My observations
 

When the hull of the sub gets damaged you cannot tell how much damage it has until you dive and find out you are dead . The deeper you go the worse the damage gets . I think that the crew on deck are the same . They might be very hurt on deck but you cannot tell until you dive . I changed the crew exposure to 1 in the unitpart upc files and this confirms this . They act exactly the same way as the hull damage .

Wow, I was trying to get AA guns to hurt crew, and had big trouble.

Are you saying ALL hitpoint damage is treated in terms of decreasing crush depth?

tater

Looks to me like this is correct . Might explain some unexplained deaths .