I think a new gametype should be implemented in addition to global war. Perhaps a map with less players in each game with each player starting on their own small island. As you expand your city and grow the need for more resources you need to plunder and take over new islands (player-held and rebel-held). I think though with a type of game like this, you would have the need to be able to have supply transports cross the ocean. Maybe have a transport truck travel to a harbor and there it would be converted into a freighter with cargo containers or what have you. But the catch could be you need to hold more than one harbor for this process to work. In closing, I feel the naval units are grossly underutilized because there is currently no immediate call for them, so if your only way to expand territory is to cross an ocean, we may see an increase in those who wish to use ships more than others.