So I was thinking about ship classifications, comparing them to the ones in Rule the Waves 2, another game about designing ships.
In Rule the Waves 2, the player designs ships between 1900 and around 1960. A battleship, regardless of when built, will always be a battleship because the game defines ships by guns and armor. Battleships have large guns and thick armor. Larger ships with larger guns and thicker armor will be built, but that battleship will never downgrade to a cruiser (well, not unless it was a marginal battleship to begin with, then it might fall down to a heavy cruiser, although it would probably be too slow).
Classifying ships by gun caliber doesn't work in Aurora because the player only starts with the smallest of gun calibers, and researches bigger ones as the game progresses. The difference between say a 2" gun and a 12" gun, both commonly available in early 1990s, are reflected in Aurora as the very beginning and very end of the research tree.
However, armor is an effective and lasting way to classify ships, because the armor in Aurora is reflected in mostly the same way as Rule the Waves 2 and historically. Each level of armor is an improvement because it is less "bulky". Armor 1 is still armor 1, and Armor 12 is still armor 12, its just how much of the ship is taken up by the armor. So, for example the terms Destroyer (ship without/minimal armor), Cruiser (average armor), and Battleship (thick armor) are still applicable, and the Aurora versions could have a lot in common with their historical counterparts. A destroyer might very well be a smaller ship that maximizes its offensive potential by carrying minimal armor, and trade high speed for low range/reliability. A cruiser would probably be the most balanced craft. A battleship would be armor and guns.
...but if the ship classifications are based upon armor, battlecruisers become just as made up as they were historically.