Many thanks, Webster! Good to see that I am not alone.
I gonna check if setting my GPU quality controls to max in the Windows control panel changes anything. But I too have the feeling that it is hard coded that way. And I understand that they most likely did it for performance reasons. Still it is sad, because the harbors are so nice and detailed... What a waste that one can't see them properly.
As a solution I enabled the free camera for my careers and now take a quick look at the harbor area around the target ships BEFORE I launch any torpedoes. Fair enough imo.
Traveling all those thousands of miles in the game to shot my last torps into an invisible wall was very frustrating to say the least...