If anyone is struggling with the strategy of this game (like me) there is a wealth of expertise from one of the other guys in my WB squad board. I'm not sure whether I'm allowed to link to the board from here, but I'll find a way to post it. Some excellent tips about RL UBoat captaincy and techniques, dos and don'ts.
I got frustrated on Single Mission #3 - sink the Courageous. The large carrier is steaming along at 20 knots, and my Uboat can do only 17 knots at surface. The mission starts in broad daylight, and I have no way of knowing how to get in torp range of the target without being detected. I end up being targeted by two destroyers that come at me at 36 knots! I got fed up with that, so I brought the boat around and fired off a torpedo from about 600m range. Much to my surprise, I got a single hit which sank the destroyer. Just at that moment, dinner was ready, so I had to save the game. So...
... can someone tell me how I should resume that game, later on? The intended target was steaming away. I don't know that I can catch it!