Of all the air raids carried out during World War Two, none are as enduringly famous as the attack by Lancaster Bombers against the dams of Germany’s industrial heartland. Commemorated in literature and film throughout the decades, the mission – which was codenamed Operation ‘Chastise’ – has come to epitomise British ingenuity and courage throughout the war.
Before the Second World War, the British Air Ministry had identified the industrialised Ruhr Valley in western Germany, specifically its dams, as vital strategic bombing targets – a choke point in Germany’s production chain.
In addition to providing hydroelectric power and pure water for steel-making, the dams supplied drinking water as well as water for the canal transport system. Damage inflicted here would also impact greatly on the German armament industry, which at the time of the attack was gearing up for a large assault on the Soviet Red Army on the Eastern Front.
Calculations indicated that attacks with large bombs could be effective but required a degree of accuracy which RAF Bomber Command had been unable to attain when attacking a well defended target. A one-off surprise attack might succeed but the RAF lacked a weapon suitable for the task.
The Bouncing Bomb
Barnes Wallis, the manufacturing company Vickers Armstrong’s assistant chief designer, came up with an idea for a unique new weapon, popularly called ‘the bouncing bomb’ (codenamed ‘Upkeep’). It was a 9,000 pound cylindrical mine that was designed to bounce across the surface of the water until it hit a dam. It would then sink and a hydrostatic fuse would detonate the mine at a depth of 30 feet.
In order to operate effectively, Upkeep would have to have backspin imparted on it before it left the plane. This required specialist apparatus that was designed by Roy Chadwick and his team at Avro, the company that also manufactured the Lancaster bombers.
By 28 February 1943, Wallis had completed plans for Upkeep. Testing of the concept included blowing up a scale model dam at the Building Research Establishment in Watford, and then the breaching of the disused Nant-y-Gro dam in Wales in July.
A subsequent test suggested that a charge of 7,500 lb exploded 30 feet below water level would breach a full size dam. Crucially, this weight would be within the carrying capacity of an Avro Lancaster.
In late March 1943, a new squadron was formed to carry out the raid on the dams. Initially codenamed ‘Squadron X’, no. 617 Squadron was led by 24-year old Wing Commander Guy Gibson. With one month to go before the raid, and with only Gibson knowing the full details of the operation, the squadron began intensive training in low-level night flying and navigation. They were ready for ‘Operation Chastise’.
The three main targets were the Möhne, Eder and Sorpe dams. The Möhne dam was a curved ‘gravity’ dam and was 40 metres high and 650 metres long. There were tree-covered hills around the reservoir, but any attacking aircraft would be exposed on the immediate approach. The Eder dam was of similar construction but was an even more challenging target. Its winding reservoir was bordered by steep hills. The only way to approach would be from the north.
The Sorpe was a different type of dam and had a watertight concrete core 10 metres wide. At each end of its reservoir the land rose steeply, and there was also a church spire in the path of the attacking aircraft.
On the night of 16-17 May 1943, the audacious raid, using purpose-built “bouncing bombs”, successfully destroyed the Möhne and Edersee Dams. Successful detonation required great technical skill from the pilots; they needed to be dropped from a height of 60 feet, at a ground speed of 232 mph, in extremely challenging conditions.
Once the dams were breached, there was catastrophic flooding of the Ruhr valley and of villages in the Eder valley. As flood water surged down the valleys, factories and infrastructure were badly affected. Twelve war production factories were destroyed, and around 100 more were damaged, with thousands of acres of farmland ruined.
Whilst two of the three dams were successfully destroyed (only minor damage was done to the Sorpe Dam), the cost to 617 Squadron was significant. Of the 19 crews that had set out on the raid, 8 did not make it back. In total, 53 men were killed and three more were presumed dead, though it was later discovered that they had been taken prisoner and spent the rest of the war in POW camps.
Despite the casualties and the fact that the impact on industrial production was limited to some degree, the raid gave a significant morale boost to the people of Britain and became enshrined in popular consciousness.