Do not know, what situation does cause your crew death, but about BBs being critical hit (especially from high angle japanesse guns):
1/ Believe armor helps, i have read some threads about it and my experiences confirm this statement. Important is to have "citadel" armored = belt and deck in the same time. So add 0,2-0,4 for the belt and deck (recommend 0,4).
2/ Also high lvl Seaman (above 95-100) seems helps.
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Would say that each precaution can half the number of deaths. (Never regulary tested, but after hundreds of battles doing so...):
- Without armor and Seaman even 15 sailors can be lost in the moment when full high angle salvo land on the ship (e.g. Andrea Doria).
- Now 1 sailor (or 2) once per 3 lost battles, rarely 4 (once per 10 lost battles) die. Sometimes one of those 4 is expert. Believe no veteran died when armor+seaman were implemented (without armor+seaman, veterans die sometimes). Playing KM ships.
Hope it will help you also.