Winston Churchill claimed that the "U-boat peril" was the only thing that ever frightened him during World War II. A formidable foe, the U-boat was developed from a small coastal vessel into a state-of-the-art killer, successfully stalking the high seas picking off merchant convoy ships. It was not until the destroyer escort was introduced, alongside the development of destroyer groups with dedicated anti-submarine tactics, that there was an effective means of defence and attack against the U-boat peril. Gordon Williamson describes the design and development of these two deadly opponents, their strengths and weaknesses and of their tactics, weaponry and training. He provides an insight into the lives of the Allied Navy and Wolf Pack crews as they played their deadly games of cat and mouse on the high seas, gambling not only with their lives but with the fate of their nations.