I know we're quite a long way off from something like this being implemented in the game, but I figured I would just give my thoughts on how naval warfare could be implemented.
1) Naval damage category would be added (similar to air, ground, infantry, building). Existing units would be given damage amounts for naval units.
2) Maps would contain Naval Starting Hexes - They would look different than the normal starting hexes and only naval units could be built there.
3) New Units
Tanker - This would be the "infantry" of the seas. It can capture resource nodes and control points on the water.
3 Movement, 3 Range, 2 vision, light attack vs ground, air, naval, infantry, building
Cruiser - A fast all purpose ship great at anti air.
4 Movement, 4 range, 3 vision, high attack vs air, medium attack vs ground and naval, light attack vs infantry, building
Battleship - The most powerful ship. Cannot attack air.
2 Movement, 5 range, 2 vision, high attack vs ground and naval, medium attack vs infantry and building
Submarine - Devastating to naval units. Can only be spotted by naval units
Cannot attack air, infantry, building, or ground.
4 Movement, 3 range, 4 vision, high attack vs naval.
4) Cruisers counter air and are reasonably priced. Battleships should own cruisers. Submarines can sneak up on boats since they cant be spotted by air. Air is needed for vision as naval units don't have great vision. Seems fairly balanced.
5) Maps would have to be built around the addition of these new units. Consideration would have to be taken for areas that would be good for naval bombardment.
Anyone have any other ideas? I'm curious what everyone else thinks about this.