Operation Chastise was an attack on German dams carried out on 16–17 May 1943 by Royal Air Force No. 617 Squadron, subsequently known as the “Dambusters”, using a specially developed “bouncing bomb” invented and developed by Barnes Wallis. The Möhne and Eder Dams were breached, causing catastrophic flooding of the Ruhr valley and of villages in the Eder valley, while the Sorpe dam sustained only minor damage.
The two direct mine hits on the Mohne dam resulted in a breach around 250 feet (76 meters) wide and 292 feet (89 meters) deep. The destroyed dam poured around 330 million tons of water (equivalent to a cube 687 meters on each side) into the western Ruhr region. A torrent of water around 32.5 feet (10 meters) high and travelling at around 15 mph (24 km/h) swept through the valleys of the Mohne and Ruhr rivers.
A few underground mines were flooded; 11 small factories and 92 houses were destroyed and 114 factories and 971 houses were damaged. The floods washed away about 25 roads, railways and bridges as the flood waters spread for around 50 miles (80 km) from the source. Estimates show that before 15 May 1943 water production on the Ruhr was 1 million tonnes, this dropped to a quarter of that level after the raid.
The Eder drains towards the east into the Fulda which runs into the Weser to the North Sea. The main purpose of the Eder dam was then, as it is now, to act as a reservoir to keep the Weser and the Mittell and kanal navigable during the summer months. The wave from the breach was not strong enough to result in significant damage by the time it hit Kassel (approx. 35 km downstream).
The loss of hydro-electric power from the dams was the greatest impact on the Ruhr armaments production. Two powerplants (producing 5,100 kilowatts) associated with the dam were destroyed and seven others were damaged.
Perhaps the greatest value of the bombing can best be seen as a very real morale booster. The pictures of the broken dams proved to be a propaganda and morale boost to the Allies, especially to the British, still suffering under German bombing.