I would go with TMO and RSRD for a time just to knock the barnacles off.
When comfortable go with CapnScurvy'd OTC mod if you're really into manual targeting.
This one is also a very good addition. The Traveller Mod.
http://www.subsim.com/radioroom/showthread.php?t=203542.
This link has a good list for the U Boats.
http://www.subsim.com/radioroom/show...11&postcount=5
Magic