The Rocky — J.E. MacDonnell

Commander Peter Bentley gambled on his hunch about the German raider. Already he’d damaged her, at no small cost to his own destroyer, Wind Rode. Now he was determined to destroy this vicious enemy who preyed on unescorted merchant ships and then vanished mysteriously. It was a daring plan that Bentley conceived … and the success of it depended on the man they called The Rocky.