I always say the same... !!!
Stay away of harbors and well protected bases. and more of the hellīs gate (gibraltar)
They are a very dangerous places full of mines, nets, or in this case concrete blocks
and if the thing is not enough dangerous, there are shallow waters and destroyers with a plenty load of depth charges.
Itīs like a mouse trying to steal some food near of the sleeping cat...
Try to surface and not forget to destroy the enigma machine, code books, and other valuable devices...:hmm:.