Hai (Polish shark) is a prototype of a German miniature submarine of the Second World War. The ship was 11 meters long with a hull diameter of only 533 millimeters. The ship was armed with one torpedo. Probably only one copy of this ship was made. The Hai was designed as a modernized and improved version of the Marder miniature submarine, which was first used in combat in August 1944. Compared to its predecessor, the Hai was about 3 meters longer, allowing it to be equipped with more powerful batteries, which allowed it to reach an underwater speed of 20 knots, thus much faster than the Marder. The device could also stay under water for about 2 hours. However, in the course of the tests, the Hai turned out to be an extremely unsuccessful design and never went into production. The approaching end of the war also halted the possible development of these weapons.
