Dambusters 70th anniversary: How the daring mission unfolded

In May 1943 19 aircraft, crewed by 133 young men, took off on one of the most daring wartime missions that has now become one of the most well-known.

Here is an overview of how the mission came about and how it was executed:

The idea
The plan for the Dambusters raid originated early in the Second World War - some sources cite as early as 1940 - when aeronautical engineer Dr Barnes Wallis, proposing the use of a 10 ton bomb from an altitude of about 40,000 ft on German dams, was forced to re-think as no bomber aircraft was capable at the time of flying at that altitude with such a heavy payload.

He realised a much smaller explosive charge would suffice, if it could be exploded directly against the dam wall below the surface of the water, but the major German reservoir dams were protected by heavy torpedo nets to prevent such an attack.


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With a team at Vickers, Wallis designed the 'bouncing bomb', a missile that would skip across the water, hit the dam and roll to the bottom.

It needed to be dropped at the right height, the right speed and the right distance so it would skim for a significant distance over the surface of the water in a series of bounces before reaching the dam wall.

Its residual spin would run the bomb down the side of the dam to its underwater base. Using a hydrostatic fuse, an accurate drop could bypass the dam's defences and enable the bomb to explode against the dam.

March, 1941
Wallis researches, writes and circulates a paper entitled "A Note on the Methods of Attacking the Axis Powers" among military and political circles. The outcome is the formation of the 'Aerial Attacks on Dams Committee' to take his suggestions further.

February 26, 1943
Wallis' idea was put forward to Bomber Command and after several conferences was accepted. While Wallis' team worked to perfect the 'Upkeep' bomb design, Bomber Command assigned the mission to 5 Group.

March, 1943
For the mission, named Operation Chastise, a new unit, 617 Squadron, was formed with 24-year-old Wing Commander Guy Gibson in command and based at RAF Scampton, just north-west of Lincoln.
Even Gibson, a veteran of over 170 bombing and night-fighter missions, did not know the reason behind the formation of this squadron. His task was to mould and train the crew members, volunteers all into a squadron capable of carrying out a difficult single raid.

He was soon to find out what his targets were to be, to divert attention away from the truth. A rumour was started that the aircraft were about to attack the Tirpitz battleship.

The new 617 squadron began training, which was to consist of flying and navigating at zero feet. They then switched to flying over water. This created its own problems for the pilots, who complained they could not judge height over water.

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Gibson's men began test runs over reservoirs around England, including the Derwent Valley.

Many problems were encountered, and practice runs at Reculver Bay continued using the test Upkeep bombs. Finally everything came together and a date was set for the full moon on May 16/17.

Only on the eleventh hour did any of the crews find out what the real targets were. They were charged with flying across the English channel, to cross the Netherlands and Germany at zero feet and to drop a bomb on the Ruhr dams.

May 13, 1943
Following their final testing, the Upkeep bombs were delivered, with the goal of Gibson's men conducting the mission four days later.


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May 16, 1943
A total of 19 aircraft set out at dark; nine were to attack the the Mohne dam, then proceed to the Eder; five were to attack the Sorpe; and five constituted a 'flying reserve'.

Gibson's crews flew at around 100 feet to evade German radar. On the outbound flight Gibson's Formation 1, consisting of nine Lancasters, lost an aircraft en route to the Mohne when it was downed by high tension wires.

Gibson led the attack on the Mohne dam and successfully released his bomb.
He was followed by Flight Lieutenant John Hopgood whose bomber was caught in the blast from its bomb and crashed.

To support his pilots, Gibson circled back to draw German flak while the others attacked. Following a successful run by Flight Lieutenant Harold Martin, Squadron Leader Henry Young was able to breach the dam.

With the Mohne Dam broken, Gibson led the flight to Eder where his three remaining aircraft negotiated tricky terrain to score hits on the dam. The dam was finally opened by Pilot Officer Leslie Knight.

While Formation 1 was achieving success, Formation 2 and its reinforcements continued to struggle.

Unlike Mohne and Eder, the Sorpe Dam was earthen rather than masonry. Due to increasing fog and as the dam was undefended, Flight Lieutenant Joseph McCarthy from Formation 2, was able to make 10 runs before releasing his bomb.

Scoring a hit, the bomb only damaged the crest of the dam.

Two aircraft from Formation 3 attacked as well, but were unable to inflict substantial damage. The remaining two reserve aircraft were directed to secondary targets at Ennepe and Lister. While Ennepe was unsuccessfully attacked, Lister escaped unharmed as Pilot Officer Warner Ottley was downed en route.

Two additional aircraft were lost during the return flight.

Aftermath
Operation Chastise cost 617 Squadron eight aircraft. A total of 53 airmen, who only had 11 weeks from go-ahead for the project to execution, were killed during the raid and three were made prisoners of war.

The successful attacks on the Mohne and Eder dams released 330 million tons of water into the western Ruhr, reducing water production by 75% and flooding large amounts of farmland.
In addition, over 1,600 were killed though many of these were forced labourers from occupied countries and Soviet prisoners of war.

While British planners were pleased with the results, they were not long lasting. By late June, German engineers had fully restored water production and hydroelectric power.

Though the military benefit was fleeting, the success of the raids provided a boost to British morale and aided Prime Minister Winston Churchill in negotiations with the United States and Soviet Union.

For his role in the mission, Gibson was awarded the Victoria Cross while the men of 617 Squadron received a combined five Distinguished Service Orders, ten Distinguished Flying Crosses and four bars, twelve Distinguished Flying Medals, and two Conspicuous Gallantry Medals.

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