[RustySubmarine]

Done a bit of mooching around harbours myself. Have you tried Scapa! Use the far north passage, and start your entry as night falls, you can sneak in so far on the surface, but avoid nights when the moon is out. Be careful as you enter the main area at the end of the channel, as there are some blockade ships, you need to keep mid channel. As soon as you clear these, submerge to periscope depth and rig for silent running. There are a few Destroyers patrolling, but these will anchor around 11pm - midnight and you can pick one of these off with a fish from your stern tube on your way out. There is usually a couple of Capital ships anchored and a few Merchants for the picking, but take the BBs, Cruisers or AC (if you are lucky) I sunk HMS Glorious with HMS Renown when I was there. Keep silent running on all the time, until you clear the main area and enter the channel you came in at. you can clear the blockade ships submerged, but keep mid channel or you will run aground if to close to shore (there are no nets or mines in the channel (or there wasn't in early 1940 when I sneaked in) You should get out of the northern channel by about 6am, but be careful, keep submerged as you will have two or three destroyers hunting you until you can shake them off. Go deep when in deeper water and just sit it out until they call it a day. Then you can surface when all is clear. Worked ok for me!