I've raided scapa once (i'll never do it again......) in Nov. 39' and I sunk HMS Illustrious

. The trick of gettin out was stay perpendicular to the shore at P/S depth, when a DD lines you up, (Hard a por or starboard at the last minute) there is a chance that it will run aground

. Off course I raided scapa in a II boat (the best for harbour raiding

)
Just dont do it after 40 (its pretty impregnable then..)
Try these links for info also
http://www.subsim.com/radioroom/show...arbour+raiding
http://www.subsim.com/radioroom/show...arbour+raiding
http://www.subsim.com/radioroom/show...arbour+raiding