A submarine is a watercraft capable of independent operation below the surface of the water. It differs from a submersible, which has more limited underwater capability...
under 150 tons, typically operated by a crew of one or two but sometimes up to 6 or 8, with little or no on-board living accommodation. Midget submarines normally work with mother ships, from which they are launched and recovered, and which provide living accommodation for the crew and other support staff.
Both military and civilian midget submarines have been built.