Had a similar experience in heavy fog south of Spain was trying to hunt down what I thought was a single merchant/cargo I had glimpsed through the murk. So I was plowing along on the surface when out of the fog tracers start wizzing past and some rather large pointy shells
ALARM - crash dive, just as im sinking under the waves I spot my attacks through th fog two rather pissed destroyers. The next 45 minutes was a crazy frenzy of dodge weave, depth changing and plugging the leaks those damn pointy shells had made in my boat during the crash dive.
Interesting and rather sobering experience, im guessing the solo ship I thought I had spotted was actually one from the tail end of a convoy
Note to self - use hydrophones more often and heavy fog = bad mmm k