Schwertwal

"Sword Whale") was a German miniature submarine design that reached the trial stage in late April 1945.

It had a crew of two and was designed to have a high subsurface speed of around 20 knots.

The submarine lacked a periscope and the pilot viewed the outside world through an acrylic glass dome.

[1] The prototype was scuttled at the end of World War II but was raised by the British Navy and examined before being scrapped.

[1] Design work for an even faster version began but the plans never left the drawing board.