First of all, the "ship class" you need to use is the one that designates that ship in the game - the ClassName - not the class to which it belonged in real life.
The ClassName for a ship can be found in the .cfg file inside its data\Sea folder. For VonDos' RMS Titanic as provided in WB's mod, the .cfg file looks like this:
[Unit]
ClassName=TIT
UnitType=103
MaxSpeed=23
Length=269
Width=28
Mast=52
Draft=15
Displacement=46328
RenownAwarded=890
[2DCompartments]
UnitPos=50,0,416,28
NbOfComp=4
Name1=Propulsion
Area1=52,0,23,26
Name2=Keel
Area2=150,0,237,7
Name3=Engines Room
Area3=193,9,45,17
Name4=Fuel Bunkers
Area4=163,9,28,17
That first line after [Unit] is what you need to look at with regard to adding the ship to your Ship Names .cfg file. So the ClassName for this ship is TIT. (You would pick
that one.
)
What you want to add to Ship Names is:
[TIT]
0001=RMS Titanic
0002=RMS Olympic
If you like you could also add the lines needed to generate cargo and crew info:
[TIT]
CargoTyp=29
CrewRange=850|870
0001=RMS Titanic
0002=RMS Olympic
The '29' indicates a 'cargo' of passengers; Wikipedia shows a crew of 860 for both the Titanic and a third Olympic-class ship, the Britannic, so that's where I got the crew range. Someone who knows better may have a different suggestion for that, I don't know.
You could in theory also add the Britannic to the list but apparently she never sailed as a passenger liner and went straight into service as a hospital ship in WWI, then was sunk by a mine in 1916. As a hospital ship she wouldn't fit the model for this ship in the game, but in a make-believe world where the Titanic is still available to be sunk by a u-boat in WWII - well, it's up to you. If it were me I'd just list her in a third line as
0003=HMS Britannic
rather than using the more historically accurate 'HMHS' as you wouldn't want to sink an ocean liner and then have it turn up in your logs with a hospital ship designation.
I don't know what display name you've added for the ship in your EnglishNames.cfg, but if you're going to let Commander choose from names other than 'RMS Titanic' for her I would suggest just using
TIT=Olympic class liner
in EnglishNames.cfg, that way you won't have a ship positively IDed by name in the game and then (maybe) given a different name in your patrol log.