Operation Chastise, commonly known as the Dambusters Raid, was an attack on German dams carried out on the night of 16/17 May 1943 by 617 Squadron RAF Bomber Command, later called the Dam Busters, using special bouncing bombs 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; the Sorpe Dam sustained only minor damage. Two hydroelectric power stations were destroyed and several more damaged. Factories and mines were also damaged and destroyed. An estimated 1,600 civilians – about 600 Germans and 1,000 enslaved labourers, mainly Soviet – were killed by the flooding. Despite rapid repairs by the Germans, production did not return to normal until September. The RAF lost 56 aircrew, with 53 dead and three captured, amid losses of eight aircraft.
Background
Before the Second World War, the British Air Ministry had identified the industrialised Ruhr Valley, especially its dams, as important strategic targets. The dams provided hydroelectric power and pure water for steel-making, drinking water and water for the canal transport system. Calculations indicated that attacks with large bombs could be effective but required a degree of accuracy which RAF Bomber Command had been unable to attain when attacking a well-defended target. A one-off surprise attack might succeed but the RAF lacked a weapon suitable for the task.
Concept
thumb|upright|left|1:50 scale model of the Möhne Dam, Building Research Establishment
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 bomb from an altitude of about , part of the earthquake bomb concept. No bomber aircraft was capable of flying at such an altitude or of carrying such a heavy bomb and although Wallis proposed the six-engined Victory Bomber for this purpose this was rejected. Wallis realised that 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 an explosive device from travelling through the water.
Wallis devised a bomb (more accurately, a mine) in the shape of a cylinder, equivalent to a very large depth charge armed with a hydrostatic fuse, designed to be given a backspin of 500 rpm. Dropped at and from the release point, the mine would skip across the surface of the water before hitting the dam wall as its forward speed ceased. Initially the backspin was intended to increase the range of the mine but it was later realised that it would also cause the mine, after submerging, to run down the side of the dam towards its base, thus maximising the explosive effect against the dam. This weapon was code-named Upkeep.
thumb|upright|Remains of the [[Elan Valley Reservoirs|Nant-y-Gro dam breached in July 1942 during testing]]
Testing of the concept included blowing up a scale 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. A subsequent test suggested that a charge of exploded under water would breach a full-size dam; crucially this weight would be within the carrying capacity of an Avro Lancaster. The first air drop trials were at Chesil Beach in December 1942; these used a spinning sphere dropped from a modified Vickers Wellington, serial BJ895/G; the same aircraft was used until April 1943 when the first modified Lancasters became available. The tests continued at Chesil Beach and Reculver, often unsuccessfully, using revised designs of the mine and variations of speed and height.
Avro Chief Designer Roy Chadwick adapted the Lancaster to carry the mine. To reduce weight, much of the internal armour was removed, as was the mid-upper (dorsal) gun turret. The dimensions of the mine and its unusual shape meant that the bomb-bay doors had to be removed and the mine hung partly below the fuselage. It was mounted on two crutches and before dropping it was spun by an auxiliary motor. Chadwick also worked out the design and installation of controls and gear for the carriage and release of the mine in conjunction with Barnes Wallis. The Avro Lancaster B Mk IIIs so modified were known as Lancaster B Mark III Special (Type 464 Provisioning).
thumb|Using two spotlights to ascertain the required height, a modified [[Avro Lancaster|Lancaster dropped a backspun drum-bomb which skipped over the torpedo nets protecting the dam. After impact, the bomb spun down to the dam's base and exploded.]]
In February 1943, Air Vice-Marshal Francis Linnell at the Ministry of Aircraft Production thought the work was diverting Wallis from the development of the Vickers Windsor bomber (which did not become operational). Pressure from Linnell via the chairman of Vickers, Sir Charles Worthington Craven, caused Wallis to offer to resign. Sir Arthur Harris, head of Bomber Command, after a briefing by Linnell also opposed the allocation of his bombers; Harris was about to start the strategic bombing campaign against Germany and Lancasters were just entering service. 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 over-ruled 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 mine that was needed for the mission and the modifications to the Lancasters had yet to be designed.
Assignment
thumb|left|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, later to be named No. 617 Squadron, 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, 21 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 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.
Preparations
thumb|Barnes Wallis and others watch a practice Upkeep bomb strike the shoreline at [[Reculver, Kent.]]
Bombing from an altitude of , at an air speed of and at set distance from the target called for expert crews. Intensive night-time and low-altitude 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. 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 ultimately 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 barometric altimeters lacked 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 the Derbyshire Peak District; and Fleet Lagoon on Chesil Beach. Wallis's bomb was first tested at the Elan Valley Reservoirs.
The lights were developed by Edward Spence Calvert (1902–91), of Northern Ireland, at the RAE in Hampshire, with an initial proposal by Ben Lockspeiser. After the war, Calvert, with his assistant Jack Sparke, developed the system of aircraft landing lights mostly found across British airports today, known as 'centre line and crossbar' approach lighting system, first tested in the Berlin Airlift. The ICAO adopted the Calvert approach system in 1952. All NATO airfields have the lighting system, with six transverse rows of lights. With Jack Sparke, he also developed the visual approach slope indicator in the late 1950s. He was head of the illumination section of the RAE from 1941 to 1967.
Gibson also had VHF radios (normally reserved for fighters) fitted to the Lancasters so that he could control the operation while over the target, an early example of what became the master bomber role.
The squadron took delivery of the bombs on 13 May, after the final tests on 29 April. At 18:00 on 15 May, at a meeting in Whitworth's house, Gibson and Wallis briefed the squadron's two flight commanders, Squadron Leader Henry Eric 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.
Organisation
thumb|left|"Upkeep" bouncing bomb mounted under Gibson's Lancaster B III (Special)
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.
History of 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 bombers flew low, at about 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.
First casualties
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; 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.
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 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 bomber'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 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 seven 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. 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.
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.
{| class="wikitable"
! Serial No !! Aircraft call sign !! Commander !! Target !! Attacked target? !! Hit target? !! Breached target? !! Returned? !! Notes
|-
! colspan="9" align="left" | First Wave
|-
| ED932 || G George || Gibson || rowspan="5" | Möhne Dam || || || || || Raid leader. Mine exploded short of dam. Used aircraft to draw anti-aircraft fire away from other crews.
|-
| ED925 || M Mother || Hopgood || || || || || Hit by anti-aircraft fire outbound. Mine bounced over dam. Shot down over the target while attacking. (P/O Fraser and P/O Burcher survived)
|-
| ED909 || P Peter (Popsie) || Martin || || || || || Mine missed the target.
|-
| ED887 || A Apple || Young || || || || || Mine hit dam and caused small breach. On the homeward flight Lancaster AJ-A was hit by anti-aircraft fire and crashed along the shoreline 2 km south of the Dutch coastal resort of Castricum aan Zee. All seven crew members lost their lives and are buried at the Bergen General Cemetery.
|-
| ED906 || J Johnny || Maltby || || || || || Mine hit dam and caused a large breach.
|-
| ED929 || L Leather || Shannon || rowspan="3" | Eder Dam || || || || || Mine hit target—no effect.
|-
| ED937 || Z Zebra || Maudslay || || || || || Mine overshot target and damaged the bomber, which was shot down over Germany while trying to return.
|-
| ED912 || N Nancy (Nan) || Knight || || || || || Mine hit the dam and caused a large breach.
|-
| ED864 || B Baker || Astell || N/A || || || || || Crashed after hitting large-scale power lines outbound.
|-
! colspan="9" align="left" | Second Wave
|-
| ED825 || T Tommy || McCarthy || Sorpe Dam || || || || || Mine hit the target – no apparent effect.
|-
| ED927 || E Easy || Barlow || rowspan="4" | N/A || || || || || Crashed after hitting power lines outbound.
|-
| ED934 || K King || Byers || || || || || Shot down over the Dutch coast outbound.
|-
| ED936 || H Harry || Rice || || || || || Lost the mine after clipping the sea outbound. Returned without attacking a target.
|-
| ED921 || W Willie || Munro || || || || || Damaged by anti-aircraft fire over the Dutch coast. Returned without attacking a target.
|-
! colspan="9" align="left" | Third Wave
|-
| ED924 || Y York || Anderson || Sorpe Dam || || || || || Could not find the target due to mist. Landed at Scampton with an armed mine.
|-
| ED918 || F Freddy || Brown || Sorpe Dam || || || || || Mine hit the target – no apparent effect.
|-
| ED886 || O Orange || Townsend || Ennepe or Bever Dam || || || || || Mine hit the target – no apparent effect.
|-
| ED865 || S Sugar || Burpee || rowspan="2" | N/A || || || || || Shot down over the Netherlands outbound.
|-
| ED910 || C Charlie || Ottley || || || || || Shot down over Germany outbound. Frederick Tees was the sole survivor
|-
| Totals || 19 aircraft || || 4 dams || 11 of 19 || 7 of 11 || 3 of 7 || 11 of 19 || 2 hit power lines outbound; 3 shot down outbound; 3 returned without attacking;
11 attacked; 1 shot down over target; 2 shot down homebound; 8 attacked target and returned.
|-
|}
Bomb damage assessment
Bomber Command wanted a bomb damage assessment as soon as possible and the CO of 542 Squadron was informed of the estimated time of the attacks. A photo-reconnaissance Spitfire, piloted by Flying Officer Frank 'Jerry' Fray, took off from RAF Benson at 07:30 hours and arrived over the Ruhr River some hours after first light. Photos were taken of the breached dams and the huge floods. The pilot later described the experience: