War Update

With very few gameplay changes, you could implement armed conflict and invasion (of other islands). A troop transport ship could be just a bunch of steel and a bunch of guns (steel, machine parts, wood). Needs 200 or 500 or whatever dudes, plus combat supplies (Food pack, medical supplies, and ammunition (steel, copper, and gunpowder (sulfur, coal) or smokeless powder (wood, steam).
Ground combat could happen on the same screen as ship combat. Superior naval gunfire reduces casualties.
Transports could be built at the dockyard or implement a shipyard. While I'm here, water trucks - barges - would be nice. Could be built at the same shipyard.
The benefit of conquest would be making trade deals with settlements much more beneficial. Also, world mines are OP right now, there's not much point in exploiting resources on your own island. Making players knock some heads to capture them would balance it.

Also, tier 3 ammunition (for tier 3 supplies) would be a use for the infinities of depleted uranium one ends up with.

Wrong game

"Wrong game" says the guy about the game with the battleship.
It's not the wrong game because you're using industrial processes that I detailed for you to improve production, exactly like the space station.

World mines are not OP - they requires a lot of unity and unless easy difficulty is selected, then they are limited (except for a few). I consider enemy ships just a pirates and i would not like to see another war when humanity extinction is at hand (i expect some disaster happened).
How it even differs from sending construction parts to renew/upgrade mines and increase diplomacy with settlements? Just different resources.
Also in the early game having a few hundreds of workers surplus is not much a thing - you need those home.
Local transort ships are long requested, but they would not be that easy - they would require own pathing system and cheks for enough deep water levels. And they would need to be big with enough transport capacity.

There is suggestion under consideration for Procedural map generation. Which I do think would be an awesome addition to the game. To allow us to expand.
Right now, the game is lacking a challenge outside of just building your empire. We have an infrastructure industry, but we all know that the back bone of infrastructure industry is a war industry.
Not so much that we must have war but it would be nice to have the ability to create arms. One so that our ship does not have infinite ammo. But maybe also have ship building so we can make a fleet. Maybe even have and airplanes to have a carrier. Or cargo planes for transport to far cities for trade along with the trains.
Now, not saying we must go to war. But it would be something to where we can work on building a world were we could if needed defend ourself. But if we had procedural worlds eventually it would stand that we would run into someone that would see our expansion as a threat.

Hell Na bro. One Thing im not into is a force pushing me into defense system when i try to enjoy a game. I would rather stop playin then going through that