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The Dam Busters 75 years on: how Operation Chastise was planned and executed

The Dam Busters 75 years on: how Operation Chastise was planned and executed

As well as being the RAF’s Centenary year, 2018 also marks the 75th anniversary of what is probably the RAF’s most famous mission of World War 2: ‘Operation Chastise’ - the Dams Raid. Here we tell the story of this audacious attack on Germany’s industrial heartland.   

During World War 2  the Ruhr Valley was often targeted by the Allies because as a major industrial centre, it was key to the German war effort.  It was however heavily defended and allied bomber losses were high, earning it the ironic nickname ‘Happy Valley’ amongst RAF aircrews. 

Whilst conventional raids could wreak significant damage to targets such as factories and mar-shalling yards, the dams of the Ruhr Valley were largely immune to attack because they presented a difficult target to hit with bombs dropped vertically from high altitude. 

The strategic significance of the dams had been recognised by the British Air Ministry in the run up to war. The dams provided hydro-electric power, plus water for manufacturing, drinking and maintaining canals.  

But it really wasn’t until 1943 that the British possessed the means to attack the dams success-fully - albeit in a manner that was extremely risky and required a huge amount of skill on the part of the aircrews involved.

Dam-busting innovation

Barnes Wallis, a scientist and engineer who had previously pioneered the use of geodetic design principles in airframe manufacture, developed the concept of a ‘bouncing bomb’ - a depth charge that when released from a low flying aircraft, could skip over water, avoiding torpedo nets, to then sink next to a ship or indeed a dam wall. 

Fitted with a hydrostatic fuse, it would then blow up at a pre-determined depth with devastating effect, the surrounding water helping to concentrate the force of the blast.  

By applying backspin to the bomb prior to release, it was prevented from moving away from the wall as it sank.  The weapon, weighing 4,200 kg, was given the codename ‘Upkeep’.     

The other technological innovation that made an attack on the dams possible in 1943 was the Avro Lancaster bomber, a very capable aircraft that had entered service with the RAF the previous year and was fast becoming Britain’s principle heavy bomber. 

The Lancaster had the requisite versatility and performance to undertake the mission but still had to be specially modified for the task. The doors of the cavernous bomb bay were removed and fairings were fitted at either end.  

Special struts were provided to suspend the bomb under the aircraft and a mechanism was in-stalled to provide the necessary rotation of the bomb prior to its release.  

The mid-upper gun turret was removed to save weight. A larger bomb aimer's blister was fitted and the normal bombsight was replaced with a purpose-built, but very simple, aiming device. 

Two powerful lamps were also provided, one under the nose the other under the fuselage, their beams set to converge on the surface of the water when the aircraft was flying at exactly 60 feet - the optimal height for release of the weapon.

The Dam Busters 75 years on: how Operation Chastise was planned and executed

Birth of ‘The Dam Busters’

On 21st March 1943 a special squadron was formed to undertake the mission - No. 617 based at RAF Scampton in Lincolnshire and led by 24 year old Wing Commander Guy Gibson. 

The elite aircrews - consisting of Australians, Canadians and New Zealanders as well as British personnel -  practised flying at night and at very low level.  

The Derwent Reservoir in Derbyshire was one of several English reservoirs over which training flights took place, the Derwent Dam being similar in layout to the German dams.

The Raid

Finally on the evening of 16th May 1943, two separate formations took off from Scampton bound for the Ruhr, using two routes that avoided known enemy anti-aircraft batteries. 

A third, reserve, formation took off just after midnight. The aircraft flew at very low level (some-times less than 30 metres above the ground) to avoid German radar. 

Formation No.1 headed for the Mohne Dam, with instructions to then attack the Edersee Dam on the River Eder if they had any bouncing bombs left over.  

The smaller Formation No. 2 headed for the Sorpe Dam. Unfortunately only one aircraft from For-mation No.2 actually made it to the target, so some aircraft from the reserve formation were directed to the Sorpe Dam as well. 

The attack on the Mohne Dam was successful. Three bouncing bombs hit the dam, two of them causing breaches. Gibson then led aircraft that were still carrying their ‘Upkeeps’ to the Edersee Dam, which was shrouded in fog. A single hit caused a large breach.    

The Sorpe Dam was not made of steel and concrete like the Mohne and the Edersee Dams. It was a vast earthen structure in an area were the topography was particularly challenging. 

A different method of attack was therefore required. Each of the three Lancasters that eventually made it to the target approached along the length of the wall rather than across the reservoir. Two bombs hit the dam but there was no breach. 

Another Lancaster from the reserve formation was instructed to attack the Enneppe Dam alt-hough there is some evidence to suggest that this aircraft may have actually attacked the Bever Dam by mistake. In any event, the attack was unsuccessful.  

A Lancaster sent to attack the Lister Dam was shot down en route.  In total, eight Lancasters were lost on the Dambusters raid, and 53 aircrew were killed.     


The Mohne Dam breech sent a 10 metre high wave down the valley below, destroying buildings, roads and railways over a distance of 80 kilometres. 

Almost 1600 people were killed, a significant proportion of whom were prisoners of war and forced labourers from the Soviet Union. 

In the case the Edersee Dam, a 6-8 metre high wave travelled 30 Kilometres downstream and claimed 70 lives.
The overall impact of the raid remains a matter of some debate. The raid did cause a lot of damage to German infrastructure, disrupted hydroelectric power generation, reduced the amount of water and coal available for industrial use, and led to a drop in food production. 

But the Germans repaired the dams in just 5 months before the rainfall of autumn, albeit by diverting labour resources from the construction of the Atlantic Wall. Had the Sorpe Dam also been breeched (and it very nearly was) it would have been harder to recover as quickly. 

However, the raid was undoubtedly a major Allied propaganda victory, and created a legend that endures to this day.     

Dams Raid Key Facts

Dams Raid Key Facts      

  • The standard radio telephone sets used on Lancasters were not deemed good enough for the level of communication required between aircraft on the mission, so were replaced with the best VHF sets then available to the RAF
  • The mission was planned so as to coincide with the time of year when the reservoirs were at their fullest.       
  • Lancasters flew so low on the mission that a bomb was lost from one aircraft when it clipped the sea, and two aircraft crashed after hitting power lines. 
  • Gibson was awarded the Victoria Cross and 29 other medals were awarded to aircrew who took part in the mission.
  • There is a commemorative plaque to 617 Squadron on the Derwent Reservoir dam
  • The 617 Squadron badge features a breeched dam graphic 

For more information, check out these Haynes publications: Avro Lancaster Owners Workshop Manual and Royal Air Force 100 Technical Innovations Manual.