I managed a successful raid on Gibralter once. Took my Typ VIIB into the port and managed to get over the sub net. Used all of my torpedos and sank almost every docked merchant. Leaving was a challenge since to get back over the net I had to go decks awash. Whole crew survived with only moderate damage!
I'm actually overdue for another good harbor raid. Might stir the pot at Valletta and see if I survive.