Board Thread:Questions and Answers/@comment-25349773-20141127164836/@comment-25732404-20141129064326

Don't have any difference at all, just the Tsu-Class have a Sonar equipped in her ( Abyssal Sonar Mk II) and a good ASW status,  add it to the good will of RGN-sama and your submarine will easily take considerable damage even in the night. I tried use submarines in E3 and it don't work very well for me too. I gave up and went without them.

Note: It still valid for enemy subs too, with any of your ships have a sonar, depth charge equipped and a good ASW status.