Marder (Pine Marten) was a German midget submarine developed from the Neger. The craft was 8.3m (27.2feet) long and unlike the Neger included a flooding tank in the nose allowing it to dive. Another improvement was the dome through which the pilot viewed the outside world that also served as the craft's entrance and exit was made openable from the inside.[1] Maximum diving depth was about 25m (82feet).[2]
The submarine's first operations took place on the night of 2 August 1944, when Nazi Germany's Kriegsmarines Small Battle Units made their largest effort of the war. 58 human torpedoes[3] of the Neger-type and 22 Linse vessels were launched against Allied shipping off Normandy as part of a combined operation with Negers and explosive Linse boats. One Royal Navy destroyer escort, was sunk by a human torpedo along with one minesweeper,, and one landing craft by the German motor boats; at a cost of 41 Neger and 22 Linsen craft.[3]