Picture a four-engine bomber skimming below treetop level at highway speeds in the dead of night, navigating along a forest fire break. This is Operation Chastise, the legendary Dam Busters raid, and it begins with an impossible problem: how do you crack a fortified concrete dam when no aircraft exists that can carry a bomb heavy enough to do it?

We trace the wild engineering of inventor Barnes Wallis, from his rejected earthquake bomb to the backspinning bouncing cylinder that skipped over torpedo nets, and follow the men of 617 Squadron through a raid that breached the Mohne and Eder dams. It is a story of brilliant physics, breathtaking nerve, and a devastating human cost that reshaped international law.

• Why dropping a bomb at exactly 240 mph from exactly 60 feet was the only way the weapon, codenamed Upkeep, could work
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