The Kriegsmarin was just settling on a proper modern stabilized midget submarine at war's end. It sort of resembled the DPRK Yugo class submarine. It was designed to slip throgh a neglected Allied defence window. Luckily for the Allies they had few at war's end and very limited berthing options at the end of the war. Not enough of these made it out of the shipyards. Zeehund iirc.
The Seehund was a fine midget sub for the era, but as is typical with midgets, they lost far more hulls than the ships they managed to sink. Their limited capability would not have served to shift the tide of war, either by virtue of their late appearance (it was nearly 1945) or the fact that they could not hope to intercept the mid Atlantic convoys.






















































