Second, if you can read between the lines, this book will reveal the personality of one of the mightiest leaders of WWII. Was he a war criminal? Maybe, but certainly his biggest crime was to be a soldier (with very limited horizon apart from his daily duty) who happened to fight on the wrong side. Bad luck, for both sides...
This book certainly doesn't replace other narratives about the "Atlantic War", but it supplements all of them. Only here, you can find the background story.
If you're looking for more WWII memoirs, try Doenitz' superior, Raeder, and DON'T OVERLOOK Churchill, as he was the greatest writer among all of them.
If you still have no idea as to who Doenitz might have been, then try to read Lothar Guenther Buchheim's vivid picture about how the submariners themselves felt, instead; that is indeed great war literature.