I'm not totally sure, but this would be the real world classification: Frigate, Corvette, Destroyer, Cruiser, Battlecruiser, Dreadnought, Battleship. Keep in mind that Battlecruisers, Dreadnoughts and Battleships became obsolete after WWII due to the superiority of naval aircrafts (example: 2 of 3 Italians battleships were destroyed by English Swordfish in the Taranto harbour, the Bismarck was almost disabled by a wing of Swordfish, then the attack on Pearl Harbour, and the sinkings of the Tirpitz and the Yamato, all by naval aircrafts).
Obviously, there is always the exception: the US Navy used Iowa-class battleships even during the Gulf War.