How to kill a U-Boat? The threat of the elusive and nearly undetectable submarines had been on the mind of every Allied naval planner since the Great War. As the Kriegsmarine once more unleashed its wolfpacks to the high seas, it became a race against time to find a way to stop the deadly stalkers from beneath the surface.

The thousand-bomber offensive was about to begin as Air-Marshall Harris was assembling his forces. Yet one man was to challenge his strategy. The aircraft designer Barnes Wallis thought: "What if there was a way to destroy Germany's industrial might not by simply dropping thousands of bombs over its cities, but by a precision strike against its dams?" For this, a new kind of bouncing bomb was to be delivered.