Since starting this game i have found my book collection(with regard to u-boat warfare) has grown exponetianallyincluding u-boat ace(specifically because he operated off cape Town).Some others that i heartily recommend:
Ten years and Twenty days, the memoiors of karl Doenitz.written after his release from Spandau, if focuses nearly entirly on the u-boat campain.It is brilliantallowing us insight into things like the laconia incident etc.A must have.
TEDDY SUHREN - ACE OF ACES. A good book but the translation from German doesn't make for very smooth reading, but if you go for it get the next reccomendation as well.A good couple of laughs from a rebel submariner.
U-Boat war Patrol-a hidden photographic diary of U564,this book follows one patrol of U564 captained by Teddy Suhren, when they had a photographer on board.The photo's were presumed destroyed during the evcuation of the French bases but were re-discovered in an attic in England 60 years later-where they were placed after being "libereated".The collection has now been published.The photographs and co.mmentayy really give on a feel for life on a u-boat, warts 'n all.
These you should be able to get quite readily, and after reading them one has a much greater appreciation for the game.