The mission grew out of a concept for a bomb designed by Barnes Wallis, assistant chief designer at Vickers. Wallis had worked on the Vickers Wellesley and Vickers Wellington bombers and while working on the Vickers Windsor, he had also begun work, with Admiralty support, on an anti-shipping bomb, although dam destruction was soon considered.
At first, Wallis wanted to drop a 10 long ton (22,000 lb, 10.2 tonne) bomb from an altitude of about 40,000 ft (12,200 m), part of the earthquake bomb concept. No bomber aircraft was capable of flying at such an altitude or of carrying such a heavy bomb. A much smaller explosive charge would suffice, if it exploded against the dam wall under the water but German reservoir dams were protected by heavy torpedo nets to prevent delivery of an explosive warhead through water.
Wallis then devised a 9000 pound bomb in the shape of a cylinder, equivalent to a very large depth charge armed with a hydrostatic fuse, but designed to be given backward spin of 500 rpm. Dropped at 60 ft and 240 mph from the release point, the bomb would skip across the surface of the water before hitting the dam wall. The residual backspin would submerge the bomb, running it down the side of the dam toward its base.
The first trials were at Chesil Beach in January 1943, which 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 come into service. Air Vice-Marshal 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, after a briefing by Linnell also opposed the allocation of his bombers. Wallis had written to an influential intelligence officer, Group Captain Frederick Winterbotham, who ensured that the Chief of the Air Staff, Air Chief Marshal Charles Portal, heard of the project. Portal saw the film of the Chesil Beach trials and was convinced. On 26 February 1943, Portal overruled Harris and ordered that thirty 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 Upkeep bomb that was needed for the mission and the modifications to the Lancasters had yet to be designed.
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.
The aircraft were modified Avro Lancaster Mk IIIs, known as B Mark III Special (Type 464 Provisioning). To reduce weight, much of the internal armour was removed, as was the mid-upper turret. The dimensions of the bomb and its unusual shape meant that the bomb-bay doors had to be removed and the bomb hung partly below the fuselage. It was mounted on two crutches and before dropping it was spun up to speed by an auxiliary motor.
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; 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 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. “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 attacks- Outbound
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. McCarthy’s bomber developed a coolant leak and he took off in the reserve aircraft 34 minutes late.
Formation No. 1 took off in groups of three at 10-minute intervals beginning at 21:39. The reserve formation did not begin taking off until 00:09 on 17 May.
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 his bomb in the water; he recovered and returned to base. 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. 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.
Attack on the Möhne Dam
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. 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.
Attack on the Eder Dam
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.
Attacks on the Sorpe and Ennepe Dams
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 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 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 conferenced 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.
Possible attack on Bever Dam
There is some evidence that Townsend might have attacked the Bever Dam by mistake rather than the Ennepe Dam. 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.
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, and both are similarly on the edges of their reservoirs. 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. 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.
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. 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.