Call it a bug/omission/whatever you want, but...
There needs to be class limits for the officers, petty officers, and enlisted seamen. We had this feature in SH3, so why was it taken away in SH4? As it is now, given the right conditions, one can end up with a boat full of nothing but officers and petty officers, with no restrictions whatsoever. Not to mention, the maximum number of crew each boat can carry is off, especially for the S-class boats.
Bug/oversight #2 has to do with the S-class boat's sonar and radar suite. Accoring to
http://www.fleetsubmarine.com/s-class.html , S-class boats were not fitted with sonar nor PPI radar.