The U-boat was a formidable foe, developed from a small coastal vessel into a state-of-the-art killer picking off merchant convoy ships at will. It was not until the destroyer escort was introduced, alongside with dedicated anti-submarine tactics, that there was an effective means of defence and attack against the U-boat. This book describes the design and development of these two deadly opponents, analysing their strengths and weaknesses and assessing their tactics, weaponry and training. Moreover, it is 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 as they gambled not only with their lives but with the fate of the war.