I created this simple mod that turns Armstrong gun cannonballs into miniature nukes. These cannonballs have 200 speed, 200 damage and and an explosive radius of 200. They are obviously overpowered, so I don't expect many people would want to use these units in a campaign. On the other hand, the AI can use these units, so it might make the late game kind of interesting.
Now watch these guns decimate Tarajo Castle:
ArmstrongNukeArtillery.zip