Replica of the Mohne Dam, in the grounds of the Building Research Establishment, Garston


Heritage Category:
Scheduled Monument
List Entry Number:
Date first listed:


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The building or site itself may lie within the boundary of more than one authority.

St. Albans (District Authority)
St. Stephen
National Grid Reference:
TL 12429 01586

Reasons for Designation

The replica of the Mohne Dam in the grounds of the Building Research Establishment at Garston is a unique survival; it is the only test dam to survive from a small number built for the dam destruction experiments at Garston and as such is not only of national but also international importance. It gives testimony to the exhaustive nature of the top secret experimental bombing trials prior to the Dambuster Raid on the Ruhr river dams in Germany. It also illustrates the multiplicity of tasks for which local construction companies as well as national scientific staff could be conscripted into during the course of World War II. The Dambuster Raid is a world famous event. The secret trials prior to the event are, however, not so well known and the Garston replica gives graphic testimony to this lesser known side of the story.


The monument includes a replica of the Mohne Dam, built to a scale of 1:50, located within woodland in the centre of the grounds of the Building Research Establishment at Garston.

The replica is some 14m long and 1m high with a maximum thickness of 0.6m at its base. The dam wall holds back a body of water forming a D-shaped pond with a maximum width of 15m; the stream feeding the dam overflows through the centre of the dam wall into a small drainage channel. The dam wall itself is constructed of over 600,000 miniature mortar cubes with a concrete core; this copies the construction technique used in the real Mohne dam which is made of massive granite blocks with puddled clay to seal the join at its foundations.

The replica dam was constructed in December 1940 following discussions on proposals to strike a number of dams along the River Ruhr in Germany. Dr William Glanville the Director of the Road Research Laboratory at Harmondsworth invited the eminent engineer Barnes Wallis to the Building Research Station to discuss the alternatives with the then Head of Engineering Dr Norman Davey. It was agreed that scale models would be built to determine the best method of attack. Constructed in strict secrecy, the Garston replica took a local workforce just seven weeks to build. Tests on the most effective means of destruction included the detonation of ten charges on the `wet' side of the dam at distances of between 1 and 3 feet. Other ideas included the dropping of charges with pressure fuses at the base of the dam and then initiating simultaneous detonation with a single large bomb.

The Garston replica was the first step in a series of extensive tests on the best means of destroying the Ruhr dams; other model dams (none of which survive) were built and tested by Dr Glanville's staff before final experiments on a real dam near Rhayader in the Welsh mountains. In the event Barnes Wallis devised his unique bouncing bomb as a means to breach the walls of the Ruhr dams. On the 16th May 1943 19 Avro Lancasters of 617 Squadron left RAF Scampton led by Wing Commander G P Gibson loaded with the bouncing bombs designed by Barnes Wallis. The raid was deemed a success as one bomb inflicted a gap some 20m high and 77m long on the Mohne dam; the Eder dam was also breached. Although the dams were repaired fairly quickly (the Mohne Dam took just four months), the action provided a huge boost to the morale of the Allied war effort and is consequently world famous as the `Dambuster Raid'.

MAP EXTRACT The site of the monument is shown on the attached map extract. It includes a 1 metre boundary around the archaeological features, considered to be essential for the monument's support and preservation.


The contents of this record have been generated from a legacy data system.

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This monument is scheduled under the Ancient Monuments and Archaeological Areas Act 1979 as amended as it appears to the Secretary of State to be of national importance. This entry is a copy, the original is held by the Department for Digital, Culture, Media and Sport.

End of official listing

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