I was sort of hoping for Pirate theme Naval Combat of some sort. Personally, I love the idea of Pirates and Royal Navy-esk struggles for control of the largest piece of land: the Sea. I would share my crappy art to illustrate, but I have no clue how to attach pictures. But basically, this is how it would work: there would be ships with platforms maybe, or platforms built into the sea itself where you could build towers. All ranged towers would be the same, but Barracks would instead be a Dockyard, or something along those lines. There would be different upgrades for the "Barracks" at that point,
maybe "Reinforced Prow" to allow Ships to stun an enemy once before they were boarded. Oh, did I mention? That's how Soldier combat would happen. Boarding enemy vessels. Other upgrade ideas of mine include:
Cannons
Allows the Soldiers to do ranged damage before Boarding. Cannon in itself could have subupgrades like Grape Shot, to reduce enemy crew, and Bollo Shot, to break an enemy mast and make them slower after combat.
Powder Rifle
Allows Soldiers to do a different kind of ranged combat, all targeting enemy crew. It could also have subupgrades like Powder Pistol, allowing Soldiers to whip out a pistol and do additional damage during a Boarding fight every once and awhile.
Cloth Sail
Would allow ships to catch up to enemies faster. Could have subupgrades as well, like Black Sail, which would "scare" the enemy and make Soldiers have a, as an example, 10% chance of winning a Boarding attack without even fighting.
Captain
Would increase Soldier's fighting by a small percent like, lets say, 2% and would put a tough-as-nails Captain with the Soldiers who would be tougher than the average Joe.
Pirate Mercenaries
Would give you one reinforcements worth of extra Soldiers on board all ships from the Dockyard with the upgrade.
Well, that's all for now. Hope I get some "Swashbuckler" sympathy. I'm so funny.