Wikipedia
A midget submarine (also called a mini submarine) is any submarine under 150 tons. Typically operated by a crew of one or two but sometimes up to 6 or 9, with little or no on-board living accommodation, they 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. Military types work with surface ships and other submarines as mother ships. Civilian and non-combatant military types are generally called submersibles, and normally work with surface ships.
Most early submarines, such as the United States Navy's Holland and the British Royal Navy's Holland 1, would now be considered midget submarines.
Usage examples of "midget submarine".
The two chatted about possible departure plans, George deciding that he'd take the next flight he could get on, Peggy saying that she wasn't sure how or when she was going to leave Helsinki--- that all she wanted to do right now was to walk and feel the sun bake her face and avoid any closed space that reminded her of a midget submarine, the backseat of a car, or a cramped train.
Through some oversight, they had been left set at their shallow setting, those put on for the midget submarine in Scapa, and had gone off almost directly under the ship.
You walk along the top of the midget submarine - it's not much wider than a plank and getting narrower and narrower as you move forward.
Every so often a team from a local college or museum would scour at the base and find fossilized shark teeth that had once belonged to a creature as large as a midget submarine, along with the bones of even more unlikely creatures that had lived here a hundred million years earlier.
Though he got away in a midget submarine, the Navy later reported it had sunk-so he's now in Davy Jones's locker.