THE BATTLE OF THE ATLANTIC - Andrew Williams

This is interesting but as its an accompaniment to a TV series it is a bit light.  It reads like the voice over the video you would get with the TV show

The author notes at the start that very little has been written about this part of the war and he's right, it would bear a more in-depth study.  There is no way you can cover 5 years off in 200 pages. 

As a brief overview its worth the time.  It has made me want to track down the TV series