We have battleships, big deadly fish, and a literal Kraken, but why not any carriers?
Unlocked at level 60 at the end of a new quest line, the sovereign super carrier would be a new naval boss, serving as a naval equivalent to a Goliath tank in terms of functionality. The super carrier should be facing horizontally on the field and be separated into 3 parts, each with their own attacks, HP pools, resistances, and immunities/weaknesses. Each part should use one of 3 plane types: fighters, dive bombers, and torpedo bombers. If the central part of the carrier (where the island and bridge are located) is destroyed, you win. Otherwise, the battle will continue, similarly to the ancient sentinel or Goliath tank. The HP pool for each individual part would not be higher than a mission dreadnought (so probably no more than 2000 combined HP and armor), with the central body being closer to 3000-3500 HP and armor. Resistances should overall be similar to the dreadnought, but with a higher HP to armor ratio and worse resistances to torpedo and explosive attacks. Damage should be comparable to other naval bosses at this level, but using various different attack patterns, damage types, and DoTs.
Boss drops: the sovereign super carrier should drop a higher amount of steel, gears, and bars than the dreadnought.
The boss drops unit should be a fleet carrier, which would serve as a combination of all 3 parts of the super carrier, having all 3 plane types and many different attack options. In exchange, it should only have 3 attack slots (one for each plane if you want to balance it, or multiple for one type if you are okay with ignoring the others), and should have relatively low resistances and overall survivability, being more of a backline damage dealer.
Credit to @mellow tusk for the base concept.