Submarine attacks on warships in port

[elxaime]

I'm not sure if this has been brought up elsewhere, but some consideration needs to be given to the current ease by which submarines can attack and destroy ships in port.

Typically, this is accomplished by German U-Boats, who are able to easily sink the Soviet Navy in Leningrad. But you also see it happen against UK vessels, particularly battleships which haven't yet been upgraded. While I understand ships in port were vulnerable to air attack, it seems too easy to destroy or damage them from sea, especially with submarines.