When war breaks out in 1939, Germany turns to the U-Boat as a weapon meant to starve Britain into surrender, cutting the convoys that carry food, fuel, and troops across the Atlantic. This History Hit film tracks the Battle of the Atlantic from the German side and the British, following how the Kriegsmarine's wolfpack tactics nearly broke the supply lines and how the Royal Navy and RAF Coastal Command fought back with new technology and new thinking. Sonar, radar, and code-breaking at Bletchley Park all get their place in the story, alongside the sheer physical ordeal of serving aboard a U-Boat, cramped, oxygen-starved, and hunted by depth charges for hours at a time. Archival footage of convoys under attack and sinking ships sits alongside expert interviews explaining how the tide turned against the U-Boats by 1943. The film treats the Atlantic campaign as the war's longest continuous battle, one where a single strategic shift in tactics and technology decided whether Britain could keep fighting at all.