Now your sub can sustain any non-lethal damage and provided that it has enough of replacement parts return to 100% health at see. This is completely unrealistic since not any damage could be repared during patrol. I propose to write scripts that model variation of hull integrity according to damage from DC's. The integrity level is invisible, but it affects crash depth: more damage -> less integrity -> lower maximum depth that sub can safely dive. Damage accumulation can be tracked as sum of local problems: minor from light bulb crash, more from system failures and major from leaks.