There is one more element that i almost forgot to add from my earlier post, in listening to some of these quote's from actual patrol's, the missing element i think that most of you are forgetting is delection angle. Whether a ship is armored or not doesnt have as much impact as to WERE the armor is located, and at what deflection the round is impacting. The bottom line is there is no set formula as to how many rounds on average it would take to cause catastrophic damage to a MERCHANT ship. There are just way too many variables involved, The ship that was some 8000tons might of only taken 6-12 rounds to sink because it may have had a extremely long service life which has weakened it superstructure. No one will ever truly know for sure.
