As of now, Battleships are only available to the British and Spanish via cards. This could be expanded and extended to the other factions by the introduction of the Drydock building as a way to train them.
An Age 4 card that sends a Drydock wagon could replace the Infinite 1 Battleship card. Drydocks could act as a Dock on steroids that heals and trains faster and can also train Battleships. Drydocks would be irreplaceable late game building like Factories and would provide an avenue to replace sunk Battleships. It would reuse the Drydock model from the campaigns. It could also have some upgrades for late game water.
Some possible upgrades could be:
Ship Breakers - Allows fishing boats to be garrisoned in Drydocks and recycled to return their cost
Fisheries - Ships a school of fish to your water shipment point
Whalers - Ships a whale to your water shipment point
Europeans, Americans, and Mexicans could obtain Drydocks through a card. Other civs could have access in other ways.
Portuguese Consulate - Replace Ironclad Shipment with Drydock wagon (possibly make available for China in place of French Consulate)
Greek Shipyards (from House of Phanar) - Sends a Drydock wagon
