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16-17 May 1943Primary source · 2 sourcesWell documented

617 Squadron breaches the Ruhr dams with a bomb that skips like a stone

Barnes Wallis's bouncing bomb and a purpose-built squadron flood the industrial valley below, at a cost of half the aircrew who flew the mission

On the timeline · around 16-17 May 1943 · The Tide TurnsThe Tide Turns617 Squadron breaches the Ruhr dams with a bomb that skips like a stone1943

Quick facts

Unit
RAF No. 617 Squadron
Commander
Wing Commander Guy Gibson
Weapon designer
Barnes Wallis, Vickers-Armstrong
Date
Night of 16-17 May 1943
Dams breached
Mohne and Eder; Sorpe damaged
RAF losses
8 of 19 Lancasters lost, 53 aircrew killed
Ground casualties
More than 1,300 killed in the flooding

What happened

On the night of 16 May 1943, 19 Lancaster bombers of the newly formed RAF No. 617 Squadron, led by 24-year-old Wing Commander Guy Gibson, took off from RAF Scampton to attack three dams in Germany's Ruhr Valley: the Mohne, Eder, and Sorpe. Each aircraft carried a single cylindrical mine, codenamed Upkeep and designed by engineer Barnes Wallis, that was spun backward before release so it would bounce across the water's surface, roll down the face of the dam, and sink to a set depth before detonating, a mechanism meant to defeat the torpedo nets protecting the dams. Flying at very low altitude to line up the drop, the squadron breached both the Mohne and Eder dams; the Sorpe was damaged but held. Eight of the 19 Lancasters did not return, and 53 aircrew were killed. The flooding below the Mohne dam killed more than 1,300 people, many of them foreign forced laborers and prisoners of war housed in the valley, according to the World History Encyclopedia's account of the raid.

Why it matters

Operation Chastise proved a purpose-engineered weapon could solve a problem conventional bombing could not, breaching reinforced concrete dams that had shrugged off earlier attacks, and it became one of the most publicized bombing raids of the war. Its actual industrial damage to the Ruhr was repaired within months, a gap between propaganda value and lasting military effect that historians still point to when assessing strategic bombing's real impact.

How we know

RAF Museum records of Guy Gibson's squadron and Barnes Wallis's bomb development, together with postwar German damage assessments of the flooded valley, document both the raid's execution and its limited industrial effect.

Sources

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617 Squadron breaches the Ruhr dams with a bomb that skips like a stone · World War II · SourcedStory