Illustration of how the bomb works


Illustration of how the bomb works
Illustration of how the bomb works

In 1965 the Institution recognised the talent and contribution of Dr Barnes Neville Wallace by awarding him an honorary fellowship. Wallace had achieved something many had thought impossible, even preposterous, and designed not only a bomb that bounced but that sunk at the exact right depth to break the mighty walls of Germany’s Ruhr dams. Wallis was generally regarded as a far-fetched thinker but his tenacity and engineering skills helped to quicken the pace of defeat.

Wallis spent six years developing the ‘bouncing bomb’, favouring the targets as they were immovable and the impact on German production would be severe, causing: disruption steelworks and industry; disruption hydro-electric generation; disruption of supplies to canals, used for transporting arms and good; and disruption to available drinking water.

Bouncing bomb animation
Bouncing bomb animation

However, the dams were so gigantic that the armaments of the time (mostly 500lb bombs and 1000lb general-purpose bombs) would cause hardly a scratch of damage. In 1941 Wallis developed a concept for a “big bomb” (ten-ton bomb, carried by a six-engine Victory bomber and dropped from 40,000ft) to penetrate deep into the ground, causing a shock wave caused by the ensuing explosion. This would create an ‘earthquake’ and shake the target to pieces. This also carried the advantage that the Victory crew did not need a direct hit. However, the RAF had only just begun using 4-engined bombers and the idea of carrying a ten-ton bomb up to 40,000ft seemed fantastical, so his proposals were quickly rejected by the Air Ministry.

Meanwhile, ongoing experiments on the amount of explosives needed to break a dam wall had found that while significant quantities (14 tons) were needed if the explosion was tens of feet away from the dam, as little as under 3 tons would be sufficient if the explosion took place in contact with the wall. Several 1scale models and a disused dam at Nant-y-Gro in Wales were destroyed in arriving at this conclusion. The fact that these tests were mainly performed independently of Wallis’ project reflected the Ministry’s growing faith that the dams could be breached.

Watch the bomb tests

Throughout 1942 Wallis developed the idea of a missile which would be dropped upstream of a dam, ricochet over the water in a series of bounces, and hit the dam. Therefore, it would jump over anti-torpedo nets placed ahead of the dam wall, and would sink right up against the dam. Some initial tests led him to develop a spherical bomb, and full-scale test drops of this design began at Chesil Beach in September, using a modified Wellington bomber. Persuaded by Wallis and films of the test drops, officials gave the go-ahead for further tests which led to the development of two separate variants of the bouncing bomb idea – a large version (codenamed Upkeep) to be carried by the new Lancaster for use against dams (Wallis was confident that if one mine could be dropped in the right place, a dam could be breached) and a smaller one (codenamed Highball) to be carried by Mosquitoes for use against ships. A variety of shapes, drop heights and backspin rotation speeds were tested at Chesil Beach, Reculver and Loch Striven. Of these Highball proved the less effective.

The best time to hit the dams was spring, as they would be fall and therefore the water rush would have a more devastating impact. On 26th February the go-ahead was given to prepare for raid on the Ruhr dams using Upkeep. Twenty-three Lancasters were modified to carry the Upkeep mine (originally a sphere, it was modified to a cylindrical shape during testing). 617 Squadron was formed to perform the mission. Awaiting a full moon, to aid the pilots, 19 Lancasters of the 617 took off from RAF Scampton in three waves to attack the Möhne, Eder and Sorpe Dams. Wing Commander Guy Gibson was the commanding officer for the mission.

The operation was a great technical success, and achieved its principal aims. Two dams were destroyed (more than 116 million m3 of water was released from the Möhne reservoir, 154 million m3 from the Eder), causing widespread damage and destruction up to 100 miles away. 25 bridges were destroyed with an additional 21 damaged, 11 factories were destroyed and 14 damaged, and many coal mines, waterworks, pumping stations and power stations were destroyed or put out of action. Casualties on the ground were upwards of 1300, there were also losses of livestock and agricultural land.

Although it was highly successful in Operation Chastise, Upkeep was never used again in warfare. However, Wallis’s original concept was vindicated.

The bouncing bomb has entered the popular consciousness via the film The Dam Busters and this continues, with a remake planned and a Dambusters App released for the 69th anniversary of the raid. On 4th August 2015, the last of the 19 pilots who flew the bomb died at the age of 96. Squadron Leader Les Munro piloted a Lancaster bomber in Operation Chastise-the Dam Buster mission was one of the most dramatic military actions of the war.

National Archives exhibit

Archive, Institution of Mechanical Engineers


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