Type 205 submarine

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.

The Type 205 was in service with the Royal Danish Navy until 2004, in which it was known as Narhvalen class. The Danish boats differed slightly from the German ones to meet special Danish demands.

List of boats
These last two boats were built by the Howaldtswerke, in Denmark at The Naval Dockyard, Copenhagen.

Notes:
 * U-1 and U-2 were originally built as Type 201 submarines with pressure hulls made of non-magnetic steel, but were rebuilt as Type 205 with new pressure hulls out of normal steel after corrosion problems and small cracks were detected.
 * U-1 was given back to Nordseewerke and was used to test an experimental closed-cycle diesel air-independent propulsion system before being scrapped
 * U-11 was transformed to a Type 205A double-hulled boat (the outer hull filled with polystyrene foam to make it unsinkable) and used as torpedo target
 * U-12 was used for sonar trials as Type 205B