During the Second World War, the German Navy created a special K-Verbände (K-Verbände, full name Kleinkampfverbände der Kriegsmarine). Its tasks were to conduct sabotage and assault operations on rivers, at sea and in the coastal zone. The unit consisted of units of subversive boats, manned torpedoes, combat swimmers and various types of mini-submarines. One of these submarines was the single-seat ‘Molch’, designed for operations in the coastal zone. They were equipped with a single electric motor for surface and underwater propulsion, a submersible depth of up to 60 metres, and a maximum speed of 5 knots in the underwater position.

The Molch was built at the Deschhimag shipyard in Bremen, with a total of 393 Kriegsmarine units.  These submarines were deployed in the Mediterranean and North Seas as part of Compound K. Another type was the ‘Seehund’, which was larger, had improved seaworthiness and a two-man crew. They also had two separate engines for surface and submarine operations. By the end of the war, 285 units had been built, and they were considered the best type of German ultra-small submarine. After the war, several Seehunds served in the French Navy.