1) Midget submarine 
The Schwertwal was a German miniature submarine design that reached the trial stage in late April 1945. It had a crew of 2 and was designed to have a high subsurface speed of around 20 knots. The high speed was archived by the use of a Walther turbine. The submarine carried an armament of two torpedoes. The submarine lacked a periscope and the pil...