So I'm wondering if anyone can tell me, or can direct me to a resource that can, how to determine the effectiveness of naval armor, ideally from the pre-dreadnought period. Specifically I'm looking for a way to figure out how much protection a given thickness of armor would provide against a given size of shell. i.e 6" of armor will stop a 3" shell at 4000 yards, 4" at 5000 yards and so on.
Thanks in advance,
Jack