The Dambusters Raid over the night of 16/17 May 1943 is rightly considered to rank among the most dangerous, most daring and most ingenious operations of the entire Second World War. 70 years on from the day itself, the Royal Air Force will commemorate Operation Chastise with a series of flypasts.  This article serves as an introduction to GAR’s coverage of those events.

Conceived by legendary English scientist, engineer and inventor Professor Barnes Wallis, Operation Chastise – as the raid was officially known – sought to bring Germany to its knees by crippling its industrial heartland, in this case the Ruhr Valley.

© Karl Drage -

In 1939 Wallis had himself noted that through the use of strategic bombing against key targets, one could “render the enemy utterly incapable of continuing to prosecute the war.”

Wallis’ vision required the use of huge bombs that could concentrate their force and destroy targets that were otherwise unlikely to be affected by existing munitions, and he set about designing both the weapons and vehicles to achieve this.  The first targets that were identified as being of particular interest were Germany’s shipping, but, soon after, focus fell on the hydro-electric dams used in the steel-making industry, for the supply of drinking water and also for ensuring that there was a sufficient volume of water for the canal transport system to function properly.

It was in 1942 that Wallis began to experiment with the idea that would ultimately be used in Operation Chastise, initially by making marbles skip over water tanks in his garden.  Wallis’ paper “Spherical Bomb – Surface Torpedo” concluded that if a drum-shaped bomb could skip over the surface of the water (thus avoiding nets that had been positioned to catch torpedoes) and sink next to a battleship or a dam wall, the surrounding water could be used to concentrate the force of the explosion on to the target.

© Karl Drage -

Furthermore, Wallis’ realisation that if the bomb had backspin imparted upon it, it would have improved stability in flight, would trail behind the aircraft delivering it (increasing the aircraft’s chances of surviving the ensuing detonation unscathed), would travel further and also prevent it from moving a significant distance away from the dam wall as it sank.  It also meant that the timing of the detonation could be determined in advance, using a hydrostatic pistol, as with a regular naval depth charge.

Certain elements within the Royal Air Force took a great deal of persuading before it finally decided to adopt Barnes Wallis’ incredible ‘bouncing bomb’ idea, codenamed “Upkeep”.

Testing of Upkeep began in December 1942 when a Vickers Wellington flying from RAF Warmwell dropped an inert prototype at Chesil Beach in Dorset.  The weight and physical size of a real, live bomb meant that it could only be carried in the bomb bay of a significantly modified Avro Lancaster, dubbed the B Mark III Special (Type 464 Provisioning).  Indeed, the Lancasters in question had much of their internal armour removed to reduce weight, as well as the mid-upper machine gun turret, and, due to the shape of their payload, the bomb-bay doors were also removed, leaving a significant portion of the Upkeep weapons visible beneath the aircraft.

Guy Gibson's modified Lancaster B.I, ED825/G, pictured with and without the special 'Upkeep' weapon designed by Barnes Wallis and used by 617 Squadron to attack dams in the Ruhr industrial heartland of Germany on 16/17 May 1943 © Crown Copyright

On 26 February 1943, Chief of the Air Staff, Air Chief Marshal Charles Portal ordered that 30 Lancasters be allocated to the mission and set a target date of May, when it was known that water levels would be at their peak and damage inflicted from striking the dams would be at its greatest.

No. 617 Squadron was formed at RAF Scampton on 21 March 1943 under a veil of secrecy, initially as Squadron X, with Wing Commander Guy Gibson, a 24 year old with over 170 bombing and night-fighter missions behind him, as the Officer Commanding.  Although Gibson was unaware of it at the time, the squadron was formed with the specific task of attacking the Möhne, Sorpe and Eder dams in the Ruhr area, and Gibson hand-picked 21 existing Lancaster crews from other squadrons of No 5 Group to carry out this mission.  The nature of the weapon they would be using necessitated the development of a new range of tactics in order to successfully deploy Wallis’ invention, and Gibson and his men had only a matter of weeks in which to devise and perfect these techniques.

Wing Commander Guy Gibson, the Commanding Officer of 617 Squadron, pictured in the Summer of 1943 © Crown Copyright

Wallis had concluded that in order to be at its most effective, Upkeep needed to be released head-on to the target, from a height of just 60 feet and at an air speed of 240mph – an extreme challenge for the crews who had only unreliable barometric altimeters to use for altitude information, aside from the fact that 60 feet was unnaturally low, especially for an aircraft the size of a Lancaster.  A simple yet hugely effective way of verifying their height was therefore devised, by mounting two spotlights on the aircraft, one under the nose and one under the fuselage, just behind the bomb bay.  When the two beams of light converged on the surface of the water, the crews knew that they were at the correct height.

Even with this tool at their disposal, it still required great airmanship to fly accurately so low, and 617 Squadron’s crews spent the bulk of the short amount of time they had been afforded working on their low-level and night-flying skills over water, with the reservoirs at Derwent, Abberton (near Colchester) and Eyebrook (then known as Uppingham), and the Wash weapons ranges, being the particular venues of choice.

As the night of the raid grew closer, it was at Abberton and Eyebrook that these skills were really honed.

From mid-April, Eyebrook was predominantly used at night and local legend has it that the residents often thought they were under attack themselves, and Flight Lieutenant Dave Shannon, the captain of AJ – L (‘L for Leather’ on the raid itself) recalled how, when it came to practising flying this low, “Eyebrook Dam was much favoured.”

While the dam at Eyebrook most closely resembled the Sorpe Dam, the Corby and Northants District Water Company gave permission for scaffolding to be erected on the dam wall and covered with hessian in an attempt to better prepare the crews for what the dams at Eder and Möhne actually looked like.

Of the four training sites, only Derwent and the Wash ranges saw bomb releases against targets positioned on the water, while Eyebrook was predominantly used to test sighting methods.

Members of 617 Squadron photographed at Scampton after the Dams raid in May 1943 © Crown Copyright

Another problem that needed to be resolved concerned the optimal distance from the target at which to release the bomb, and a number of targeting tools – such as utilising a coat-hanger, string and the bomb-aimer’s glass dome – were devised to assist the bomb aimers, though there remains some conjecture over precisely which were employed on the night itself.

An early release would cause the bomb to fall short, and the water between the detonation and dam wall would act as a cushion, absorbing the power of the explosion, while a late release would see the bomb overshoot and explode in the open, taking the aircraft with it.

Just five days before the raid, 617 Squadron started to train with inert Upkeep bombs at Reculver on the Kent coast and the crews were said to be amazed to see the drums bouncing over the sea to the beach.  Even at this late stage, nobody on the squadron knew what their targets would be and speculation that it might be the Tirpitz started once again.

Two nights before the raid, on 14 May, the reservoirs at Eyebrook and Abberton bore witness to full dress rehearsals of the mission, but it was only the next day when Gibson was finally made aware of the task that lay ahead of him and his men.

Operation Chastise itself took place on the night of 16/17 May when a total of 19 Lancasters took off from RAF Scampton in three waves.  Formation No.1 was made up of nine aircraft and was led by Gibson himself, taking off at 2139 local in aircraft ‘G for George’. Its mission was to attack the Möhne Dam, and any aircraft with bombs remaining after it had been successfully breached would continue on to attack the Eder.  The second and third formations each comprised five aircraft.  Formation No. 2 was assigned with the task of attacking the Sorpe Dam, and the first two formations’ flightpaths were choreographed to ensure they crossed the enemy coastline simultaneously.  Formation No.2 actually took off ahead of Formation No. 1, with Flt Lt Bob Barlow (RAAF) in ‘E for Easy’ getting airborne first at 2128 local.  If any aircraft had weapons on-board after the Sorpe had been breached, they had three further secondary targets that they could move on to, namely the dams at Lister, Ennepe and Diemel. Formation No. 3 departed two hours later and was a mobile reserve, charged with attacking either the primary targets, if any had not been breached, or the secondary targets.  In the event that all had been breached by the time Formation No. 3 reached the Dutch coast, they would be recalled.

Leader of the Dambusters Raid, Wing Commander Guy Gibson, seen with his crew as they board their Avro Lancaster III ED932/AJ-G for the Dams' Raid of 16/17 May 1943. L-R: Flight Lieutenant RD Trevor-Roper, Sergeant J Pulford, Flight Sergeant GA Deering (Canadian), Pilot Officer FM Spafford (Australian), Flight Lieutenant REG Hutchison, Wing Commander Guy Gibson, Pilot Officer HT Taerum (Canadian) © Crown Copyright

Eight of the 19 aircraft that had set out – including four out of five from Formation No. 2 – failed to reach their targets, either as a result of crashing or being forced to turn back for various reasons.  As an indication of precisely how low they’d been flying (100ft was the planned altitude to avoid radar detection), one aircraft briefly dipped its belly into the sea, lost its Upkeep but still recovered to Scampton, while a further two are said to have struck electricity wires and pylons and crashed en-route.

The fourth and fifth remaining aircraft in Formation No. 1 each struck the Möhne Dam, with the bomb from the aircraft piloted by Flt Lt David Maltby (‘J for Johnny’) resulting in a large breach.  Gibson then led four other aircraft – three with weapons still on-board – to attack the Eder Dam, with the third weapon release (second hit) – from aircraft ‘N for Nancy’, piloted by Flying Officer Les Knight (RAAF) – causing a large breach.

Of Formation No. 2, only ‘T for Tommy’, piloted by Flt Lt Joe McCarthy (an American serving in the RCAF), managed to attack the Sorpe.  While the dam was hit, only a largely insignificant breach was achieved.  McCarthy was just 20 minutes from home when he finally transmitted the message “Goner 79C – Weapon release at the Sorpe dam, exploded on contact with the dam and a small breach made.”  As a consequence of this delay, and despite the fact a primary target remained intact, the two surviving aircraft of Formation No. 3 were directed against secondary targets, which they both hit but without breaches achieved.

One aircraft from Formation No. 1 was shot down whilst attacking its target as were two others on the return journey, including ‘A for Apple’, flown by Sqn Ldr H M Young, which had been the first aircraft to successfully strike the Möhne Dam, causing a small breach.

In total, eight aircraft failed to return from Operation Chastise, with the resultant loss of 53 of the 133 aircrew who had participated in the raid.  A further three were captured as prisoners of war after baling out of stricken aircraft.

The damage inflicted on the dam at Möhne resulted in the release of 330 million tons of water into the western Ruhr region.  A small number of mines were flooded and 11 small factories and 92 houses were destroyed.  A further 114 factories and 971 houses were damaged. Floodwater washed away about 25 roads, railways and bridges as it spread over a distance of around 50 miles from the source.  It is estimated that before 15 May 1943 water production on the Ruhr was one million tonnes and that this dropped to just 250,000 tonnes immediately after the raid.

Aerial reconnaissance photograph taken on 17 May 1943 showing the breach in the Mohne Dam caused by 617 Squadron's raid during the previous night. The Eder Dam was breached by means of 'bouncing bombs' designed by Barnes Wallis. This spectacular feat of precision bombing had tremendous propaganda value, although its practical effects were less great than many had hoped © Crown Copyright

The greatest impact on the Ruhr’s armament production was brought by the loss of hydro-electric power. Two powerplants (producing 5,100 kilowatts) associated with the dam were destroyed and seven others were damaged.  Many households in the area were also without power for a period of two weeks.

Despite Barnes Wallis’ claims after the raid that, “I feel a blow has been struck at Germany from which she cannot recover for several years,” water output and electricity production had returned to their previous levels inside six weeks.

While Operation Chastise perhaps did not cripple the German wartime effort in quite the way envisaged, the images of badly scarred dams served as a real fillip to the Allies who were still on the receiving end of heavy German bombing raids.

GAR Editor Gareth Stringer spoke to TV presenter and historian Dan Snow about the impact the raid had had on World War 2 at the Dambusters 70th official unveiling event at RAF Coningsby in March of this year:

“The raid worked on many levels. Firstly there was the damage done, which was significant, and while it didn’t bring the War to an end, there was an effect on production of steel and raw materials in Germany.

“But, more importantly, the Second World War was a people’s war; it was a war of media, of press, and of spin and propaganda. The Dambusters Raid made people believe that the Allies could take the battle to the heart of Hitler’s Germany, and in 1943 that was still a surprising thing.

“People say, ‘It was only a propaganda victory’, but you know what, that is still a victory, and we know from subsequent conflicts, like Vietnam and Iraq, that what the public think is almost as important as what is actually happening on the ground.”

Gibson, for his role in leading 617 Squadron, was awarded the Victoria Cross to go with bars to both Distinguished Service Orders (DSOs) and Distinguished Flying Crosses (DFCs) received earlier in the war.  He was later killed in a Mosquito accident on 19 September 1944, the cause of which remains unclear.

Wing Commander Guy Penrose Gibson VC DSO* DFC*. Portrait taken for the book "Air Aces" by Gordon Anthony first published in 1944 © Crown Copyright

However you look at it, what was achieved by The Dambusters on that fateful night will forever be enshrined in the history books as the successful execution of a truly remarkable mission, in extraordinarily trying conditions.