It is pretty hard, but once you play enough and learn the moves you'll be a good captain in no time and remember that in sinking a ship and fighting as a U-boat commander, it takes alot of patience, don't rush!
Use every resource that you can and take your time when attacking an enemy ship (making sure you identify that it is one), and until it's bearing, speed, and aob come to you more clearly and you agree with it, fire and see how well you did in calculating.
If you need a good manual, here is one of Wazoo's training manuals to get you started!
http://www.filefront.com/14441309/Wa...nual-v2.3.zip/