Just a little added history note on the Seeteufel.

Also known as "Elefant" or as Projekt Loedige it was the only advanced midget submarine project to attain actual construction and trials. The need for a tracked vehicle that could launch itself was apparent from the difficulties in getting other midget submarines in the water. Launching locations were usually limited to major ports.
Dipl Ing Alois Loedige, head of the development division at the Kiel/Eckernförde torpedo testing establishment proposed this submarine as a solution.
The first and only prototype to be built was completed in July 1944. It was fitted with an 80hp Opel truck engine although the original design called for a diesel. None of the latter were available.
Trials were held in Eckernförde Bay. The Seeteufel proved capable of 8 knots submerged, 10 kts surfaced and had good maneuverability. On land it proved seriously underpowered and the tracks too small to adequitely support the weight.
The decision was made to build a second prototype (pre-production model) using a 250 hp diesel and a 100 hp electric motor. This model was ordered from the Borgward Car factory at Bremen but was never built. The single existing prototype was blown up to prevent its capture at training camp 'Blaukoppel' outside Lübeck prior to the end of the war.