My U-boat was just destroyed in a very disappointing way. I figured I'd share my sad tale...
I had just raided Gibraltar, from the Mediterranean side, and managed to sink a T3 tanker that was anchored in the vicinity of the harbor.

A T2 that was moored in the port didn't sink after 1 torpedo hit...I surfaced to finish it off with the deck gun (no warships were around, by chance) but I had to immediately re-submerge after drawing the fire (and ire) of the many coastal defense guns! (I hadn't noticed they were there!

)
Anyway, my ~50% damaged sub managed to, somehow, slip away. I was almost 'home free', reaching open waters without any warships close by, running at 64x time compression, after a nicely successful patrol. I decided to drop from 20m to 25m just for extra safety...and BAM! The little bit of extra water pressure was enough to destroy the U-boat!

And, running at 64x TC, it happened instantly. (Tip: Don't increase depth with a damaged U-boat except at 1x TC.)
It was a very anti-climactic end to the career.