Operation Chastise

Air Vice-Marshal Ralph Cochrane, Wing Commander Guy Gibson, King George VI and Group Captain John Whitworth discussing the Dambuster Raid in May 1943

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 more than 170 bombing and night-fighter missions, twenty-one bomber crews were selected from 5 Group squadrons. The crews included RAF personnel of several nationalities, members of the Royal Australian Air Force (RAAF), Royal Canadian Air Force (RCAF) and Royal New Zealand Air Force (RNZAF). The squadron was based at RAF Scampton, about 5 mi (8 km) north of Lincoln.

The targets selected were the Möhne Dam and the Sorpe Dam, upstream from the Ruhr industrial area, with the Eder Dam on the Eder River, which feeds into the Weser, as a secondary target. The loss of hydroelectric power was important but the loss of water to industry, cities and canals would have greater effect and there was potential for devastating flooding if the dams broke.

"Upkeep" bouncing bomb mounted under Gibson's Lancaster B III (Special)

Barnes Wallis and others watch a practice Upkeep bomb strike the shoreline at Reculver, Kent.

Bombing from an altitude of 60 ft (18 m), at an air speed of 240 mph (390 km/h) and at set 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, owing to problems 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, near Uppingham, Rutland; Abberton Reservoir near Colchester; Derwent Reservoir in Derbyshire; and Fleet Lagoon on Chesil Beach. Wallis's bomb itself was first tested at the Elan Valley Reservoirs.

The squadron took delivery of the bombs 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, Flt 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 formations.

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 Pilot 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), P/O Vernon Byers (RCAF), Flt Lt Norman Barlow (RAAF), P/O Geoff Rice[14] 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 to attack three smaller secondary target dams: the Lister, the Ennepe and the Diemel.

Two crews were unable to make the mission owing 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.[15] Dinghy was Young's nickname, a reference to the fact that he had twice survived crash landings at sea where he and his crew were rescued from the aircraft's inflatable rubber dinghy.

The aircraft used two routes, carefully avoiding known concentrations of 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 on 16 May.[16] McCarthy's bomber developed a coolant leak and he took off in the reserve aircraft 34 minutes late.[17]

Formation No. 1 took off in groups of three at 10-minute intervals beginning at 21:39.[16] The reserve formation did not begin taking off until 00:09 on 17 May.[16]

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.[18]

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.[19]

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[14] flew too low and struck the sea, losing his bomb in the water; he recovered and returned to base. After the completion of the raid Gibson sympathised with Rice, telling him how he had also nearly lost his bomb to the sea.

Barlow and Byers crossed the coast around the island of Texel. Byers was shot down by flak shortly afterwards, crashing into the Waddenzee. Barlow's aircraft hit electricity pylons and crashed 5 km east of Rees, near Haldern. The bomb was thrown clear of the crash and was examined intact by Heinz Schweizer.[20] Only the delayed bomber piloted by McCarthy survived to cross the Netherlands. Formation No. 1 lost Astell's bomber near the German hamlet of Marbeck when his Lancaster hit high voltage electrical cables and crashed into a field.[16]

Möhne Dam after the attack

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 abandoned 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.[16] 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.[21]

Eder Dam on 17 May 1943

Eder Dam in 2004: the destroyed sluice-gate channels on the left were not replaced after the attack.

The Eder Valley was covered by heavy fog, but the dam was not defended with anti-aircraft positions as the difficult topography of the surrounding hills was thought to make an attack virtually impossible. With approach so difficult 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.[22]

The Sorpe dam was the one least likely to be breached. It was a huge earthen dam, unlike the two concrete-and-steel gravity dams that were attacked successfully. Due to various problems, only two Lancasters reached the Sorpe Dam: Joe McCarthy (in T for Tommy, a delayed aircraft from the second wave) and later Brown (F for Freddie) from the third formation. This attack differed from the previous ones in two ways: the 'Upkeep' bomb was not spun, and due to the topography of the valley the approach was made along the length of the dam, not at right angles over the reservoir.

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 bomb aimer George Johnson had no time to correct the bomb's height and heading.

The crew of "T for Tommy"

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 remained.

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 Freddie) reached the Sorpe Dam: in the increasingly dense fog, after 7 runs, Brown conferred with his bomb aimer and dropped incendiary devices on either side of the valley, which ignited a fire which subsequently lifted the fog enough to drop a direct hit on the eighth run. The bomb cracked but failed to breach the dam. Anderson (Y for York) never arrived having been delayed by damage to his rear turret and dense fog which made his attempts to find the target impossible. 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.[16]

There is some evidence that Townsend might have attacked the Bever Dam by mistake rather than the Ennepe Dam.[23] The War Diary of the German Naval Staff reported that the Bever Dam was 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"; and Paul Keiser, a 19-year-old soldier on leave at his home close to the Bever Dam, 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.

In the book The Dambusters' Raid, author John Sweetman 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.[23]

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 only about 5 mi (8 km) southwest of the Ennepe Dam. With the early-morning fog that filled the valleys, it would be understandable for him to have mistaken the two reservoirs.

On the way back, flying again at treetop level, two more Lancasters were lost. The damaged aircraft of Maudslay was struck by flak near Netterden, and Young's (A for Apple) was hit by flak north of IJmuiden and crashed into the North Sea just off the coast of the Netherlands.[16] On the return flight over the Dutch coast, some German flak aimed at the aircraft was aimed so low that shells were seen to bounce off the sea.[24]

Eleven bombers began landing at Scampton at 03:11 hours, with Gibson returning at 04:15. The last of the survivors, Townsend's bomber, landed at 06:15.[16] It was the last to land because one of its engines had been shut down after passing the Dutch coast. Air Chief Marshal Harris was among those who came out to greet the last crew to land.[25]

The two direct mine hits on the Möhnesee dam resulted in a breach around 250 feet (76 m) wide and 292 feet (89 m) deep. The destroyed dam poured around 330 million tons of water into the western Ruhr region. A torrent of water around 33 feet (10 m) high and travelling at around 15 miles per hour (24 km/h) swept through the valleys of the Möhne and Ruhr rivers. A few 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 steel 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 was then, as it is now, to act as a reservoir to keep the Weser and the Mittellandkanal navigable during the summer months. The wave from the breach was not strong enough to result in significant damage by the time it hit Kassel, approximately 22 miles (35 km) downstream.

The greatest impact on the Ruhr armaments production was the loss of hydroelectric power. Two power stations (producing 5,100 kilowatts) associated with the dam were destroyed and seven others were damaged. This resulted in a loss of electrical power in the factories and many households in the region for two weeks. In May 1943 coal production dropped by 400,000 tons which German sources attribute to the effects of the raid.[34]

According to an article by German historian Ralf Blank,[35] at least 1,650 people were killed: around 70 of these were 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.[31]) One source states that the raid was no more than a minor inconvenience to the Ruhr's industrial output, although that is in direct contradiction to the previous paragraphs with multiple citations.[36] The bombing boosted British morale.[37]

In his book Inside the Third Reich, Albert Speer acknowledged the attempt: "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."[38] He also expressed puzzlement at the raids: 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.[39] 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 while 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.[40]

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 aircraft and anti-aircraft defences away from the Soviet Union; in early 1944, it meant clearing the way for the aerial side of the forthcoming Operation Overlord. The considerable amount of labour and strategic resources committed to repairing the dams, factories, mines and railways could not be used in other ways, on the construction of the Atlantic Wall, for example. The pictures of the broken dams proved to be a propaganda and morale boost to the Allies, especially to the British, still suffering from the German bombing of the Baedeker Blitz that had peaked roughly a year earlier.[26]

Even within Germany, as evidenced by Gauleiters' reports to Berlin at the time, the German population regarded the raids as a legitimate attack on military targets and thought they were "an extraordinary success on the part of the English" [sic]. They were not regarded as a pure terror attack by the Germans, even in the Ruhr region, and in response the German authorities released relatively accurate (not exaggerated) estimates of the dead.[41]

An effect of the dam raids was that Barnes Wallis's ideas on earthquake bombing, which had previously been rejected, came to be accepted by 'Bomber' Harris. Prior to this raid, bombing had used the tactic of area bombardment with many light bombs, in the hope that one would hit the target. Work on the earthquake bombs resulted in the Tallboy and Grand Slam weapons, which caused damage to German infrastructure in the later stages of the war. They rendered the V-2 rocket launch complex at Calais unusable, buried the V-3 guns, and destroyed bridges and other fortified installations, such as the Grand Slam attack on the railway viaduct at Bielefeld. Most notable successes were the partial collapse of 20-foot-thick (6 m) reinforced concrete roofs of U-boat pens at Brest, and the sinking of the battleship Tirpitz.

Harris regarded the raid as a failure and a waste of resources.[42]