My point was that ships should have no religion and ship shouldn't be the unit that the religion is attempted to inherit from. The current solution will make ship have a religion if you set in XML ship to be free unit in game start. I guess I could make a check that only units able to found a settlement can get a religion promotion. But are all "human" units able to found settlement? How about the list would only contain the religions of your noblemen? They are the ruling class of your society anyway. If you have no noblemen you can't convert to state religion. Or maybe the priests spread their religion if it is also a state religion. Or is that what you meant? If you have no state religion or you run religious tolerance civic, then even non state religions are spreading. I think missionaries should produce convert of their religion. But you should only be able to create missionary of your state religion units. And when you have state religion the immigrating missionaries are always your state religion. Or does the missionary unit get deleted when founding a mission? Then you can't track the religion of the missionary without further coding.