Empire-class battleship

The Empire-Class Battleship is a battleship type utilized by the Fire Nation Navy. It is a very large ship type, with thousands of crew members. Azula mentions this type of ship in "The Beach" as part of a poor attempt to make a joke.

It is possible that the large flagship Admiral Zhao uses during his siege of the Northern Water Tribe capital is in fact an Empire-Class battleship. Zhao's flagship is a mammoth vessel approximately twice the length, width and height of a standard Fire Navy cruiser (the most commonly seen Fire Nation ship type), making it about the size of the largest battleships built by real-world humanity (like the American Iowa-class and Japanese Yamato-class battleships.) This ship has three smoke stacks instead of two, a different and larger conning tower (with several additional large decks at its base) and an ornate gilded rostrum (the bow spike) much like that seen on Azula's royal barge.

Zuko was stowing away on this ship on its trip to the North Pole (The Waterbending Master and Siege of the North, Part 1) with Iroh acting as his inside man under the pretense of being Zhao's adviser. Zhao's flagship was seen being pushed around by the enraged Ocean Spirit, La, when it merged with Aang to be able to exact its revenge for Zhao's murder of its counterpart, Tui. The ship was likely destroyed with the rest of the fleet.

If the Fire Nation Navy follows real-world ship naming conventions, the class is likely named after the first ship to be built of that design, presumably named Empire (or it could use a anthor system based on size design, and weapons).