I just finished reading Ed Offley's book called Turning the Tide. In it, the author describes how the Allies managed to overcome the German U-Boat wolfpacks in 1943. He does this by examining the differing outcomes of various east- and west-bound convoys in March thru May in that year. As Allied coverage of convoy routes improved and code-breaking got better, so did the protection afforded convoys. Donitz. the admiral in charge, finally admitted the lack of success obtained by the U-Boats. Offley's Epilogue and Appendices alone are worth the price of the book. While I was aware of the high costs paid by the U-Boats in 1943, I did not realize how improvements by the Allies helped. In short, this was a worth-while read.
It is the best and most comprehensive book about turning point of Battle of Atlantic. Vicious and vital convoy battles in April-May 1943 couldn't be covered better.