The Names : "Hermelin","York" "Roon" and "Hindenburg" are highly questionable for actual "existing paper ships"and possibly just made up by Wargaming or some English publications.
"Ship projects" have only been given Names if those ships are selected for constructing and not for some thought processing in a construction bureau .
The Names "York","Roon" and Hindenburg where used for actually keel layed ships in 1916-18 those ships where assigned to replace ships of the same name which were projected for decommissioning.
Furthermore "Hindenburg" was the Name of the President in Germany in the early 30" so a Ship with "his" Name would have been a Battleship not a cruiser.
"Hermelin" is the type of Name for a small Vessel like a Torpedo Boat not for a Cruiser because Small Cruisers have been and still (Frigates today ) are named after German Cities not Persons or Animals.
So I think that the "single letter" versions of Ship project Names are more likely to be the ones we see in a German Techtree, but simple letter names look stupid or "half done" so I appreciate that Wargaming took some effort to give us Ships with nice even made up Names , or do you rather drive a ship with the name " just P" ? xD
I've done some research and I think you can find those Ships in Erich Groemer's compendium volume 1+2.
