As the Allies pressed forward both in Europe and the Pacific in the waning days of World War II, a little-known battle took place under the frozen seas off the coast of Norway…and changed the course of the war. By February of 1944, both Germany and Japan were falling back under constant attack from Allied forces. The end would have been inevitable, if not for a desperate, audacious plan by the German High Command. The Germans would pack a submarine-boat U-864-with their most advanced rocket and jet aircraft technology, a group of Japanese and German scientists, and tons of mercury for use in missile and torpedo detonation systems. With this, Japan could re-establish air superiority in the Pacific, forcing the Allies to divert troops and material long enough for Germany to re-group and prepare a final defense of the Fatherland. Unknown to them, British codebreakers, working hand-in-hand with the Norwegian underground, had discovered what the Axis powers were up to. Chasing U-864 and her cargo throughout the North Atlantic, the British bombed German naval bases and hidden installations in an attempt to destroy the submarine and her hidden cargo. But in the end, she was able to head out to sea and attempt to complete her mission. The British submarine HMS Venturerwas waiting for her. In a cat-and-mouse silent battle beneath the waves, they hunted one another, each waiting to strike. The Venturerwon the game, sinking U-864 and becoming the only submarine in history to sink another sub in underwater combat. This is the action-packed, dramatic account of one of the unsung greatest victories in military history, and of a historical moment in the annals of naval warfare.