Winston Churchill claimed the ‘U-boat peril’ was the only thing that frightened him during World War II. The U-boat was developed from a small coastal vessel into a state-of-the-art killer, stalking the high seas picking off merchant convoys, until the introduction of the destroyer escort, and the development of dedicated anti-submarine tactics provided a means of defence and attack against the U-boats. Gordon Williamson describes the design and development of these two deadly opponents, their tactics, strengths and weaknesses, weaponry and training. He provides an insight into the lives of the Royal Navy and Wolf Pack crews as they played their deadly games of cat and mouse on the high seas, gambling with their lives and the fate of the nations.