General gist of the mod: Subs are much more historical. How? Well, they can mess your day up. They can effectively blockade a nation's trade, sink DDs, and capitol ships (provided, they are not escorted by cruisers or destroyers). That sort of thing.
I AM NOT THE CREATOR OF THE ORIGINAL MOD!!!!! If he wants me to remove the mod i will. General gist of the mod: Subs are much more historical. How? Well...