SSN - Nuclear Powered Attack Submarine
Underwater terror... Nuclear-powered attack submarines are unmatched opponents when it comes to attack ships or other submarines. Best way to protect from them is to have one on your side. Nuclear propulsion gives them exceptional endurance under the sea, only limit being crew's tiredness. They can do everything, from anti-ships or anti-subs missions, intel gathering, special forces insertions... They can be at a disadvantage though, when sailing in shallow waters, classic propulsion subs, which are smaller, are a better choice.