At the end of World War II, Allied Occupation forces found hundreds of midget submarines built and building in Japan, including large numbers of the “Koryu” type. Many of these boats were in massed groups at shipyards and naval bases.
Royal Navy WW2 X-craft midget submarine. It is a little known fact that the first vessels off the coast of Normandy on 6th June 1944 were two midget submarines who guided the British forces towards the beaches.
The Confederate submarine H.L. Hunley was the first submarine to successfully sink an enemy warship, sinking the USS Housatonic on February 17, 1864. The Hunley sank while returning to Charleston Harbor, after the attack. This submarine was one of as many as a dozen Confederate midget submarines that were completely or partially built during the war, but was the only one to be used in battle. Of interest is that the designer was from Ohio and only a third of the crew was Southern.
Tirpitz - Operation "Source" using midget submarines x-craft (x-5, x-6, x-7, x-8, x-9, x-10). Destroyed midget submarine x-7 is on display at the Imperial War Museum, which made me curious as to how it came to be destroyed. The mission is explained here.
Tirpitz, sister of Bismarck (pictured nearby), September 1943. Based in Norwegian waters for much of the war, she was attacked 34 times by the British in attempts to remove her as a threat to the Arctic convoys, both by midget submarine (a VC winning action) and by carrier borne and heavy bombers. Already badly damaged, RAF Lancasters finished her off at Tromso in November 1944.