| Operation Chastise | |||||||
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| Part of the Second World War | |||||||
The Möhne dam on the day following the attacks. |
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| Belligerents | |||||||
| United Kingdom | Nazi Germany | ||||||
| Commanders and leaders | |||||||
| Guy Gibson | Josef Kammhuber | ||||||
| Strength | |||||||
| 19 Lancaster bombers | XII. Fliegerkorps (Defending three dams) |
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| Casualties and losses | |||||||
| 8 aircraft shot down, 53 aircrew killed, 3 aircrew taken prisoner. |
2 dams breached, 1 dam lightly damaged, approx. 1,600 killed (including 1,000+ prisoners and forced labourers). |
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Operation Chastise was an attack on German dams carried out on 16–17 May 1943 by Royal Air Force No. 617 Squadron, subsequently known as the "Dambusters", using a specially developed "bouncing bomb" invented and developed by Barnes Wallis. The Möhne and Edersee Dams were breached, causing catastrophic flooding of the Ruhr valley and of villages in the Eder valley, while the Sorpe dam sustained only minor damage.
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Prior to World War II, the British Air Ministry had identified Germany's heavily industrialised Ruhr Valley, and especially its dams, as important strategic targets: in addition to providing hydro-electric power and pure water for steel-making, they also supplied drinking water and water for the canal transport system. The methods used to attack the dams had been carefully worked out. Calculations indicated that repeated air strikes with large bombs could be effective, but required a degree of accuracy which Bomber Command had been unable to attain in the face of enemy defences.
The mission grew out of a concept for a bomb designed by Barnes Wallis and developed by his team at Vickers. Wallis was Assistant Chief Designer at Vickers. He had worked on both the Vickers Wellesley and Vickers Wellington bombers. While working on the Vickers Windsor he had also begun work, with support of the Admiralty on a bomb designed initially for attacking ships though dam-destruction was soon considered.
Wallis' initial idea was to drop a 10 t (9.8 long tons; 11 short tons) bomb from an altitude of about 40,000 ft (12,200 m). This idea was part of the earthquake bomb concept. However, at that time no bomber aircraft was capable of flying at that altitude with such a heavy payload. A much smaller explosive charge would suffice, if it could be exploded directly against the dam wall below the surface of the water, but the major German reservoir dams were protected by heavy torpedo nets to prevent such an attack.
Wallis' breakthrough overcame this. A drum-shaped bomb spinning backwards at over 500 rpm, dropped at a sufficiently low altitude at the correct speed, would skip for a significant distance over the surface of the water in a series of bounces before reaching the dam wall. Its residual spin would run the bomb down the side of the dam to its underwater base. Using a hydrostatic fuse, an accurate drop could bypass the dam's defences and enable the bomb to explode against the dam.
Initial testing of the concept included blowing up a plaster model dam at the Building Research Establishment, Watford in May 1942 and then the breaching of the disused Nant-y-Gro dam in Wales in July 1942. The first full-scale trials were at Chesil Beach in January 1943. This demonstrated that a bomb of sufficient size could be carried by an Avro Lancaster rather than waiting for a larger bomber such as the Windsor to be built. However Air Vice-Marshall Francis Linnell at the Ministry of Aircraft Production thought the work was diverting Wallis from the development of the Windsor. Pressure from Linnell via the chairman of Vickers, Sir Charles Worthington Craven, caused Wallis to resign. Sir Arthur Harris, head of Bomber Command from a briefing by Linnell also opposed the allocation of his bombers. However Wallis had written to an influential intelligence officer, Group Captain Frederick Winterbottom. Winterbottom ensured that the Chief of the Air Staff, Air Chief Marshall Charles Portal heard of the project. Portal saw the film of the Chesil Beach trials and was convinced.[1] Over-riding Harris, Portal ordered on 26 February 1943 that 30 Lancasters were to be allocated to the mission and the target date was set for May, when water levels would be at their highest and breaches in the dams would cause the most damage. With eight weeks to go, the larger bomb, code-named 'Upkeep', that was needed for the mission, and the modifications to the Lancasters had yet to be designed.
The operation was given to No. 5 Group RAF which formed a new squadron to undertake the dams mission. It was initially called Squadron "X", as the speed of its formation outstripped the RAF process for naming squadrons.
Led by 24 year-old Wing Commander Guy Gibson, a veteran of over 170 bombing and night-fighter missions, 21 bomber crews were selected from existing squadrons in 5 Group. These crews included RAF personnel of several different nationalities, as well as members of the Royal Australian Air Force (RAAF), Royal Canadian Air Force (RCAF) and Royal New Zealand Air Force (RNZAF), who were frequently attached to RAF squadrons under the British Commonwealth Air Training Plan. The squadron was based at RAF Scampton, about 5 mi (8 km) north of Lincoln.
The targets selected were the two key dams upstream from the Ruhr industrial area, the Möhne Dam and the Sorpe Dam, with the Eder Dam on the Eder River, which feeds into the Weser, as a secondary target. While the loss of hydroelectric power was important, the loss of water supply to industry, cities, and canals would have greater effect. Also, there was the potential for devastating flooding if the dams broke.
The aircraft were modified Avro Lancaster Mk IIIs, known as B Mark III Special (Type 464 Provisioning).[2] To reduce weight, much of the internal armour was removed, as was the mid-upper machine gun turret. The size of the bomb with its unusual shape meant that the bomb-bay doors had to be removed, and the bomb itself hung, in part, below the fuselage of the aircraft. It was mounted on two crutches, and before dropping it was spun up to speed by an auxiliary motor.[3]
Bombing from an altitude of 60 ft (18 m), at an air speed of 240 mph (390 km/h), and at a pre-selected distance from the target called for expert crews. Intensive night-time and low-altitude flight training began.
There were also technical problems to solve, the first one being to determine when the aircraft was at optimum distance from its target. Both the Möhne and Eder Dams had towers at each end. A special targeting device with two prongs, making the same angle as the two towers at the correct distance from the dam, showed when to release the bomb. (The BBC documentary Dambusters Declassified (2010) stated that the pronged device was not used due to issues related to vibration and that other methods were employed, including a length of string tied in a loop and pulled back centrally to a fixed point in the manner of a catapult.)
The second problem was determining the aircraft's altitude, as the barometric altimeters then in use lacked sufficient accuracy. Two spotlights were mounted, one under the aircraft's nose and the other under the fuselage, so that at the correct height their light beams would converge on the surface of the water. The crews practised at the Eyebrook Reservoir, in the village of Uppingham, Rutland. Abberton Reservoir near Colchester, Derwent Reservoir, and Fleet Lagoon on Chesil Beach. Wallis' bomb itself was first tested at the Elan Valley Reservoirs.
The bombs were delivered to the squadron on 13 May, after the final tests on 29 April. At 1800 on 15 May, at a meeting in Whitworth's house, Gibson and Wallis briefed four key officers: the squadron's two flight commanders, Squadron Leader Henry Maudslay and Sqn Ldr H. M. "Dinghy" Young; Gibson's deputy for the Möhne attack, Fl.Lt. John V.Hopgood and; the squadron bombing leader, Flight Lieutenant Bob Hay. The rest of the crews were told at a series of briefings the following day, which began with a briefing of pilots, navigators and bomb aimers at about midday.
The squadron was divided into three groups.
Formation No. 1 was composed of nine aircraft in three groups: (listed by pilot) Gibson, Hopgood and Flt Lt H. B. "Micky" Martin (an Australian serving in the RAF); Young, Flt Lt David Maltby and Flt Lt Dave Shannon (RAAF), and; Maudslay, Flt Lt Bill Astell and Flying Officer Les Knight (RAAF). Its mission was to attack the Möhne; any aircraft with bombs remaining would then attack the Eder.
Formation No. 2, numbering five aircraft, piloted by Flt Lt Joe McCarthy (an American serving in the RCAF), Pilot Officer Vernon Byers, Flt Lt Bob Barlow (RAAF), P/O Geoff Rice and Flt Lt Les Munro (RNZAF), was to attack the Sorpe.
Formation No. 3 was a mobile reserve consisting of aircraft piloted by Flight Sergeant Cyril Anderson, Flt Sgt Bill Townsend, Flt Sgt Ken Brown (RCAF), P/O Warner Ottley and P/O Lewis Burpee (RCAF), taking off two hours later on 17 May, either to bomb the main dams or smaller secondary target dams at Schwelm, Ennepe and Diemel.
Two crews were unable to make the mission due to illness.
The Operations Room for the mission was at 5 Group Headquarters in St Vincents Hall Grantham, Lincolnshire. The mission codes (transmitted in morse) were: Goner, meaning "bomb dropped"; Nigger, meaning that the Möhne was breached and; Dinghy meaning that the Eder was breached. "Nigger" was the name of Gibson's dog, a black labrador retriever that had been run over and killed on the morning of the attack.[4] "Dinghy" was Young's nickname, a reference to the fact that he had made many forced landings at sea, requiring him to use the rubber dinghies stowed on RAF aircraft.
The aircraft used two routes, carefully avoiding known concentrations of German anti-aircraft flak, and were timed to cross the enemy coast simultaneously. The first aircraft, those of Formation No. 2 and heading for the longer, northern route, took off at 21:28.[5] McCarthy's bomber had a hydraulics problem, and he took off in a reserve craft 20 minutes late.
Formation No. 1 took off in groups of three at 10 minute intervals beginning at 21:39.[5] The reserve formation did not begin taking off until 00:09 on 17 May.[5]
Formation No. 1 entered continental Europe between Walcheren and Schouwen, flew over the Netherlands, skirted the airbases at Gilze-Rijen and Eindhoven, curved around the Ruhr defences, and turned north to avoid Hamm before turning south to head for the Möhne River. Formation No. 2 flew further north, cutting over Vlieland and crossing the IJsselmeer before joining the first route near Wesel and then flying south beyond the Möhne to the Sorpe River.
The bombers flew low, at about 100 ft (30 m) altitude, to avoid radar detection. Flight Sergeant George Chalmers, radio operator on "O for Orange", looked out through the astrodome and was astonished to see that his pilot was flying towards the target along a forest's firebreak, below treetop level.
The first casualties were suffered soon after reaching the Dutch coast. Formation No. 2 did not fare well: Munro's aircraft lost its radio to flak and turned back over the IJsselmeer, while Rice flew too low and struck the sea, losing a bomb in the water; he recovered and returned to base. Both Barlow's and Byers' Lancasters crossed over the coast around the island of Texel. Byers' bomber was shot down by flak shortly afterwards, crashing into the Waddenzee. Barlow's aircraft hit electricity pylons and crashed 5km east of Rees, near Haldern. Only the delayed bomber piloted by McCarthy survived to cross the Netherlands. In addition, Formation No. 1 lost Astell's bomber near the German hamlet of Marbeck when he flew his Lancaster into high tension electrical cables and crashed into a field.[5]
Formation No. 1 arrived over the Möhne lake and Gibson's aircraft (G for George) made the first run, followed by Hopgood (M for Mother). Hopgood's aircraft was hit by flak as it made its low-level run and was caught in the blast of its own bomb, crashing shortly afterwards when a wing disintegrated. Three crew members successfully left the aircraft, but only two survived. Subsequently Gibson flew his aircraft across the dam to draw the flak away from Martin's run. Martin (P for Popsie) bombed third; his aircraft was damaged but made a successful attack. Next, Young (A for Apple) made a successful run and after him Maltby (J for Johnny) when, finally, the dam was breached. Gibson, with Young accompanying, led Shannon, Maudslay and Knight to the Eder.[5] In the attack on the Möhne one of the bombers made a running commentary on the attack, relayed to base by an airborne TR. 1142 (Transmitter Receiver) manufactured by GEC, the distance being too great for direct VHF transmission.[6]
The Eder Valley was covered by heavy fog but not defended. The tricky topography of the surrounding hills made the approach difficult and the first aircraft, Shannon's, made six runs before taking a break. Maudslay (Z for Zebra) then attempted a run but the bomb struck the top of the dam and the aircraft was severely damaged in the blast. Shannon made another run and successfully dropped his bomb. The final bomb of the formation, from Knight's aircraft (N for Nut), breached the dam.[7]
The Sorpe dam was the one least likely to be breached. It is a huge earthen dam, rather than concrete-and-steel gravity dams that were attacked successfully. Due to various problems, only three Lancasters reached the Sorpe Dam: Joe McCarthy (in "T for Tommy”, a delayed aircraft from the second wave) and later Brown ("F for Freddie") and Anderson ("Y for York"), both from the third formation. This attack differed from the previous ones in two ways: the "Upkeep" bomb was not spun, and the approach was made along the length of the dam, not at right angles over the reservoir, due to the topography of the valley.
McCarthy's plane was on its own when it arrived over the Sorpe Dam at 00:15 hours, and realised the approach was even more difficult than expected: the flight path led over a church steeple in the village of Langscheid, located on the hillcrest overlooking the dam. With only seconds to go before the bomber had to pull up, to avoid hitting the hillside at the other end of the dam, the bombardier George Johnson had no time to correct the bomb's height and heading.
McCarthy made nine attempted bombing runs before Johnson was satisfied. The 'Upkeep' bomb was dropped on the tenth run. The bomb exploded, but when he turned his Lancaster to assess the damage it turned out that only a section of the crest of the dam had been blown off: the main body of the dam itself was still functional.
Meanwhile, three of the reserve aircraft had been directed to the Sorpe Dam. Burpee ("S for Sugar") never arrived, and it was later determined that the plane had been shot down while skirting the Gilze-Rijen airfield. Brown ("F for Freddy") reached the Sorpe Dam: in the increasingly dense fog the bomb was dropped hastily and also failed to breach the dam. Anderson ("Y for York") arrived last, but by then the fog had become too dense for him even to attempt a bombing run. The remaining two bombers were then sent to secondary targets, with Ottley ("C for Charlie") being shot down en-route to the Lister Dam. Townsend ("O for Orange") eventually dropped his bomb at the Ennepe Dam without harming it.[5]
There is some evidence that Townsend might have attacked the Bever Dam by mistake rather than the Ennepe Dam.[8] Townsend reported difficulty in finding his dam, and in his post-raid report he complained that the map of the Ennepe Dam was incorrect. The Bever Dam is located only about 5 mi (8 km) southwest of the Ennepe Dam, and its reservoir has a similar topography. However, the Bever Dam is located on the southern edge of the reservoir while the Ennepe is located on the northern edge of its reservoir. With the foggy mists filling the valleys during the early morning hours, it would be understandable for him to have mistaken the two lakes. The War Diary of the German Naval Staff reported that the Bever Dam had been attacked at nearly the same time that the Sorpe Dam was. In addition, the Wupperverband authority responsible for the Bever Dam is said to have recovered the remains of a "mine". Paul Keiser, a 19-year-old soldier on leave at his home close to the Bever Dam, also reported a bomber making several approaches to the dam and then dropping a bomb that caused a large explosion and a great pillar of flame.
John Sweetman, author of the book The Dambusters' Raid, suggests Townsend's report of the moon's reflecting on the mist and water is consistent with an attack that was heading to the Bever Dam rather than to the Ennepe Dam, given the moon's azimuth and altitude during the bombing attacks. Sweetman also points out that the Ennepe-Wasserverband authority was adamant that only a single bomb was dropped near the Ennepe Dam during the entire war, and that this bomb fell into the woods by the side of the dam, not in the water, as in Townsend's report. Finally, members of Townsend's crew independently reported seeing a manor house and attacking an earthen dam, which is consistent with the Bever Dam rather than the Ennepe Dam. The main evidence supporting the hypothesis of an attack of the Ennepe Dam is Townsend's post-flight report that he attacked the Ennepe Dam on a heading of 355 degrees magnetic. Assuming that the heading was incorrect, all other evidence points toward an attack on the Bever Dam.[8]
On the way back, flying again at treetop level, two more Lancasters were lost. The damaged "Z for Zebra" was struck by flak near Netterden and Young's "A for Apple" was flayed by flak north of IJmuiden. That bomber crashed into the North Sea just off the coast of the Netherlands.[5] However, on the return flight over the Dutch coast, some German flak targeting the planes was aimed so low that shells were seen to bounce off the sea.[9]
The nine surviving bombers began landing at Scampton at 03:11 hours, with Gibson returning at 04:15 hours. The last of the survivors, Townsend's bomber, put its wheels on the ground at 06:15 hours.[5] Flying downwind and into the sun they had a rather bumpy landing as one of their engines had been badly damaged.
| Aircraft call sign | Commander | Target | Returned? | Notes |
|---|---|---|---|---|
| First Wave | ||||
| G George | Gibson | Möhne Dam | Yes | Raid leader. Mine exploded short of dam. Used aircraft to draw anti-aircraft fire away from other crews. |
| M Mother | Hopgood | No | Hit by anti-aircraft fire outbound. Mine bounced over dam. Shot down over the target while attacking. | |
| P Peter (Popsie) | Martin | Yes | Mine missed the target. | |
| A Apple | Young | No | Mine hit dam and caused small breach. Shot down over the Dutch coast while returning. | |
| J Johnny | Maltby | Yes | Mine hit dam and caused a large breach. | |
| L Leather | Shannon | Eder Dam | Yes | Mine hit target—no effect. |
| Z Zebra | Maudslay | No | Mine overshot target and damaged the bomber, which was shot down over Germany while trying to return. | |
| N Nancy (Nan) | Knight | Yes | Mine hit the dam and caused a large breach. | |
| B Baker | Astell | N/A | No | Crashed after hitting large-scale power lines outbound. |
| Second Wave | ||||
| T Tommy | McCarthy | Sorpe Dam | Yes | Mine hit the target – no apparent effects. |
| E Easy | Barlow | N/A | No | Crashed after hitting large-scale power lines outbound. |
| K King | Byers | No | Shot down over the Dutch coast outbound. | |
| H Harry | Rice | Yes | Lost the mine after clipping the ocean outbound. Returned without attacking a target. | |
| W Willie | Munro | Yes | Damaged by anti-aircraft fire over the Dutch coast. Returned without attacking a target. | |
| Third Wave | ||||
| Y York | Anderson | Sorpe Dam | Yes | Could not find the target due to the mist. Landed at Scampton with an armed mine. |
| F Freddy | Brown | Sorpe Dam | Yes | Mine hit the target – no apparent effects. |
| O Orange | Townsend | Ennepe Dam | Yes | Mine hit the target – no apparent effect. |
| S Sugar | Burpee | N/A | No | Shot down over the Netherlands outbound. |
| C Charlie | Ottley | No | Shot down over Germany outbound. | |
Bomber Command wanted a complete bomb damage assessment as soon as possible, therefore the CO of 542 Squadron was informed of the estimated time of the attacks. One of the squadron's photo-reconnaissance Spitfires, piloted by Flying Officer Frank "Jerry" Fray,[10] took off from RAF Benson at 07:30 hours and arrived over the Ruhr River immediately after first light. Photos were taken of the breached dams and the huge floods.[11] The pilot later described the experience:[10]
| “ | When I was about 150 miles from the Möhne Dam, I could see the industrial haze over the Ruhr area and what appeared to be a cloud to the east. On flying closer, I saw that what had seemed to be cloud was the sun shining on the floodwaters.
I looked down into the deep valley which had seemed so peaceful three days before [on an earlier reconnaissance mission] but now it was a wide torrent. The whole valley of the river was inundated with only patches of high ground and the tops of trees and church steeples showing above the flood. I was overcome by the immensity of it. |
” |
Three aircrew from Hopgood's aircraft bailed out successfully, but one later died from wounds while the others were captured. One of the crew in Ottley's aircraft survived its crash. In total, therefore, 53 of the 133 aircrew who participated in the attack were killed, a casualty rate of almost 40%. Thirteen of those killed were members of the Royal Canadian Air Force, while two belonged to the Royal Australian Air Force.[12]
Of the survivors, 34 were decorated at Buckingham Palace on 22 June, with Gibson awarded the Victoria Cross. There were five Distinguished Service Orders, 10 Distinguished Flying Crosses and four bars, two Conspicuous Gallantry Medals, and eleven Distinguished Flying Medals and one bar.[13]
Initial German casualty estimates from the floods when the dams broke were about 1,294 killed, which included 749 French, Belgian, Dutch and Ukrainian prisoners of war and labourers.[14][15]
After a public relations tour of America and time spent working in the Air Ministry in London writing the book which would later be published as Enemy Coast Ahead, Gibson returned to operations and was killed on a Mosquito operation in 1944.
Following the Dams Raid 617 Squadron was kept together as a specialist unit. The squadron badge was chosen and a motto "Après moi le déluge" (After me the flood). According to Brickhill there was some controversy over the motto, with the original version Après nous le déluge (After us the flood) being rejected by the heralds as having inappropriate provenance (having been coined, reportedly, by Madame de Pompadour), and après moi le déluge having been used by Louis XV in an "irresponsible" context. The motto having been chosen by the King, the latter was finally deemed acceptable.[16]
The squadron went on to drop Wallis' massive Tallboy and Grand Slam bombs, including an attack on the German battleship Tirpitz, using an advanced bomb sight which enabled the bombing of small targets with far greater accuracy than was routinely obtained with conventional bomb aiming techniques. The squadron is still active today.
In 1977, Article 56 of the Protocol I amendment to the Geneva Conventions, outlawed attacks on dams "if such attack may cause the release of dangerous forces from the works or installations and consequent severe losses among the civilian population".[17]
The two direct mine hits on the Möhnesee dam resulted in a breach around 250 feet (76 meters) wide and 292 feet (89 meters) deep. The destroyed dam poured around 330 million tons of water (equivalent to a cube 687 meters on each side) into the western Ruhr region. A torrent of water around 32.5 feet (10 meters) high and travelling at around 15 mph (24 km/h) swept through the valleys of the Möhne and Ruhr rivers. A few underground mines were flooded; 11 small factories and 92 houses were destroyed and 114 factories and 971 houses were damaged. The floods washed away about 25 roads, railways and bridges as the flood waters spread for around 50 miles (80 km) from the source. Estimates show that before 15 May 1943 water production on the Ruhr was 1 million tonnes, this dropped to a quarter of that level after the raid.
The Eder drains towards the east into the Fulda which runs into the Weser to the North Sea. The main purpose of the Edersee is (even today) to act as a reservoir to keep the Weser and the Mittellandkanal shippable during the summer months. The wave from the breach wasn't strong enough to result in considerable damage when it hit Kassel (approx. 35 km downstream).
The loss of hydro-electric power for the dams was the greatest impact on the Ruhr armaments production. Two powerplants (producing 5,100 kilowatts) associated with the dam were destroyed and seven others were damaged. The end result was a loss of electrical power in the factories and many households in the region for two weeks.
In terms of deaths: according to the latest sources,[18] at least 1,650 people were killed: around 70 in the Eder Valley, and at least 1,579 bodies were found along the Möhne and Ruhr rivers, with hundreds missing. 1,026 of the bodies found downriver of the Möhne Dam were foreign prisoners of war and forced-labourers in different camps, mainly from the Soviet Union. Worst hit was the city of Neheim (now part of Neheim-Hüsten) at the confluence of the Möhne and Ruhr rivers, where over 800 people perished, among them at least 493 female forced-labourers from the Soviet Union. (Some non-German sources erroneously cite an earlier total of 749 for all foreigners in all camps in the Möhne and Ruhr valleys as the casualty count at a camp just below the Eder Dam.[15])
After the operation Barnes Wallis wrote, "I feel a blow has been struck at Germany from which she cannot recover for several years." However, on closer inspection, Operation Chastise did not have the military effect that was at the time believed. By 27 June, full water output was restored, thanks to an emergency pumping scheme inaugurated only the previous year, and the electricity grid was again producing power at full capacity. The raid proved to be costly in lives (more than half the lives lost belonging to Allied POWs and forced-labourers), but in fact no more than a minor inconvenience to the Ruhr's industrial output.[19] The value of the bombing can perhaps best be seen as a very real boost to British morale.
In his book Inside the Third Reich, Albert Speer expressed puzzlement at the raids. While he considered the attempt as laudatory: "That night, employing just a few bombers, the British came close to a success which would have been greater than anything they had achieved hitherto with a commitment of thousands of bombers."[20] But, on the other hand, the disruption of temporarily having to shift 7,000 construction workers to the Möhne and Eder repairs was offset by the failure of the Allies to follow up with additional (conventional) raids during the dams' reconstruction, and that represented a major lost opportunity.[21] Ironically Barnes Wallis was also of this view, he revealed his deep frustration that Bomber Command never sent a high level bombing force to hit the Mohne dam whilst repairs were being carried out. He argued that extreme precision would have been unnecessary and that even a few hits by conventional HE bombs would have prevented the rapid repair of the dam which was undertaken by the Germans ("Bomber Command" p262 Max Hastings)
The effect on food production was more significant with many square kilometers of arable land being washed away and effectively unusable until the 1950s. There was also a great loss of farm animals bred for food.
The Dams Raid was, like many British air raids, undertaken with a view to the need to keep drawing German defensive effort back into Germany and away from actual and potential theatres of ground war, a policy which culminated in the Berlin raids of the winter of 1943–1944. In May 1943 this meant keeping the Luftwaffe and anti-aircraft defence forces' effort away from the Soviet Union; in early 1944, it meant clearing the way for the aerial side of the forthcoming Operation Overlord.
The pictures of the broken dams proved to be a propaganda and morale boost to the Allies, especially to the British, still suffering under German bombing.[10]
An associated, but equally major effect was that Barnes Wallis's ideas on earth quake bombing, which had been rejected before, now became accepted by 'Bomber' Harris. Prior to this raid, bombing practice had been to 'area bomb' with many light bombs, in the hope that one would hit the target. Work on the earthquake bomb theory resulted in the Tallboy and Grand Slam weapons, which caused unprecedented damage to German infrastructure in the later stages of the war. They rendered the V-2 assembly building unusable, buried the V-3 guns, sank the Tirpitz and destroyed many bridges and other hardened installations. Notable amongst their successes were the U-Boat pens at Brest, where they penetrated 20 ft (6.1 m) thick roofs of reinforced concrete, and the Saumur Tunnel.
An important reason for planning the raid was to persuade Joseph Stalin that Britain was capable of being an effective ally. Stalin often called upon the Western Allies to open a second front: the Dambusters raid provided the British with a valuable opportunity to prove that they were harrying the Germans in every way they could while building up forces for an eventual liberation of Western Europe. However, by the time the preparations for the British raid were complete, the USSR had managed to fight back against German forces; the USSR had also found the capacity to begin its counter-offensive on the Don and Volga. The Dams Raid enabled Churchill, in negotiations with the leaders of these new allies, to point to new, effective strikes after 1942's "1,000-bomber raids" against cities and shortly before the devastating late-July 1943 bombing of Hamburg. As a result, he was taken more seriously as an ally than might otherwise have been the case. This was most relevant in negotiations with Stalin, but also to a lesser degree in the USA. Although Churchill had the sympathetic ear of Roosevelt, many of the US military staff had until then been less persuaded of the value of British experience and capabilities.[22]
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