Try out this strategy if you like, on Continents maps (for early land and late game water exploring) or on Archipelago (all game water exploring) or anything: First take over your own area to build towards Factories, Oil for modern ships etc. In the late game, for a final finishing attack you can build Transports with Paratroopers / other ground unit, Submarines with Tactical Nukes, and some ICBMs in your cities. In the late game if you have enough production, you can invade a large country from the water all in one turn with Subs nuking the coastal city, and then Transports move in one guy and take the city for free. Then if you move a Transport in the city with Paratroopers in it, you can reach to Paradrop next to a city up to 4 tiles away in-land, which you nuke with ICBMs before, instant capture walking in with a Paratrooper. I tried taking on 4 AIs on a continent with Tactical Nukes on Submarines and Transports with Paratroopers, the first turn I had them surrounded with "Special Forces squads" one per city, it worked like a charm. Instantly hit all armies with 2 nukes (you need 2 nukes to kill even huge armies usually, 3 nukes very rarely) and take everything with 1 transport per coastal spot. Of course they can retaliate from in-land cities so theres ICBMs / Paratroopers to get those fast. Unless its high difficulty, they'll probably offer to surrender after the first turn goes by anyway when you can hit everything on the coast and take it instantly. Naval warfare late game is so much faster than land units, I hate having to move a block of units like 1 or 2 tiles at a time when the enemies have Railroads and stuff.. Transports and Subs are quick on water maps and the enemy will not know what is coming until its too late then.