1:50 scale Mohne Dam.
Operation Chastise, or the Dambusters raid.
Even before the declaration of World War II, ways were being considered to disable the vast hydro-electric power stations of the Ruhr valley that were known to power the munitions factories in the area. Amongst these was the idea by engineer and aviation designer, Barnes Wallis, to deploy a ten-tonne bomb from 40,000 feet which would bury itself in the ground on impact, with the resulting subterranean explosion causing an ‘earthquake’ that would shatter the vast Mohne and Eder dams. The Air Ministry dismissed this plan, since, at the time, no plane could carry an armament of such weight, and no bomb of such a size could be made.
Undeterred, Barnes Wallis turned his thoughts to attempting to identify the smallest charge that would successfully breach the dams, and to identify the best position to detonate this, relative to the dam itself.
Shortly before WWII, a team of engineering staff from BRS and their work studying the effects of explosives on structures, and, crucially, on models of structures, was transferred to the Road Research Laboratory, RRL (now TRL).
Barnes Wallis approached RRL in October 1940, to discuss the possibility of attacking enemy dams, including the Mohne Dam. A team was set up at RRL under Dr A R Collins.
In a document written by Davey in 1993, he recalls that in late 1940, William Glanville brought Barnes Wallis to the BRS site at Garston for a secret meeting where Wallis’ plans to attack the Mohne and Eder dams were outlined. At that meeting, it was decided that the most effective way to determine the weight of explosive needed, and optimum location to detonate it to breach the dam, was to construct and test a scale model. Davey agreed to build this at BRS, and work began in November 1940.
Dr Davey designed a 1/50th scale model of the dam, to be built across a small stream in secluded woodland at the edge of the BRS site.
The model, which survives today at the centre of the now enlarged BRE site, was built in seven weeks between November 1940 and January 1941. Temperature records from the time show that the winter was very cold, with daytime temperatures close to or below freezing over much of this period, and photographs show snow on the ground.
The model at BRE was subjected to explosive testing, carried out by staff from RRL. These tests were to determine the distance from the dam wall that gave the greatest effect. Ten charges were detonated, at distances of three feet, two feet and one foot from the dam, on the bottom of the pool. A test probe placed against the dry side of the dam measured the deflections that resulted. Photographs from the time show that after the sixth charge was detonated, sufficient damage was caused to make water leak through the dam, and part of the parapet had been blown away. By the time the tenth charge was fired, the model was badly damaged.
The first public mention of the 1941 testwork at BRE was in a news release from the Air Ministry in 1954. This started with the line ” ‘Dig-for-Victory’ allotment holders at Garston, near Watford, were bewildered and annoyed, early in 1941, when a mysterious and sudden onrush of water swept down a nearby hill and inundated their plots”
It went on to explain that “The flooding at the Hertfordshire allotments came from the breaching of the first detailed scale model of the Mohne Dam which was tested… at the Building Research Station”.
In reality, the dam was never breached, and it is very unlikely that a large amount of water rushed down the stream at any point. This news release was issued as the final shots for the film The Dambusters were being recorded, and means that the very first tests at BRE were not reported in the film.
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1:50 scale Mohne Dam. The History. Operation Chastise, or the Dambusters raid. Even before the declaration of World War II, ways were being considered to disable the vast hydro-electric power stations of the Ruhr valley that were known to power the munitions factories in the area. Amongst these was the idea by engineer and aviation […]