Seamonsters by Tony Matthews
Tjis one is an interesting read. It looks at the most infamous submarine commanders in WW2, what war crimes they comitted and how the investigation into those War Crimes went and the subsequent legal ramifications and sentencing.
Some of it can make your stomach turn.
and
probably for the 8th time now
Iron Coffins by Herbert Werner
In my opinion the best but I'm biased because its the first book I ever truly read soon as I was old enough to read beyond Dr Seuess and whatnot. The accounts in this book are visceral and really put you into a claustrophobic inducing tin can at the bottom of the ocean, waiting anxiously for the depth charges to finish.