Hey! Definitely try to get a good potential sailor for sonarman (1x) and get some really good +12 or even higher Engineers, one repairman can be useful aswell. Depending of the playstyle SS5 and SS6 you might consider torpedo bomber(s). Level up 2x torpedoman (+11 should be okay). Planesman I personally have just +11. IJN subs are great BB/CV hunters and with a good sonarman, can easily kill other subs from long range. They are slow but if you can work around it - then you are in heven. All the information is from my experience and maybe one calculator boy can add something. Have a great hunt!