People today think that Barnes Wallis came up with the idea to destroy the dams of the Ruhr valley. This is not true; the Air Ministry had discussed the matter back in 1938, just in case Germany went back on the war path. The committee laid down clear objectives should the matter arise.
Map from the front page of The daily Telegraph 18th May 1943
1.Cut water supplies for industrial and domestic use.
2.Cause flooding and damage to industrial plants, rail tracks and water ways in the valley.
3.Prevent sufficient supplies of water for use in the inland waterway systems.
The dams that were under discussion were the Möhne, Eder, Sorpe and the alternative sites of the Ennepe, Lister, and Diemel dams. The Möhne being the most important of them, the reason being this dam near Dortmund was a catchment type dam its role was to collect rainwater and to prevent flooding of the valley. It also provided water for industrial and domestic use and in turn generated hydro-electricity for the Ruhr valley. The Eder was used to feed the important Mittelland Canal, prevent flooding and generating hydro-electricity, the others worked like the Möhne only smaller.
The idea was on the table but no one had any idea how to carry out such a task and so the idea was shelved.
The Möhne dam
Situated at Gunne and 25 miles east of Dortmund, construction of the dam was started in 1909 and finished in 1913. The wall was made of limestone rubble masonry and was protected against seepage by a clay bank to about one third of the water side face and with overflow outlets near the top. This construction stood 112 feet high and had a base thickness of 130 feet tapering to 25 feet at the top and is 2100 feet long. The dam holds back 135 million cubic metres of water, covering an area of 3229 acres. It was protected before the raid by 2 anti torpedo nets in the water and anti aircraft guns of 20 and 37mm calibre mounted on the shore and on each of the two towers.
After the raid over 2,000 workers took just 4 months to rebuild the wall ready for refilling. The power station at the base of the dam was washed away along with most of its foundations and was never re-built.
This was yet another very impressive dam being the largest masonry dam in Germany, it reached 138 feet into the air and was 119 feet thick at the base tapering to 20 feet at the top and a length of 1310 feet. The Eder is some 25 miles east of the Möhne dam. The Reservoir was much larger than the Möhne it could hold up to 7100 million cubic metres of water
This dam was built between 1927 – 1933, and was a completely different type of construction. It consisted of an earth work embankment and a concrete core. The wall height was only 58 feet but had the capacity to hold 72 million cubic metres of water. It is situated six miles south of the Möhne and even Barnes Wallis felt sure that his bomb would not work on this type of construction.
The Lister built between 1909 – 1911 with a wall height of 35 feet it was also of the masonry type “ideal for the bouncing bomb”, this dam had a capacity of 22 million cubic metres of water.