Operation Chastise

On the night of 16–17 May 1943 nineteen Avro Lancaster bombers of the specially formed No. 617 Squadron of RAF Bomber Command attacked dams in western Germany from a height of some twenty metres. Armed with spinning “bouncing bombs” designed by the engineer Barnes Wallis, the crews led by Wing Commander Guy Gibson breached the Möhne dam, which held back a reservoir feeding the Ruhr river, and the dam of the Edersee lake on the river Eder. The third of the main dams, the Sorpe, was damaged but held. The flood wave devastated the Möhne and Ruhr valleys, killing about 1,600 people, most of them forced labourers and prisoners of war from occupied Europe. The British lost eight of the nineteen aircraft and 53 airmen.

Operation Chastise, known in Britain as the Dambusters Raid, has gone down in legend as the most daring air raid of the war. The often-repeated claim that the armaments industry of the Ruhr lost its electricity supply as a result needs qualifying, however: most of the interruptions to power and water supplies lasted a few weeks, and production quickly returned to normal.

Background: dams as a target

Even before the war the British Air Ministry had identified the dams around the Ruhr industrial region as strategic targets. The reservoirs supplied water to steelworks, mines and towns, regulated the level of rivers and navigable canals, and their hydroelectric stations supported the region’s power grid. The Möhne reservoir, holding about 130 million cubic metres of water, was the main reservoir for the Ruhr; the Edersee, larger still, kept the Weser and the Mittelland Canal navigable. The problem was that the massive walls of stone and concrete required a degree of accuracy that night bombers could not achieve, and the dams were protected by anti-torpedo nets.

Barnes Wallis, assistant chief designer at Vickers, had been looking for a solution since the early years of the war. He concluded that a gigantic bomb was not needed if the charge exploded underwater right against the wall. He designed a cylindrical mine, code-named Upkeep, known in English as the bouncing bomb. It weighed about 4.2 tonnes, of which about 3 tonnes was Torpex explosive. Before release a motor gave it a backspin of about 500 revolutions per minute. Dropped from a height of 60 feet (18 metres) at about 390 km/h, it skipped across the water like a stone in a game of ducks and drakes, jumped the nets and struck the wall; then, thanks to its spin, it sank down the face of the dam to a depth of about 9 metres, where a hydrostatic fuse detonated it. The water pressure directed the force of the explosion into the structure of the dam.

Trials with models and with the disused Nant-y-Gro dam in Wales in 1942 confirmed the theory, but the project had its opponents. The commander of Bomber Command, Air Chief Marshal Arthur Harris, who was just launching the Battle of the Ruhr, regarded it as a fantasy that would divert the best aircraft from the main offensive. The fate of the operation was decided by the Chief of the Air Staff, Charles Portal: after watching film of the trials on 26 February 1943 he ordered thirty Lancasters to be modified. Fewer than eight weeks remained before the attack, and the final version of the bomb still did not exist. The date was set for mid-May, when the reservoirs are at their fullest and a full moon makes low flying at night possible.

Squadron X

The task was given to No. 5 Group of Bomber Command, which in March 1943 formed a new squadron at RAF Scampton near Lincoln, at first called simply “Squadron X” and soon No. 617 Squadron. Command went to the 24-year-old Guy Gibson, a veteran of more than 170 operational sorties in bombers and night fighters. The crews were selected from experienced airmen of No. 5 Group; alongside the British they included members of the Royal Canadian Air Force, the Royal Australian Air Force and the Royal New Zealand Air Force, as well as an American in Canadian uniform, Joe McCarthy. For six weeks they practised flying at night at a height of a few dozen feet over British reservoirs. During the same period the rest of Bomber Command was bombing the cities of the Ruhr and, in April, even reaching out to distant targets such as Stuttgart and Pilsen.

Two technical problems had to be solved. The height of exactly 60 feet above the water was set by two spotlights under the fuselage, angled so that their pools of light merged into one on the surface. The bomb aimer judged the distance from the wall with a simple wooden sight, in which two pegs lined up with the towers on the crest of the dam. Gibson also had VHF radio telephones fitted to the aircraft so that he could direct the attack from above the target – the germ of the later role of the “master of ceremonies” (master bomber). The modified Lancasters were stripped of some armour, the dorsal turret and the bomb-bay doors; the bomb was slung partly below the fuselage. The squadron received the finished bombs only on 13 May, and most crews learned their targets at briefings on 16 May, a few hours before take-off.

The raid on the night of 16–17 May

On the evening of 16 May, at about half past nine British time, three formations took off from Scampton. The first, nine aircraft led by Gibson, was to attack the Möhne, after which those aircraft still carrying bombs were to fly on to the Eder. The second, of five aircraft, took a longer northern route to the Sorpe. The third, five reserve aircraft, took off after midnight to make good losses or strike at smaller dams. The bombers flew over the Netherlands at a height of a few dozen metres, below radar cover, and suffered losses as early as the coast: one aircraft was shot down by anti-aircraft fire, two crashed into high-voltage power lines, one turned back with a damaged radio, and another, flying too low, clipped the sea and lost its bomb.

At the Möhne Gibson made the first run shortly after midnight. The second aircraft, John Hopgood’s, was hit by anti-aircraft fire and crashed beyond the dam. Gibson then flew along the wall beside each of the following attackers to draw the fire on himself. The third attack was made by the Australian Harold “Micky” Martin, the fourth by Henry “Dinghy” Young, whose bomb exploded right against the wall; after the fifth drop, by David Maltby, the wall gave way. The breach was some 75 metres wide, and within a few hours more than 100 million cubic metres of water had poured out of the reservoir. Gibson flew on to the Eder with the rest of the formation. That dam had no anti-aircraft defences, because the Germans had judged that the steep, wooded slopes of the valley ruled out an attack. The terrain was indeed so difficult that the first crew made several unsuccessful runs, and Henry Maudslay’s bomb struck the crest of the wall, the explosion damaging his aircraft. The dam was breached only by the last bomb, dropped by the Australian Les Knight.

Only two aircraft reached the Sorpe. The Sorpe was not a masonry dam but an earth dam with a concrete core, resistant to this method; here the bombs were dropped without spin, along the crest. McCarthy released his only on his tenth run, and the Canadian Ken Brown, in thickening mist, on his eighth. The explosions damaged the crest, but the dam held. The last bomb fell near the Ennepe (PL) dam without damaging it; some historians believe the crew mistakenly attacked the nearby Bever dam. On the way home anti-aircraft fire brought down two more aircraft, among them Young’s, which crashed into the sea off the Dutch coast. The last Lancaster landed at Scampton at 6.15 a.m. on 17 May; Harris was waiting for it.

Of the 133 airmen who took part in the operation, 53 were killed and three were taken prisoner – losses of almost 40 per cent. The dead included thirteen Canadians and two Australians.

The flood and its victims

The wave from the breach in the Möhne dam, initially some 10 metres high, swept down the Möhne valley and on down the Ruhr, flooding villages and towns along a stretch of several dozen kilometres; isolated deaths were recorded as far away as Essen-Steele. It destroyed or damaged more than a hundred industrial plants and over a thousand houses, swept away bridges, roads and railway lines, and flooded some of the mines. Two hydroelectric power stations at the dams were destroyed and several others damaged. The wave from the Edersee caused damage in the valleys of the Eder and the Fulda, but had lost much of its force by the time it reached Kassel.

The most tragic toll was in the town of Neheim (today part of Arnsberg), a dozen or so kilometres below the Möhne dam. In the valley there stood the Möhnewiesen camp for female forced labourers, mainly Ostarbeiter – women deported from the occupied territories of the USSR. The huts were swept away within minutes. According to the German historian Ralf Blank, more than 800 people died in Neheim alone, including at least 493 Soviet female forced labourers (other studies give more than 520). The first German tallies spoke of 1,294 dead, including 749 prisoners of war and labourers from France, Belgium, the Netherlands and Ukraine. According to Blank’s later findings, at least 1,650 people died: about 70 in the Eder valley and at least 1,579 along the Möhne and the Ruhr, with hundreds more missing. More than a thousand of the victims below the Möhne dam were foreign prisoners of war and forced labourers, mainly from the USSR. The most commonly cited figure is about 1,600 dead, of whom some 1,000 were forced labourers and prisoners of war and about 600 Germans.

The RAF planners knew that breaching the dams meant flooding inhabited valleys, but they regarded civilian casualties as a side effect of an attack on industrial infrastructure. The paradox of the raid is that its main victims turned out to be people whom the Third Reich had brought by force to work in its industry. After the war, attacks on dams that may cause severe losses among the civilian population were in principle prohibited by Additional Protocol I to the Geneva Conventions of 1977.

The effect on industry

The damage was serious but short-lived. The loss of power paralysed some factories and households in the region for about two weeks. In May coal output in the Ruhr fell by about 400,000 tons, which German sources attributed to the effects of the raid. The drinking-water supply was restored by the end of June thanks to an emergency plan prepared a year earlier, and the power grid was repaired at about the same time. The most important dam in the region, the Sorpe, had survived, and with it a large part of the water reserves.

The Armaments Minister, Albert Speer, who flew over the devastated valleys on the morning of 17 May, admitted in his post-war memoirs that that night, with just a few bombers, the British had come close to a success greater than anything they had so far achieved with thousands of aircraft. At the same time he pointed to their mistake: Bomber Command did not follow up with attacks with conventional bombs during the reconstruction, although an ordinary raid on the building sites could have halted it for a long time. Wallis shared this view. Speer moved some 7,000 workers of the Organisation Todt to the repair work, some of them taken from the construction of the Atlantic Wall, and the dams were closed before the autumn rains of 1943. Their defences were also strengthened: barrage balloons, nets, anti-aircraft guns and smoke screens.

Propaganda and decorations

Reconnaissance photographs taken from a Spitfire on the morning of 17 May showed the flooded valleys and the breach in the Möhne dam. The British press and newsreels made them a symbol of retribution for the Blitz and proof that the RAF could strike Germany with surgical precision. Winston Churchill, who was then in Washington for the Trident Conference, mentioned the attack on the dams in his speech to Congress on 19 May. The raid also mattered for relations with the allies: it showed the Americans, and Stalin, who was demanding a second front, that Britain was waging war in Germany itself. German war communiqués admitted that the dams had been damaged and stressed the losses among the civilian population, without revealing the scale of the damage.

Guy Gibson was awarded the Victoria Cross, Britain’s highest gallantry award. In all, 34 participants in the raid were decorated by King George VI at Buckingham Palace on 22 June 1943. Gibson was then sent on a propaganda tour of the United States and Canada. No. 617 Squadron was not disbanded: it remained a special-duties unit with the motto “Après moi le déluge” (“After me, the flood”).

Significance

Operation Chastise was a tactical masterpiece, but not a strategic breakthrough. The destruction of two dams did not stop the industry of the Ruhr, and the weight of the Battle of the Ruhr continued to rest on night raids by hundreds of bombers on cities, the largest of which in May fell at the end of the month on Wuppertal. The raid nevertheless proved that a small, specialised unit with a weapon designed for a single task could hit point targets that an entire armada had been unable to strike. The lessons learned from it shaped the later operations of No. 617 Squadron, which in 1944–1945 dropped Wallis’s heavy Tallboy and Grand Slam bombs on U-boat pens, viaducts and tunnels, and in November 1944 sank the battleship Tirpitz. Gibson was killed on 19 September 1944 when his Mosquito crashed near Steenbergen in the Netherlands.

The legend of the “Dambusters”, immortalised in the 1955 film, long overshadowed the other side of that night: the women from the East drowned in the huts at Neheim and the German inhabitants of the flooded valleys. In the history of air warfare the raid has remained an example both of courage and ingenuity and of how difficult it was to decide the outcome of the war by bombing industry.