I seem to never get hit at 30-feet i dont know why but, they either set charges to periscope or around 50 feet or deeper but never 30. once i had 2 destoryers after me, i stayed at 30 at slow-speed and went to external view and watch where they dropped them, always above or below but never on target i was always allowed to slip away
Dont know if this is a bug or thats how they did it back then.