World War II: Operation Chastise

Upkeep bomb mounted on a Avro Lancaster. Public Domain

During the early days of World War II, the Royal Air Force's Bomber Command sought to strike at German dams in the Ruhr. Such an attack would damage water and electrical production, as well as inundate large areas of the region.

Conflict & Date

Operation Chastise took place on May 17, 1943, and was part of World War II.

Aircraft & Commanders

  • Wing Commander Guy Gibson
  • 19 aircraft

Operation Chastise Overview

Assessing the feasibility of the mission, it was found that multiple strikes with a high degree of accuracy would be necessary. As these would have to take place against heavy enemy resistance, Bomber Command dismissed the raids as unpractical. Pondering the mission, Barnes Wallis, an aircraft designer at Vickers, devised a different approach to breaching the dams.

While first proposing the use of a 10-ton bomb, Wallis was forced to move on as no aircraft capable carrying such a payload existed. Theorizing that a small charge could break the dams if detonated below the water, he was initially thwarted by the presence of German anti-torpedo nets in the reservoirs. Pushing on with the concept, he began developing a unique, cylindrical bomb designed to skip along the surface of the water before sinking and exploding at the dam's base. To accomplish this, the bomb, designated Upkeep, was spun backward at 500 rpm before being dropped from low altitude.

Striking the dam, the bomb's spin would let it roll down the face before exploding underwater. Wallis' idea was put forward to Bomber Command and after several conferences were accepted on February 26, 1943. While Wallis' team worked to perfect the Upkeep bomb design, Bomber Command assigned the mission to 5 Group. For the mission, a new unit, 617 Squadron, was formed with Wing Commander Guy Gibson in command. Based at RAF Scampton, just northwest of Lincoln, Gibson's men were given uniquely modified Avro Lancaster Mk.III bombers.

Dubbed the B Mark III Special (Type 464 Provisioning), 617's Lancasters had much of the armor and defensive armament removed to reduce weight. In addition, the bomb bay doors were taken off to allow the fitting of special crutches to hold and spin the Upkeep bomb. As the mission planning progressed, it was decided to strike the Möhne, Eder, and Sorpe Dams. While Gibson relentlessly trained his crews in low-altitude, night flying, efforts were made to find solutions to two key technical problems.

These were ensuring that the Upkeep bomb was released at a precise altitude and distance from the dam. For the first issue, two lights were mounted under each aircraft such that their beams would converge on the surface of the water then the bomber was at the correct altitude. To judge range, special aiming devices which utilized towers on each dam were built for 617's aircraft. With these problems solved, Gibson's men began test runs over reservoirs around England. Following their final testing, the Upkeep bombs were delivered on May 13, with the goal of Gibson's men conducting the mission four days later.

Flying the Dambuster Mission

Taking off in three groups after dark on May 17, Gibson's crews flew at around 100 feet to evade German radar. On the outbound flight, Gibson's Formation 1, consisting of nine Lancasters, lost an aircraft en route to the Möhne when it was downed by high tension wires. Formation 2 lost all but one of its bombers as it flew towards Sorpe. The last group, Formation 3, served as a reserve force and diverted three aircraft to Sorpe to make up for losses. Arriving at Möhne, Gibson led the attack in and successfully released his bomb.

He was followed by Flight Lieutenant John Hopgood whose bomber was caught in the blast from its bomb and crashed. To support his pilots, Gibson circled back to draw German flak while the others attacked. Following a successful run by Flight Lieutenant Harold Martin, Squadron Leader Henry Young was able to breach the dam. With the Möhne Dam broken, Gibson led the flight to Eder where his three remaining aircraft negotiated tricky terrain to score hits on the dam. The dam was finally opened by Pilot Officer Leslie Knight.

While Formation 1 was achieving success, Formation 2 and its reinforcements continued to struggle. Unlike Möhne and Eder, the Sorpe Dam was earthen rather than masonry. Due to increasing fog and as the dam was undefended, Flight Lieutenant Joseph McCarthy from Formation 2 was able to make ten runs before releasing his bomb. Scoring a hit, the bomb only damaged the crest of the dam. Two aircraft from Formation 3 attacked as well but were unable to inflict substantial damage. The remaining two reserve aircraft were directed to secondary targets at Ennepe and Lister. While Ennepe was unsuccessfully attacked (this aircraft may have struck Bever Dam by mistake), Lister escaped unharmed as Pilot Officer Warner Ottley was downed en route. Two additional aircraft were lost during the return flight.


Operation Chastise cost 617 Squadron eight aircraft as well as 53 killed and 3 captured. The successful attacks on the Möhne and Eder dams released 330 million tons of water into the western Ruhr, reducing water production by 75% and flooding large amounts of farmland. In addition, over 1,600 were killed though many of these were forced laborers from occupied countries and Soviet prisoners of war. While British planners were pleased with the results, they were not long-lasting. By late June, German engineers had fully restored water production and hydroelectric power. Though the military benefit was fleeting, the success of the raids provided a boost to British morale and aided Prime Minister Winston Churchill in negotiations with the United States and the Soviet Union.

For his role in the mission, Gibson was awarded the Victoria Cross while the men of 617 Squadron received a combined five Distinguished Service Orders, ten Distinguished Flying Crosses and four bars, twelve Distinguished Flying Medals, and two Conspicuous Gallantry Medals.

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Your Citation
Hickman, Kennedy. "World War II: Operation Chastise." ThoughtCo, Aug. 26, 2020, Hickman, Kennedy. (2020, August 26). World War II: Operation Chastise. Retrieved from Hickman, Kennedy. "World War II: Operation Chastise." ThoughtCo. (accessed March 21, 2023).