requirements of a scuba diver.