In the third season, a group of young submarine crew members find themselves in the midst of the turbulent Battle of the Atlantic. Their journey is accompanied by the relentless pursuit of a Royal Navy Commander (played by Ray Stevenson) who becomes obsessed with tracking them down. As they face the perils of war, they are assigned a treacherous mission that takes them to the unpredictable waters of the Southern Hemisphere. United under the leadership of Robert Ehrenberg (portrayed by Franz Dinda), the crew forges strong personal bonds that will be tested to their limits.