The Type 205 was a class of diesel-electric German hunter-killer U-boat submarines. They were single-hull vessels optimized for the use in the shallow Baltic Sea. The Type 205 is a direct evolution of the Type 201 class with lengthened hull, new machinery and sensors. The biggest difference though is that ST-52 steel is used for the pressure hull since the Type 201's non-magnetic steel proved to be problematic. Type 206, the follow-on class, finally succeeded with non-magnetic steel hulls.
In service with the Danish Navy, the Type 205 is known as Tumleren class. The Danish boats differ slightly from the German ones to meet special Danish demands.