Submarine research level 5 is presented as "Coastal Submarines" which is a bit confusing when we are building "Coastal Submarines" already via the level 2 "Early Coastal Submarine" technology. ' Technically it is correct. Even after several games it makes we raise an eyebrow ala Dr McCoy when I'm told the scientists are having problems researching coastal subs (that I'm already building); close to researching coastal subs (that I'm already building) or congratulations you have now researched coastal submarines (that I'm already building)
My recommendation is to change its name to "Improved coastal submarines"
The level 5 does talk about long ranges so it could also be "Lengthened coastal submarines". I like this one the most.
Was going to suggest "Long range coastal submarines" but that causes confusion with the "Long range" of the ship design which the coastal submarines very much are lacking.