U-2501

The first project for submarines designed specifically to stay most of the time underwater was Project XXI. They were equipped with improved batteries and a snorkel—a device that enabled the use of diesel engines for underwater movement. These submarines were also equipped with low-noise electric motors, allowing them to stealthily approach their targets. The lead submarine of the series, U-2501, did not participate in combat patrols and was sunk in Hamburg on May 3, 1945.