(As usual, stop me if you've heard this one.) A touch of background if you like: Spoiler : My last war was one where I was basically trying to weaken a rival nation to the point where they lost their vassals. To this end, I used two primary armies. The first invaded enemy territory formerly held by the vassal (with intent to liberate them to one of the vassals once the war was over). The other was essentially a distraction in my rival's main territory. I chose to land my troops near a fort not far from the coast, took it, and used it as a foothold into enemy territory. This was extremely effective, making me an immediate and severe threat that the AI attacked relentlessly. This prevented them from reinforcing the area I was trying to liberate, and was key to the success of the whole campaign. Unfortunately, this incident is isolated in my experience. I don't usually see all that many forts in AI controlled territory. Thus, my suggestion for combat engineers. Essentially a modified worker that can build forts in enemy territory, and possibly other interesting non-combat abilities. For balance purposes, it would need to be limited in some way so that the player(s) can't fort an enemy to death. Fart jokes aside, making it a national unit consumed in the making of the fort would probably fit the bill. This could also be accomplished by normal workers if there was some way to claim a single square of territory with infantry, but the possibilities of a combat engineer unit are far more intriguing.