That said, harbor raiding in SH3 is rather trivial, provided you can avoid the sub nets and minefields.
The ship AI in ports is abysmal. If you stay close to sea walls more often than not enemy escorts will ram the walls or shore repeatedly until they destroy themselves.
More than once on a lark I have raided a harbor, expending all of my torpedoes, and then backed my sub into a slip and surfaced to pull in my external loads and recharge my air and batteries.
The enemy port may light up like the Forth of July, with sirens wailing, searchlights playing, and guns firing your way, but if you are shrouded by walls you can come away unscathed during the entire operation. I like to imagine the dock crew coming down and gawking at the u-boat reloading its torpedoes in one of their slips while the crew looks up and waves.
You have to watch out, though, that your sub does not drift into an open line of fire, though.
Steve