IJN SS4 :
its a deadly machine, without rear torps, slow in turning.But good Aimming at MN ss4, will make this guy have a hard time, because you have 8 torpedoes.
Small, 6 front tubes, and 2 rear tubes, makes it very dangerous, for thoses who doesnt have very good accuracy. This little guy can be a pain for most subs, except km.I believe MN torpedoes HITS 1k harder than IJN, Pls correct me if im wrong in the last part, im not sure if im correct. Anyways, this guy can also have a decent or good turning against IJN SS4.
summary: DRIVER makes the difference, doesnt matter what sub you are using.