The Seehund (or "Seal") was the most successful of the several Nazi Kriegsmarine attempts to perfect a "midget" submarine. Midget submarines were en vogue during World War 2 and attempted by nearly all major powers in the conflict. The inherently small sizes of midget-class submarines made them virtually undetectable to the naked eye of patrols and calculated manuevering by her crews often times allowed such vessels to sneak through mine fields or avoid enemy depth charges. In short, midget submarines could be used in clandestine operations where larger submarines dare not tread. The Seehund became the well-known German submission to this submarine category and saw its origins in 1944. It was also known by its more formal German naval designation of "XXVII B5" as well as "Type 127". However, despite their useful offensive capabilities, Seehunds were utilized in the "Butter Boat" role during the final months of World War 2 - helping to replenish dwindling supplies of those poor German garrison forces stranded along the coasts by the Allied advances inland.
Externally, the Seehund mimicked much of the appearance of their larger submarine brethren. The hull was tubular in shape with a well-pointed bow, bulged sides and a tapered stern. The bow was featureless for the most part while a short conning tower was affixed at amidships and used for entry and exit for the crew. The steering controls were visible to the stern, just aft of the three-bladed propeller assembly. Power was supplied by a single diesel engine developing 60 horsepower. The diesel engine was used to run the boat when along the surface. A separate electric motor was used when the boat was submerged and ran at 25 horsepower. Like other submarines of the time, the Seehund would have to surface to recharge both battery and oxygen supplies and it was during this action that the vessel would be at its most vulnerable.
Seehund midget submarines fielded a displacement of 17 tons when submerged, were crewed by two personnel and were armed with two Type G7e torpedoes. Some Seehund boats had additional fuel storage to provide for ranges in excess of 300 miles. The vessels could reach speeds of 7 knots when surfaced and 3 knots when submerged, the latter ranging out to a limited 63 miles.
Like other midget submarines seeing combat actions in the war, the Seehund proved a successful design and was used throughout some 142 total sorties in the latter months of the conflict. Her class netted some 120,000 tons of Allied shipping sunk across the North Sea. However, that success came at a lethal cost for some 35 Seehund boats were lost in action - most often times to Allied aircraft attack.