I was doing some testing tonight and I am cough cough uhm cough thinking it may be ok cough.

I noticed that when I set my self up so that I received damage which left me with 71% hull integrity, I then at a depth of 50 metres ensured that the AI would know where I am.

I received a volly of about 16!! depth charges along my course at about the right depth. The depth charges exploded left, right, on top of me etc and I ended up with a LOT of damage and severe leaking but the hull integrity remained at 71%. I died from flooding.

The u-boat looked like it was ducking and weaving as the depth charges exploded all around and on the u-boat.

Further testing will see if this was a "feature" or a good damage model.