After reaching Fortress Level 21, you can obtain the Flagship, Warhorse of Seas, and the Advanced Flagship, Kraken's Wrath. 

The Flagship levels can be increased based on the level of the Flagship Shipyard, a Building that opens after completing the relevant Quest.

As your Flagship level increases, its overall performance improves and you can gain beneficial buffs that support your Expedition Fleet.

* Leveling up the Warhorse of Seas Flagship consumes Warhorse of Seas Blueprints.

Where to obtain Warhorse of Seas Blueprints

- Available as stage rewards on Cannibal Island

- Available as Total Damage milestone rewards from World Boss: Deadly Octopus [Empire] and World Boss: Purgatory Octopus [All Empires]

Where to obtain Kraken's Wrath Blueprints

- Available as Total Damage milestone rewards from World Boss: Purgatory Octopus [All Empires]