BRE’s Möhne Dam Test Model

Sunday September 14, 2014

For many years I had wanted to visit the BRE’s Möhne Dam Test Model, at their site in Watford. This is because of a fascination with The Dambusters, which partly stems from the fact that a distant relative, of mine, was a Dambuster. His name was Sergeant Harry John Strange

Len and I arrived at the BRE site just before 10:00 and, after parking the car, joined a small group of people who had also come to see the model. We were given a quick introduction by Peter White, BRE Marketing and Communication Manager, before he led us passed some of the BRE test buildings and in to a wooded area, in the centre of the site. Here, our group, of about a dozen, listened intently as Peter began to explain why the test model was built, how it was built, and by whom, with the aid of some large ‘A’ boards, which had further information and photographs on them.

Mohne  Dam

When we reached the model itself, we were allowed to walk all around it and explore the local area. A muntjac deer peered through the trees, while a green woodpecker flitted through the branches, as I took photographs of the dam, from all angles. 

We then went up to see the Prince’s House. The Prince’s House was designed by HRH Prince Charles and can often be seen as the test house in BBCs Watchdog programme. 

The Prince’s House

We then wandered back down to the model, before looking at some of the BRE test houses, that range from the 1960s through to the ECO-friendly houses, of the 21st century.

 BRE test houses

On our way out of the site, I managed to get a photo of Bucknalls House. Bucknalls is a Victorian house, built in 1855 for Henry Creed, that stood at the centre of the 180 acre Bucknalls estate. Frank Thomas, the last owner of the house, made substantial extensions to the building, during 1878 and 1903. The estate itself was sold off in six lots, in 1924.

 Bucknalls House

There now follows a brief history of the Möhne Dam Test Model. Enjoy.

It all began back in 1938 when, even before World War II had begun, Dr Barnes Wallis came up with the idea of destroying the dams of the Ruhr valley with a ten-ton bomb, dropped from a height of 40,000 feet. The bomb would bury itself in the ground and cause a massive ‘earthquake’ that would destroy the dams. There were three problems with this scenario:

  1. No bomb of that size could be manufactured
  2. If it could be manufactured no aeroplane could carry it
  3. No current aeroplane could fly anywhere close to that height

Undeterred, Dr Wallis continued to work on a way to destroy the dams, working out the size, and type, of charge and its location in relation to the dam.

In October 1940 Dr Wallis was invited to a secret meeting with Norman Davey and William Glanville, where it was discussed that a scale test model should be built and tested, to see exactly what size charge would breach the dam.

This meeting was so secret that it is still impossible to find out where it actually took place; Either at the British Research Station BRS, now BRE, Watford, or at the Road Research Laboratory RRL, now TRL, Harmondsworth.

The actual Möhne Dam was opened in 1913 and its highly detailed schematics were easily obtainable, by the British Research Station, allowing the plans to be meticulously recalculated, so that a 1/50 scale model could be built. 

The Original Plans

On Monday November 25, 1940 work began on clearing and excavating the site. The stream was widened and deepened and channelled through a pipe, that would flow beneath the dam. On Friday 29, the concrete foundation was poured, with the towers being cast on the following Monday December 2. The side wings were then added.

 Under Construction – December 1940

The model took four men, Norman Davey, A J Newman, A B Stapleton & A Smith, just 7 weeks to complete and, considering that the British winter was particularly harsh, with temperatures close to, or below, freezing on some days, this was no mean feat. Roughly 2 million scaled bricks measuring 0.4 inches long x 0.3 inches wide and 0.2 inches deep (10.2 x 7.6 x 5.1mm) were used to build the model, along with poured concrete.

Despite the best efforts of the planners, the model is not entirely correct. One of the measurements was incorrectly scaled, when they converted it from metric to imperial.

The model was completed on January 15, 1941 and, six days later, the reservoir was filled with water. Explosive testing began the following day, January 22, 1941. The model was then subjected to ten explosive charges from distances of three feet, two feet and one foot. 

 Locations of the test charges

After the eighth detonation the model was damaged, which allowed water to seep through some cracks. After the tenth detonation the model was severely damaged. 

 The dam is cracked after the 8th detonation

These were the first, and only, tests to be conducted on the dam. All further tests were completed at RRL Harmondsworth, using cast concrete dams. These tests made it possible to work out that a 7,000 lb bomb, placed against the side of the Möhne Dam, would be enough to breach it.


The model was then left to the elements and remained secret, until 1954, when the Air Ministry issued a news release.

” ‘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. The flooding at the Hertfordshire allotments came from the breaching of the first detailed scale model of the Möhne Dam which was tested at the Building Research Station”.

 Air Ministry news release – 1954

The truth is that there was no breach of the dam, that would have resulted in water flooding out the allotments. As it turns out, the news release was issued as the final scenes of The Dambusters film were being shot, hence no mention of the British Research Station in the finished film.

At some point, possibly in the 1960s, the model was restored, and altered. The repairers took a piece of poetic licence when they decided to add a ‘breach’ in to the top of the dam.

All of the test models at Harmondsworth were destroyed by the testing. 

The Nant-y-gro dam, in Wales, was blown apart during large-scale tests.

The ship testing tanks, at NPL, were broken up, in 1996.

The BRE Möhne Dam test model, is the only piece of this amazing story to remain intact. 

 In 2002, the model was scheduled by English Heritage as a historic monument of ‘not just national but also international importance’.

For further and more detailed information, follow the links below.

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