Not so fast ....
While I have no idea if the NF developers based their Kaiser BB6 design on anything other then their own whim there is some historical basis for this ship design.
nazi Germany developed their navel development project named "Z Plan" in 1938 for developing a fleet to dominate the seas.
As WWII started and progressed this plan was modified many times. Various iterations of the Z plan did include paper plans for both an "H" and "J" battleship variants armed with 16" guns with displacements of 83,000 tons and up. These two ships designs progressed to the point that they were actually laid down in 1940 and also subsequently canceled the same year as war priorities forced changes in materials allocations. So the "H" and "J" ships at least qualify as a "real" ship in one sense.
Back to the specific question on the BB6. There were plans drawn up between 1942 and 1944 that did in fact, on paper, reference a ship weighing in at 122,000 tonnes mounting an eight 20" gun main armament. These ships were to be powered by 12 diesel motors powering three propeller shafts. These plans never made it to actual production. In the words of one British navel architect who reviewed the captured plans post war the nazi ship design staff seemed "intent on avoiding service on the eastern front by showing their bosses how busy they were." So the "Kaiser" BB6 does get the rating of "paper ship" as does the Montana.
So there you have it. There is in fact some historical basis for three of the post Bismark nazi ship designs included in Navyfield.
Sorry about the text color.