Special ship unit? Does the same thing spies can do? I dunno it seems subs aren't useful unless you change some game mechanics like for example, only allowing spies to see land units,other spies and planes and leaving out ships so the subs can identify ships and destroy them.
I hop because I don't meet the requirements most of the time, and its swell if you've played before. I deleted my original nation to see if I could start out better.