Bretonia Here the idea is historic knights/paladins. Charlemagne's order is considered the original, Pendragon is from King Arthur's last name, and Durendal, the sword of Roland. (Though Durendal would be badass for a Rheinland ship name too.) I tried to pick names that make you think of Knights, and royalty.
Kusari These names are based on various Asian dynasties. Yuan from China, Joseon from Korea, and Azuchi from AzuchiMomoyama from Japan. Chakri is from Thailand, and is the name of the current royal ruling house.
Gunboat - Chakri
Cruiser that pretends to be a gunboat - Yuan
Battlecruiser - Joseon
Battleship - Azuchi
Rheinland For this, I continued the idea of Norse and Teutonic gods.
Gunboat - Baldur
Cruiser - Woden
Battleship - Freyja
And that's it for now I guess... If there's any comments, corrections, etc. I welcome them!