Midget submarine

A midget submarine is any submarine under 150 tons, typically operated by a crew of one or two but sometimes up to six or nine, 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 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 would now be considered midget submarines, such as the United States Navy's USS Holland (SS-1) and the British Royal Navy's HMS Holland 1 (both named for the same designer).

Midget submarines are best known for harbor penetration, although only two World War II boats, the British X-craft and the unsuccessful Welman submarine, were specifically designed with this in mind. Japan's Ko-hyoteki-class submarines were originally designed to take part in decisive fleet actions. However, as circumstances changed, they were given the task of harbor penetration. Germany's various World War II designs were mostly designed to attack Allied shipping off landing beaches and harbors, although the Seehund had a great enough range to attack shipping off the Thames estuary.

Midget submarines have also seen some use in support roles. X-craft were used for reconnaissance, and the Seehund was used to carry supplies. A number of modern midget submarines have also been built for submarine rescue.

Midget submarines are commonly armed with torpedoes and mines in the form of, for example, detachable side loads and nose sections. Alternatively they may function as swimmer delivery vehicles to deliver frogmen to the vicinity of their targets, which are then attacked with limpet mines.

In civilian use, midget submarines are generally called submersibles; commercial submersibles are used in, for example, underwater maintenance, exploration, archaeology, and scientific research. Other commercially available submersibles are marketed as novelty tourist attractions and as specialised tenders for wealthy yacht owners. Also, a growing number of amateur submariners homebuilt submersibles as a hobby.

France also acquired a number of German midget submarines at the end of WW2.

Most German midget submarines were developed late in World War II in an attempt to stop the Allied liberation of Europe and used later to disrupt its supply lines. As a result, the submarines mostly engaged in open water attacks rather than harbour penetration.