A little bit of modern German Navy:
The Class 205 U-boats were small submarines, designed for fighting ships in the Baltic Sea. In the last years of their career, two of them were extensively modified:
U-11 was modified into a target ship in the mid-tolate 1980s, reclassified as Class 205A and equipped with a secondary hull.This hull protected her against accidental hits from training torpedoes and in this form she was a unique ship in the NATO forces. U-11 was decomissioned in 2003 and is now a museum ship located in Burgstaaken on the island of Fehmarn.
U-12 was modified in the 1990s as a testbed for new sonar technologies and reclassified as Class 205B. The results and developements tested on U12 were later incorporated into the new Class 212A u-boats. U12 was decomissioned in 2005 and scrapped in 2008.
And who said ramming bows were dead?
Any help and source material is always welcome.