The Battleship is capable of destroying bases that are close to water single-handedly due to their excellent range and damage. Opponents are practically unable to do anything if their base is close to shore and are attacked by a fleet of battleships.
The Battleship can be used to help protect certain naval units and your docks. It should always be with your Oil Boats and Transport Boats, as those naval units have no means of protection.
The Battleship can also easily destroy bases that are too close to the water without losing a single hitpoint.
To be added