A drawing of aircraft's in flight and an explosion on a dam.
Historic photography Second World War

The Story of the Dambusters: Operation Chastise, May 1943

From bouncing marbles across a garden water butt to the development of a deadly bouncing bomb, discover the extraordinary story of the Dambusters’ raid.

Operation Chastise, known as the Dambusters’ Raid, was an attack by the Royal Air Force on German dams in May 1943, using revolutionary ‘bouncing bombs’.

What was the Dambusters Raid?

On the night of 16 and 17 May 1943, in one of the most daring operations of the Second World War, the RAF’s specially formed 617 Squadron attacked three main dams in Germany’s Ruhr Valley with a new secret weapon, a highly destructive ‘bouncing bomb’.

A black and white picture of a Dam with trees in the foreground and fields in the background.
The massive Möhne Dam pictured before the Second World War (1939 to 1945).  This curved gravity dam, held in place by its own weight, whose waters generated electricity, was 40 metres high and 650 metres long. It was the key targeted dam, along with the Eder Dam which supplied water to canals and waterways, and the earthen Sorpe Dam. © IWM. CH9679.

The aim was to cause catastrophic flooding in the enemy’s industrial heartland, sabotaging war production and destroying infrastructure. 

The raid was celebrated as a significant military success by the Allies at the time, a powerful morale booster, but it came at great cost to human life. 53 aircrew were killed and an estimated 1,300 people drowned or were missing when the breached dams inundated a 65 kilometres stretch of the surrounding area.

Hundreds of properties were destroyed and thousands of livestock lost.

The background

The Ruhr Valley, with its armaments factories, power plants and other industrial sites, was at the heart of the German war machine and a priority target.

A report promoted, and initially rejected, within the RAF was that to breach the largest dam, the Möhne, a low-flying aircraft would have to release a huge bomb that would hit the dam, sink and explode against it deep underwater.

The problem was that there was no such bomb and, in any case, the necessary size of such a bomb would exceed any of the RAF’s existing aircrafts’ payload.

If this strategy were to be considered, a revolutionary new type of weapon would have to be developed.

Dr Barnes Wallis and experiments with bouncing marbles

Barnes Wallis was known for thinking out of the box; developing innovative concepts in his spare time that might help the war effort.

A black and white portrait of Dr Barnes Wallis, wearing a suit, shirt and tie.
British engineer, Dr Barnes Wallis (1887 to 1979), was Assistant Chief Designer at the Aviation Section of aircraft and munitions manufacturer, Vickers-Armstrong, where he had worked on the design of the R100 airship and the Wellington bomber. To destroy the Möhne Dam, he originally set about designing a huge six-engine bomber that would drop a 10 tonne bomb on the dam from 40,000 feet creating an earthquake effect.  But it was soon realised that even this enormous explosive force would not breach the dam. © IWM. HU92132.

He later said in a 1973 autobiographical article:

‘I had the idea of a missile which, if dropped on the water at a considerable distance upstream of the dam, would reach the dam in a series of ricochets, and after impact against the dam would sink in close contact with the upstream face of the masonry.’

Dr Barnes Wallis

He first experimented with the idea in his own back garden using his daughter’s marbles, firing them from a home-made catapult and making them bounce across butts of water.

Early experiments and the bouncing bomb

Barnes Wallis experimented with different methods of attacking the dams, including using a scale model replica of the Möhne Dam, as well as carrying out tests in the large indoor water tanks at the National Physical Laboratory, Teddington, South-West London.

A close-up black and white image of a Dam. Water can be seen on the right hand side with a curved wall in the middle.
Replica of the Möhne Dam, built to a scale of 1:50, in the grounds of the Building Research Establishment at its Garston site, Hertfordshire. Scheduled Monument. © IWM. C(AM) 1603.

Eventually, having proved to the Ministry of Aircraft Production that his concept of a bouncing bomb was the best method of attack, experimental barrel-shaped bombs were dropped from a Wellington aircraft at Chesil Beach from December 1942 into early 1943.

A black and white image of a beach. The shot is taken from above with the sea to the right hand side and fields and houses to the left and in the distance.
Chesil Beach, Dorset, photographed in 1970. Source: Historic England Archive. JEH 22044 022.

In these filmed trials, the bombs initially shattered on impact with the water, but Barnes Wallis made many modifications, including adding a backspin on the bomb which improved its bouncing ability.

In subsequent trials, the bomb bounced more than twenty times and travelled over 1,200 metres.

The bouncing bomb gets the green light and undergoes further trials

To successfully breach the Möhne Dam, the bombers would have to fly at a precise tree top-brushing altitude of 60 foot (18 metres) at a speed of 232 mph, before dropping the spinning four tonne bomb at exactly 1,276 foot (389 metres) from the dam. The correct distance would be judged using a simple wooden triangular sight focused on the dam’s twin turrets, and the accurate height ascertained from two intersecting spotlights under the aircraft.

A diagram showing the dam with searchlights and flak coming out of the top and a bomb being released from a plane, showing how it would crash into the dam.
Diagram showing how the bouncing bomb would work.  It was codenamed ‘Upkeep.’ © IWM.

The 1.5 metre long bomb would use its reverse spin to bounce across the water surface towards the dam wall, avoiding the torpedo nets.  When the bomb hit the structure, the backspin would force it downwards deep underwater where it would explode like a depth charge, breaching the dam. 

A black and white shot of the bomb mid-air above the sea with waves behind it from where it bounced on the sea.
A practice bouncing bomb. © IWM. FLM 2342.

At the start of 1943, Barnes Wallis showed the Chesil Beach films to the Air Ministry and to the Ministry of Aircraft Production.  Full scale trials were approved, despite opposition from his employers at Vickers-Armstrong (‘silly nonsense’) and Bomber Command’s Air Chief Marshall Sir Arthur ‘Bomber’ Harris (1892 to 1984) who called the idea ‘tripe of the wildest description’.  

A black and white photograph showing another angle of the bomb mid-air above the sea with waves behind it from where it bounced on the sea. There are people standing on the shore in the foreground.
Film still showing the bouncing bomb during secret trials on the Thames Estuary at Reculver, Kent, 21 April to 1 May 1943.  Barnes Wallis stands on the extreme left of the observer group. These bouncing bombs, dropped by a modified Lancaster bomber, were steel cylinders with wooden casings.  The wood initially broke away on impact and it was decided to dispense with the casings. © IWM. FLM 2343.

The top brass had determined that the best time for a strategic attack on the Ruhr dams was on a moonlit night before the end of May 1943 when the reservoirs were at their fullest.  This pressurised timetable meant the trials would be still running right up until that date. 

Crack new air squadron formed

At the end of February 1943, while trials of the bouncing bomb were still underway, a crack Squadron of highly experienced pilots and aircrew, based at RAF Scampton in Lincolnshire, was established specifically for the attack on the dams. Hangar 2, where 617 Squadron was housed and where Guy Gibson had his office, is Listed Grade II. 

A black and white image of Guy Gibson holding gloves in his hand. A plane can be seen behind him.
Wing Commander Guy Gibson (1918 to 1944) was appointed commander of the new 617 Squadron. Bomber Command’s ‘Bomber’ Harris had been tasked to form the Squadron, having initially been fiercely opposed to the use of his aircraft.  At 25, Gibson was already a veteran of over 170 sorties into enemy territory. © IWM. CH11047.

The Squadron later became known as the ‘Dambusters.’

The highly secret mission was codenamed ‘Operation Chastise.’

A black and white photograph showing a close up of the dam. Water can be seen in the foreground with two brick towers at either end. Trees and a grassy hill can be seen in the distance.
The Derwent Reservoir Dam, one of the locations chosen for the Lancaster bombers’ practice flights as the dam resembled those targeted in Germany’s Ruhr Valley. Just before the Operation Chastise, aircrew examined scale models of the German dams. Source: Creative Commons.

The Squadron started daily intensive training in modified Lancaster bombers, practising low level night flying and navigation, over bodies of water and canal systems, criss-crossing the country, including Scotland. Dummy practice bombs were dropped on different reservoirs. 

None of the aircrews as yet knew the reason for these operations.

A black and white photograph close up of the plane carrying the bomb which is attached to the bottom of the plane.
The barrel-shaped Upkeep bomb attached to the bomb bay of a modified Lancaster. To the right is the reverse spinning mechanism. © IWM. 69915.

On 11 April 1943, all personnel involved in the operation received a high security briefing at RAF Manston, Kent. 

Guy Gibson and his Bomber Leader, Flight Lieutenant Bob Hay, were ordered to Reculver to witness the secret trials of the new bomb, before 617 Squadron practised dropping dummy Upkeeps there. 

On 14 May, the Squadron’s Lancaster’s took part in a full dress rehearsal on Uppingham Lake, Rutland and Colchester Reservoir in Essex.

Bomber Command was given the final go-ahead by the Air Ministry on 15 May:  Operation Chastise would begin the following day.

Operation Chastise

At 9.28pm on 16 May 1943, on a bright moonlit night, nineteen Lancaster bombers took off in three waves at ten minute intervals from RAF Scampton. 133 airmen were on board. They flew low over Europe to avoid radar detection.

Gibson led the first attack wave, releasing the bouncing bombs on the massive Möhne Dam while under attack from flak gunners in the dam towers.

A black and white photograph showing planes with bombs lined up on a runway.
Lancaster bombers photographed in 1943. © IWM. CH8646.
A black and white photograph of an aerial shot of a dam with damage to the middle of the wall.  Fields and trees can be seen in the foreground with water on the right hand side and at the back behind the wall.
The destroyed Möhne Dam, the biggest of the Ruhr Valley dams, showing the extensive flooding. This aerial image was taken by an RAF photo-reconnaissance Spitfire at first light on the morning following the attack. The enormous rupture was over 75 metres across and 22 metres deep. Source: Public Domain.

Four aircraft dropped bombs, but it was not until the fifth attack that the dam was fully breached.  

As the dam burst, a colossal wave of water, estimated at 10 metres high and travelling at 24 kilometres an hour, swept across the Ruhr Valley destroying everything in its path.

A black and white image showing the destruction after the dam was breached.
Pictured is the widespread destruction after the Möhne Dam was breached. Source: Public Domain.

The remaining aircraft breached the Eder Dam after several unsuccessful attempts. It had been shrouded in fog but was undefended. The earthen Sorpe Dam remained intact. German night fighters were scrambled to try and thwart attacks, without success.

The last Lancaster landed back at base at RAF Scampton at just after 4am on 17 May, seven hours after the mission began.

Eight aircraft out of nineteen failed to return and 53 of the 133 aircrew were lost.  Three others were captured and became prisoners-of-war.

A black and white image showing rows of coffins with wreaths on top.
Mass burial of victims of the flood. Source: Public Domain.

In the Ruhr Valley, the catastrophic flooding spread over 65 kilometres. An estimated 1,300 people drowned or were missing, including prisoners-of-war and forced labourers incarcerated in camps, hundreds of whom were women from Ukraine, Poland and Russia. The attack caused more civilian deaths than in any previous RAF attack on Germany during the war.

Factories, power plants, mines, roads and bridges, homes and other properties were destroyed; agricultural land inundated and ruined; animals lost.


The Dambusters’ mission raised British morale. The press was triumphalist: 617 Squadron were heroes (617 later became a specialist precision bombing Squadron). Gibson was awarded the Victoria Cross. 32 other aircrew also received honours. 

A black and white image showing men in military uniform standing in a field with an aircraft behind them.
King George V1 visiting RAF Scampton 10 days after the Dambusters’ raid, 27 May 1943. Guy Gibson, with his back to the camera, is shown introducing his Squadron to the King who stands to his right.  A Lancaster aircraft is in the background. © IWM. TR1003.

German morale took a battering, but industry in the Ruhr Valley was up-and-running again within a few months; an estimated 30,000 workers had been commandeered to repair the damage.

Although only two dams were breached, Operation Chastise did handicap the German war effort by the need to divert valuable resources to the area in terms of workers and anti-aircraft batteries, particularly from the Eastern Front where Germany was heavily engaged fighting the Soviet Union.

Barnes Wallis Wallis himself was appalled by the RAF casualties. He had been awarded £10,000 for his war work. In 1951, he donated the money towards a fund to help with the education of children of RAF personnel.

A black and white photograph showing a group of men gathered around a table signing a document.
Signing the Additional Protocols to the Geneva Convention, 8 June 1977: international treaties that contain rules limiting the barbarity of war and protecting non-combatants. Source: Public Domain.

In 1977, the Additional Protocols 1 and II of the Geneva Convention included outlawing attacks on dams.


There are a number of memorials to the Dambusters’ raid and associated crash sites, both in Britain, the Netherlands, Germany and elsewhere.

A large memorial with names inscribed and large inscription in the middle. There are wreaths and flowers on the floor in front.
617 Squadron Memorial, Woodhall Spa, Lincolnshire. RAF Woodhall Spa was the Squadron’s last airbase during the Second World War. The memorial is in the form of a dam with its breach represented by a central leaning slab of slate which is incised with the names of the Squadron’s missions. Source: Creative Commons.

The memorial pictured commemorates, in alphabetical order without rank but with individual honours listed, the 204 aircrew of 617 Squadron who lost their lives in different missions during the Second World War, including the 53 killed during Operation Chastise. 

The inscription running across the top reads: ‘They Died for Your Freedom.’

A plaque with '17. MAI 1943' written at the top an drawings of two planes dropping bombs on the dam. There is water flowing through the middle showing people, animals and buildings.
A plaque memorialising the attack on the Möhne Dam, Wickede, Germany, showing drowning people and animals, and washed-away buildings.  It was inaugurated in 2015. Source: Creative Commons.

The memorial information tells the story of the Dambusters’ raid and the rebuilding of the dam, in German and English, remembering the victims of what is known there as the ‘Möhne Catastrophe’.

A small grey memorial with and plaque showing some inscription. There are four poppy wreaths sat in front.
Memorial to the seven aircrew of one of the second wave of Dambuster Lancasters, piloted by Squadron Leader HM Young, shot down while crossing the coast at Castricum-ann-Zee, Netherlands.  The memorial is located there. None of the aircrew survived. Source: Creative Commons.

The plaque reads: ‘On the night of 16/17 May 1943 Lancaster AJ-A was on the homeward flight from a raid on the German dams (Operation Chastise) to RAF Scampton. The Lancaster was hit by anti-aircraft fire and crashed about 2km south from this point along the shoreline.’

Two headstone with inscriptions and bright flowers surrounding.
The graves of Wing Commander Guy Gibson and Squadron Leader Jim Warwick, Steenbergen, Netherlands. Source: Public Domain.

In the year following the Dambuster operation, on 19 September 1944, Gibson and his navigator Warwick were flying in a Mosquito as part of an attack on Germany. It was thought that they may have had engine problems. Their aircraft crashed around 10.30pm. Neither man survived.

The Dutch authorities laid them to rest in a local cemetery. Later the Commonwealth War Graves Commission replaced their crosses with standard headstones.

A photograph of a gravestone.
Grave of Barnes Wallis in his local church of St Lawrence, Effingham, Surrey.  The Latin inscription means ‘Severed from the earth with fleeting wing.’ Source: Creative Commons.

During the Second World War, Barnes Wallis also developed the enormous ‘Tallboy’ bomb used to sink the battleship, Tirpitz, flagship of the German fleet, and attack V1 rocket launch sites and U-Boat pens.

After the war, Barnes Wallis continued to lead aeronautical research and development. In 1954, he became a Fellow of the Royal Society and was knighted in 1968.

An image of a badge with a crown at the top and and blue circle with gold edges underneath with and image of the dam in the middle. 'Squadron' is written at the top, '617' on both sides and 'Royal Air Force' at the bottom. There is writing below this which reads 'APRES MOI LE DELUGE'
Badge of 617 Squadron.  The design, with its motto in French, ‘Apres Moi Le Deluge’ (After me, the flood) and a representation of breached dam, was approved by the King. Source: Public Domain.

The last surviving member of 617 Squadron, Johnny Johnson, died in 2022 aged 101.

Written by Nicky Hughes.

Banner image: Illustration showing Lancaster bombers attacking the Möhne Dam, Germany, on the night of 16 and 17 May 1943. Source: Creative Commons.

Further reading

4 comments on “The Story of the Dambusters: Operation Chastise, May 1943

  1. W.O. Hofstede

    The correct spelling of the Dutch location is Castricum-aan-Zee.

  2. The authorities were well aware that over 1000 civilians would be killed in the subsequent flood. Within 6 months the dams were rebuilt. Bomber Harris publicly stated that the breaching of the dams made no difference to the tide of the war. What a terrible waste of good young lives.

  3. Joanne Harris

    Barnes Wallis is us buried in Effingham SURREY not Suffolk

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