World War II Day by Day

London, England • May 16, 1943

At least since 1937, two years before the out­break of Euro­pean hosti­lities, British intel­li­gence had looked into devel­oping alter­na­tive ways to destroy German facto­ries in the Ruhr Valley, Germany’s indus­trial heart­land. One sugges­tion was to attack dams in the Ruhr region. The idea was to blow up the dams or strike them with bombs to create breaches that would cause catas­tro­phic flooding. Late on this date, May 16, 1943, a Royal Air Force squad­ron of 19 modi­fied Avro four-engine Lan­caster Mk.III heavy bombers, each with a 9,250‑lb pay­load of one exter­nally mounted, specially designed “bounc­ing bomb” (actually a revolving depth charge code­named Up­keep), flew toward three dams on the Moehne and Eder rivers in the Ruhr Valley.

The “dambusters” in Operation Chastise dropped their bombs into the reser­voirs when spring run­off was at its highest. The barrel-shaped bombs, released with­out the aid of a bomb­sight or altim­e­ter from a height of 60 ft—this while traveling at 220 mph—skipped across the water’s sur­face like stones rico­cheting across a lake, to sink and deto­nate against the face of the dam at a pre­de­fined depth. (Fitted with elec­tric motors to set them spinning back­wards to the direc­tion of travel before being released, the bombs needed to skip over the water to avoid being trapped in pro­tec­tive anti­torpedo steel netting near the wall; spinning back­wards ensured that the bombs hugged the wall when they hit it and sank.) Three hydro­static fuses deto­nated the thin-skinned bombs some 30 ft below the sur­face and the shock waves of 6,600 lb of Torpex explo­sive (50 per­cent more powerful than TNT by mass) punched huge holes in the dams, causing large portions of the walls to collapse.

The spectacular feat of precision bombing, arguably the most auda­cious bombing raid of the Euro­pean war, breached two of the three tar­geted dams. The Moehne dam alone spilled around 330 mil­lion tons of water (87 per­cent of its reser­voir) into the west­ern Ruhr region, devas­tating fac­tories, homes, mines, bridges, roads, pumping stations, and farm­land for miles around. Some farm­land remained effec­tively un­us­able until the 1950s. The loss of the two dam power plants and the destruc­tion of seven others inter­rupted hydro­electric power gene­ration for about two weeks. The greatest im­pact was felt, as intended, on the Ruhr’s muni­tions indus­try. German leader Adolf Hitler dispatched 7,000 workers to clean up the damage and begin rebuilding the dams. He also approved the trans­fer of an addi­tional 20,000 workers, many from Atlantic Wall projects, to assist with the dam repairs, which were com­pleted five months later for a loss of as little as 5 per­cent of arma­ment pro­duc­tion in the latter half of 1943. Strangely, the RAF, at a cost of 8 Lan­casters and 53 crew members in the Chas­tise raid, did not return to bomb the dams as they underwent repairs.

Bodies of at least 1,579 vic­tims were found along the Moehne and Ruhr rivers, with hun­dreds of people gone missing. The city of Neheim was worst hit: over 800 people perished, among them some 500 female slave laborers from the Soviet Union. The drowning of thou­sands of civil­ians and POWs led to changes in the Geneva Con­ven­tion to pro­hibit simi­lar raids in the future “if such may cause release of dan­gerous forces from the works or instal­la­tions and consequent severe losses on the civilian population.”

Operation Chastise: Busting Dams in Germany’s Industrial Heartland

Left: A practice 10,000-lb barrel-shaped bouncing bomb attached by V‑shaped cali­per arms to the bomb bay area of Wing Com­mander Guy Gibson’s Avro Lan­caster, at Manston, Kent, while conducting dropping trials at the Reculver bombing range. To reduce weight and drag, the Lan­caster’s mid-upper gun tur­ret was removed, the hole covered, and the bomb bay doors removed. The deficit of a missing bomb­sight was made up by hand-held, trian­gu­lar pieces of wood with a sighting hole at the apex. The oppo­site base had nails in various points that when lined up with the dam’s two sluice towers fixed the release point for the bomb. Determining the 60‑ft height on account of the missing altim­eter were two angled Aldis spot­lights, one installed in the nose and the other behind the bomb bay to create a figure eight pattern that could be seen by the bombardier in front of the starboard wing.

Right: Movie still, showing an inert, practice version of the bouncing bomb being dropped during a training flight by members of RAF 617 Squa­dron at Reculver bombing range, Kent. The bomb’s ingenious designer, Barnes Wallis, and others watch the practice bomb strike the shoreline.

Left: The Moehne dam breached, photo­graphed by an RAF pilot on May 17, 1943, one day after RAF 617 Squad­ron had attacked the dam with their cylin­dri­cal bombs. Six bar­rage bal­loons can be seen above the dam. The two direct hits on the con­crete-and-steel gra­vity Moehne dam resulted in a breach around 250 ft wide and 292 ft deep. A tor­rent of water around 32‑1/2 ft high and traveling at around 15 mph swept through the valleys of the Moehne and Ruhr rivers in North Rhine-West­phalia, extending for around 50 miles from the source.

Right: After numerous runs along the length of the Eder dam, the largest in Europe, the Chastise Lan­cas­ters managed to breach the dam in two places, causing the dam to release 75 per­cent of its con­tents. The wave from the breach was not strong enough to result in sig­nif­i­cant damage by the time it reached Kassel, the largest city in North­ern Hessen, some 22 miles down­stream. The crest of a third dam, the Sorpe dam, had a por­tion blown off—this after 10 runs—but was other­wise un­scathed, pro­tected from the Lan­cas­ters by an increasingly dense fog that rolled in during the raid.

Dambusters Declassified Documentary: Retracing the Legendary 1943 Raid by RAF 617 Squadron