This week in the war, on the night of 16 May 1943 and the early hours of the following day, Lancaster bombers from the RAF’s recently formed 617 Squadron attacked the Möhne, Edersee and Sorpe dams in Germany. The ‘boffin’ providing the technical expertise was Vickers engineer, Barnes Wallis, and the squadron was commanded by Wing Commander Guy Gibson.
Wallis had come up with the idea of breaching the dams, and the idea of doing it by sinking a bomb (in fact a depth charge) in the water alongside the dam wall—which would then crack from the shockwave when the bomb exploded. But how could one deliver a bomb so precisely—particularly when the approaches to the dams were defended by antiaircraft guns and by torpedo nets, positioned in the water?
Wallis’s solution was to design an oil-drum-shaped bomb that would spin as it descended. Each Lancaster would fly low and level and drop its bomb from an exact height, which would be measured by having a pair of searchlights—one in the plane’s nose, one in the tail—cross in an appropriate spot. After release, the bomb would bounce a couple of times on the surface of the water before thumping into the dam wall and sinking. The explosion would be triggered by water pressure.
The Möhne and Edersee were breached. The Sorpe was slightly damaged. Well over a thousand people died, some being civilians, others being prisoners in German P-o-W camps in the valleys below the dams. Fifty-three were from the aircrews of the Lancasters that had taken part.