World War II Day by Day

London, England • May 16, 1943

At least since 1937, 2 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 4‑engine Lan­caster Mk.III heavy bombers, each with a 9,250 lb./­4,196 kilo­grams pay­load of 1 exter­nally mounted, specially designed “bounc­ing bomb” (actually a revolving depth charge code­named Up­keep), flew toward 3 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 feet—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 feet/­9.1 meters below the sur­face and the shock waves of 6,600 lb/­2,994 kilo­grams 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 2 of the 3 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/­kilo­meters around. Some farm­land remained effec­tively un­us­able until the 1950s. The loss of the 2 dam power plants and the destruc­tion of 7 others inter­rupted hydro­electric power gene­ration for about 2 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 5 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./­4,536 kilogram 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. Only 1 test with a live bomb ever took place, this 3 days before Oper­a­tion Chas­tise kicked off. 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 2 sluice towers fixed the release point for the bomb. Determining the 60 ft. height on account of the missing altim­eter were 2 angled Aldis spot­lights, 1 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, 1 day after RAF 617 Squad­ron had attacked the dam with their cylin­dri­cal bombs. Six bar­rage bal­loons can be seen above the dam. The 2 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 32½ 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/­80 kilometers 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 2 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/­35 kilo­meters 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