I recommend that you get the "U-boat Commanders Handbook" (Reprint) from Amazon.com for $ 8.95 if you want to get into the nuts and bolts of attack planning and plotting on German WW2 U-boats. The English version of the handbook has all the answers, procedures and, more importantly for all non-German speakers: the (mostly) correct translation into English of the terminology for U-boat seamanship and weapons (torpedo) use.