The Dambusters Raid

“After me, the flood”

A Lancaster bomber during a 2013 reenactment of a training maneuver for Operation Chastise
(Photo: Air Team Canon)

Operation Chastise, popularly known as the Dambusters Raid, is one of the better-remembered bomber operations of World War II. Using an experimental bomb, heavy bombers of the Royal Air Force struck at several dams in Germany’s industrial heartland on the night of May 16-17, 1943. While the attackers suffered heavy losses, they managed to not only damage the German war industry, but also raise spirits at home, finally giving the Germans some spectacular payback for the Blitz.
 
The Ruhr valley, located near the German-Dutch border, was a center of German coal and steel production – in fact, it’s no accident that France and Belgium occupied the area for two and a half years in the early 1920, or that Hitler re-occupied it with German forces in 1936 in direct violation of the Treaty of Versailles. The Allied nations of World War II were obviously aware of the region’s importance to the German war economy.

Industrial landscape in the Ruhr valley, photographed in 1949 (Photo: Bundesarchiv)
Industrial landscape in the Ruhr valley, photographed in 1949
(Photo: Bundesarchiv)

The idea of bombing dams in the valley to disrupt electricity production and to flood mines and factories was already considered by the British Air Ministry before the war, but they lacked the means to do it. Seen from the air, a dam is a very narrow strip of a target, surrounded by water on both sides. Hitting such a small spot with a sufficiently heavy bomb to cause serious damage was considered beyond the technology of the time. Additionally, some of the Ruhr valley dams were concrete “gravity dams,” which would only take light damage from a direct hit to their top. These could only be seriously breached by an explosion much further down, deep inside the reservoir, which would weaken the structure and allow the reservoir water’s pressure to break through. Such a deep explosion could theoretically be achieved with a torpedo, but the Germans were prepared for such an attack, and had installed torpedo nets across the reservoirs.

Diagram of how the bomb was to be deployed (Image: Imperial War Museums)
Diagram of how the bomb was to be deployed
(Image: Imperial War Museums)

The solution was invented by British aircraft engineer Barnes Neville Wallis. In early 1942, Wallis started experimenting with skipping stones in his garden: flat stones thrown with a spin could make them skip across the water’s surface. He set about designing a bomb that could do the same: it would skip along the surface of the reservoir jumping past the torpedo nets, then come to a stop right at the dam and sink to the appropriate depth before exploding. Originally, he wanted to use such bombs against German battleships, such as the Tirpitz that spent most of the war moored up in Norway, which were similarly protected by torpedo nets; but the idea to use such bombs in the Ruhr reservoirs came pretty quickly.

Barnes Wallis (Photo: unknown photographer)
Barnes Wallis
(Photo: unknown photographer)
Wallis and the engineers cooperating with him on the project proposed three different types of such “bouncing bombs.” The Highball was intended specifically for the Fleet Air Arm for use by carrier-based planes against ships, and looked like a giant golf ball with a spherical shape and pitted surface; tests with this weapon carried on until the end of the war in Europe, but it never saw action. A second type, similar but smaller, was codenamed Baseball and intended to be launched from motor torpedo boats. The third type, and the only one to be used in combat, was Upkeep: a 9,250 lbs (4,200 kg) cylinder that would be powerful enough for use against not only German battleships, but also dams.
Barnes Wallis and others watching a practice version of the Upkeep bomb during a test (Photo: Imperial War Museums)
Barnes Wallis and others watching a practice version of the Upkeep bomb during a test
(Photo: Imperial War Museums)

Testing of the skipping bomb concept began in May 1942. A 1:50 scale model of one of the Ruhr dams was blown up at the Building Research Establishment, followed by the breaching of a disused dam in Wales. Additional trials revealed that the bomb (called a “mine” at the time, even though it was technically a depth charge intended to detonate underwater) had to be dropped under extremely accurate circumstances in order to give the correct number and length of skips before sinking.

The 1:50 scale dam model used for early experiments (Photo: Imperial War Museums)
The 1:50 scale dam model used for early experiments
(Photo: Imperial War Museums)

The plane carrying the bomb had to fly at a speed of exactly 240 mph (390 km/h), 60 ft (18 m) above the water, and release the weapon at a specific distance. Maintaining the correct speed wasn’t too hard, but the other two factors proved trickier. Altimeters work by detecting air pressure, which gets lower the higher you go; but World War II-era devices were not accurate enough to keep a plane 60 ft above the water. This was fixed by mounting two spotlights on the underside of the bombers, one under the nose and the other under the fuselage. These were angled so that the light cones emitted by them intersected each other 60 ft below. If a crewman looked out at the water below while flying at the correct altitude, he would see a single circle of light; flying too high or low would result in two circles.

  Artist’s depiction of a bomb run, showing how the spotlights helped keep the bombers at the correct altitude (Image: Twitter)
Artist’s depiction of a bomb run, showing how the spotlights helped keep the bombers at the correct altitude
(Image: Twitter)
The final problem was determining the correct distance. Two of the targets, the Möhne and Eder dams, each had a pair of small towers built atop them, and the distance between the towers was known. A simple triangular wooden device was built to help the bomb aimer. The user had to close one eye and look through a hole in the center with the other while turning the device toward the dam. The triangle had two prongs at the far end. When the prongs overlapped the two towers in the distance, the plane was at the correct distance. If the towers were seen between the prongs, the plane was still too far; if the towers were seen outside the prongs, it was too late. The device was extremely simple, but several sources claim that tests revealed that it was hard to use due to the constant vibrations of the plane, so several crews replaced it with a similar jury-rigged contraption built out of pencils and string, which they found easier to use.
Photos of one of the original aiming devices. Sources suggest that this very specimen was used aboard the bomber that managed to breach the Möhne dam.
(Photo: breakingthedams.com)
The Avro Lancaster heavy bomber was selected for the mission, as it could accommodate the extremely large and heavy Upkeep bomb – with some modifications. The upper machine gun turret and most of the armor had to be stripped off the planes to lighten the enough, and the bomb bay doors had to be removed so the massive cylinder could fit inside. An electric motor was added and attached to the bomb: its job was to spin up the bomb to a 500 revolutions per minute backspin before release, giving it the necessary skipping characteristics. (Similar backspins are also used in golf, where they make the ball land more predictably and with a lower chance of an unpredictable bounce.)
An Upkeep bomb loaded into a modified Lancaster. You can also see the motor used to spin it up. (Photo: Imperial War Museums)
An Upkeep bomb loaded into a modified Lancaster. You can also see the motor used to spin it up.
(Photo: Imperial War Museums)
Resistance within the Ministry of Aircraft Production and Bomber Command stymied the project, which only got the go-ahead in February 1943. The mission was scheduled for May, when the reservoirs were to hold the most water (and would therefore have the most damage breaches) due to seasonal rains. This left a mere eight weeks to design and build the final version of the bomb, come up with the necessary modification for the Lancasters, and organize the mission. A new squadron was created for the mission, and the haste meant it had to be assembled before the Royal Air Force’s bureaucracy could give it a proper number. Therefore, it was briefly known as Squadron X before receiving its proper name, 617 Squadron.
The air crews of 617 Squadron (Photo: Royal Air Force)
The air crews of 617 Squadron
(Photo: Royal Air Force)
The squadron was led by Wing Commander Guy Gibson. Holding a rank equivalent to a U.S. lieutenant colonel at the young age of 24, Gibson was considered something of a prodigy, but not equally loved by all. His strict adherence to discipline and his disdain toward lower-ranking officers, NCOs and ground crews earned him nicknames such as “the Boy Emperor” and “the Arch-Bastard.” However, he also cultivated an “inner circle” of intensely dedicated officers and was acknowledged as an effective leader.
Guy Gibson (second from left), King George VI (third from left) and two other officers discussing the raid (Photo: Imperial War Museums)
Guy Gibson (second from left), King George VI (third from left) and two other officers discussing the raid
(Photo: Imperial War Museums)
The mission against the dam took place on the night of May 16-17, 1943. The 19 bombers flying on the mission were divided into three formations. The nine planes of Formation No. 1 were to attack the primary target of the Möhne dam, then fly on and drop any leftover bombs on the Eder dam. The five planes of Formation No. 2 were to fly to the continent along a different route and attack the Sorpe dam. The five planes of Formation No. 3 were held in reserve: they were to finish off the main dams if needed, or attack some smaller ones designated as secondary targets in the area.
 
Formation No. 2 was the first to take off, at 21:28 on May 16. One of the planes, piloted by Flight Lieutenant Joe McCarthy, a U.S. citizen serving with the Royal Canadian Air Force, developed a coolant leak, and the crew only took off 34 minutes late in a spare plane. Formation No. 1 started taking off at 21:39, and the reserves nine minutes after midnight. The planes all kept to altitudes below 100 ft (30 m) to avoid detection by radar; one particular bomber flew part of its route down a firebreak in a forest, staying below treetop level.
Joe McCarthy (left), the American pilot flying in Canadian colors, with King George VI and Guy Gibson (Photo: Imperial War Museums)
Joe McCarthy (left), the American pilot flying in Canadian colors, with King George VI and Guy Gibson
(Photo: Imperial War Museums) 
Formation No. 2 fared poorly. One plane flew over a heavily fortified island by the Germans and was shot down. A second one flew into the range of an uncharted anti-aircraft emplacement, was hit, and had to turn back. A third flew so low above the sea that it actually clipped the water, the collision ripping the bomb off and partially flooding the plane; the plane managed to recover, but had to head home as it had lost its bomb. The fourth ran into some power cables and crashed. Only a single plane of the formation reached the Sorpe dam: the spare bomber McCarthy’s crew took off with.
 
The Sorpe dam was special in that it was not a concrete gravity dam, but rather a massive earthen structure, which could not be breached by dropping a bomb into the water. Instead, Formation No. 2 planned to approach it lengthwise rather than at a right angle, and drop the bombs on top of it. Once McCarthy reached the dam, he discovered that a hill he had to crest on the approach had a particularly high-steepled church atop it, which got hopelessly in the way. Maneuvering over the church and then pulling up before hitting the other hill on the far side of the dam gave the bomb aimer insufficient time to aim. McCarthy made nine “practice” runs at the targets, always wheeling back around, until the bomb aimer finally dropped the payload on the 10th attempt. To the crew’s chagrin, the bomb only caused light damage.
Gibson (on the ladder) and his crew preparing to take off for Operation Chastise (Photo: Imperial War Museums)
Gibson (on the ladder) and his crew preparing to take off for Operation Chastise
(Photo: Imperial War Museums)
The prisoners were safe, saved by an unlikely coalition of Americans and Germans. Some sources claim that several of the German defenders were killed, while others only name a single dead. That dead, however, was Major Gangl himself. During the battle, he saw Reynaud manning a machine gun with great enthusiasm but little tactical sense, in a very exposed area. Gangl was crossing the courtyard to get him to safety when a German sniper killed him. Gangl became an Austrian national hero, and a street in Wörgl was named after him. His men were taken to a prisoner-of-war camp but released soon after. 1st Lieutenant Lee was promoted to Captain and decorated with the Distinguished Service Cross. Kurt-Siegfried Schrader was arrested and imprisoned for his role in the SS, but was released two years later, partially due to his actions at Castle Itter.
The breach in the Möhne dam, photographed the day after the raid. You can see the two structures on the top used by the bombers to gauge the correct distance. (Photo: Flying Officer Jerry Fray, Royal Air Force)
The breach in the Möhne dam, photographed the day after the raid. You can see the two structures on the top used by the bombers to gauge the correct distance.
(Photo: Flying Officer Jerry Fray, Royal Air Force)
The Eder dam was unprotected, as the Germans thought that the shape of the valley made any attack runs on it impossible. While flak fire was not a concern, the hills surrounding the reservoir and the thick fog over the water did pose a serious danger. The first bomber to approach made six runs, always pulling out without getting a good bead on the target, then deciding to take a break while someone else tried. The second bomber struck the top of the dam and seriously damaged itself with the explosion of its own bomb. The first bomber than went in for a seventh attempt and hit the dam, but failed to breach it. The third and last plane still carrying a bomb made one final attempt, scored a perfect hit and breached the target.
The Eder dam, photographed the day after the raid (Photo: Bundesarchiv)
The Eder dam, photographed the day after the raid
(Photo: Bundesarchiv)
Two dams were down, and Formation No. 3 was still ready to attack. One plane was shot down on the way and one got hopelessly lost in the fog before giving up and returning the England, but the last three bombers of the operation eventually reached the same earthwork Sorpe dam that McCarthy hit but failed to seriously damage. The first plane to make an attack run made seven runs, each stymied by the fog. The pilot and the bomb aimer eventually decided to drop incendiary bombs on both sides of the valley. This started a fire whose heat lifted the fog sufficiently to make the dam visible. The bomb hit the dam on the eighth run, but just like McCarthy’s attack before, failed to cause significant damage. The last two armed Lancasters were directed to drop their bombs on two other dams in the region, but one of the two was shot down on the way to its target. According to a post-war analysis of the last bomber’s report and relevant documents from the German side, this plane probably got lost in the fog and ended up dropping its bomb not on its assigned dam but another one five miles away. Either way, this final attack was unsuccessful.
Aerial view of the Eder dam after the attack. The reservoir, where the bombers had to approach from, is at the top; you can see how the planes were forced to come in at an angle and make a left turn at the last moment. (Photo: Bomber Command Museum of Canada)
Aerial view of the Eder dam after the attack. The reservoir, where the bombers had to approach from, is at the top; you can see how the planes were forced to come in at an angle and make a left turn at the last moment.
(Photo: Bomber Command Museum of Canada)
Losses for the mission were high, with eight of 19 aircraft lost, and 53 of the 113 participating aircrew killed and three more taken prisoner. While British losses were high, so was the damage caused. The destruction of the Möhne and Eder dams cut electricity to the area for two weeks, significantly reducing coal and ammunition production. The water rushing through the two breached dams flooded several mines, damaged or destroyed 125 factories, and washed away 25 roads, bridges and railways. Some flooded arable land remained unusable until the 1950s, and repairing the damage forced the Germans to divert workers and resources that otherwise could have been used in building the Atlantic Wall. It should also be noted that some 1,600 drowned in the massive flood, some 1,000 of whom were prisoners of war (mainly from the Soviet Union) and forced laborers.
The flood 13 miles (21 km) from the Möhne dam after the attack (Photo: Imperial War Museums)
The flood 13 miles (21 km) from the Möhne dam after the attack
(Photo: Imperial War Museums)
The immediate damage was great, but several people, including Wallis and Albert Speer, the German Reich Minister of Armaments and War Production, agreed that Bomber Command missed a major opportunity by not following up on the attack. A few traditional bombing missions against the two dams could have dragged out repair efforts indefinitely. As it were, the British sat by and allowed Germany to fix much of the damage rather quickly.
The Möhne dam after the attack (Photo: Bundesarchiv)
The Möhne dam after the attack
(Photo: Bundesarchiv)
Guy Gibson received the Victoria Cross, the United Kingdom’s highest military decoration, for his role in the mission. He became a star, went on a tour of Canada and the United States, and wrote a book about the raid. He returned flying missions later in the war and died in action in September 1944.
Wallis, who encountered much resistance during his work with the bouncing bomb, saw his idea validated. He gained enough traction that he could develop “earthquake bombs,” extremely heavy bombs dropped with great accuracy that could destroy entire city blocks or hardened underground bunkers and submarine pens. 617 Squadron remained in service and became a specialist in precision bombing with Wallis’s earthquake bombs. The squadron’s first mission became immortalized in its official motto, "Après moi, le déluge," French for “After me, the flood.” (In true British fashion, the adoption of the motto was delayed by protests from the Heralds’ College, who pointed out that the phrase was originally either uttered by French King Louis XV in an “irresponsible context,” or by Madame Pompadour, the king’s official chief courtesan.)
The official badge of No. 617 Squadron. Today, the squadron flies American-made F-35B Lightning stealth combat planes.
The official badge of No. 617 Squadron. Today, the squadron flies American-made F-35B Lightning stealth combat planes.
The 1955 film The Dam Busters became very popular and helped preserve the memory of the raid. Interestingly, the Upkeep bombs are depicted as spherical, rather than cylindrical, objects in the movie. This was because several details of the mission, including the bombs’ shape and construction, were still classified at the time. Few people today have seen the film, but many are familiar with some of its visuals indirectly: when George Lucas directed the original Star Wars movie, he based many of the shots of the final attack on the Death Star on extremely similarly composed shots in the 1955 war film.
A comparison of The Dam Busters and Star Wars
(Original footage: Associated British Picture Corporation and 20th Century Fox)
 

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D-Day festivities in Normandy
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