Operation Chastise – Task and Means
On March 21, 1943, a special Royal Air Force unit, the 617 Squadron, was formed and tasked with destroying dams in the Ruhr Valley. Led by Wing Commander Guy Gibson, bombers were to fly at night along a dangerous route that left them exposed to deadly antiaircraft fire in order to come within viable attack positions, then accurately deliver their ordnance to the targeted dams notwithstanding protective torpedo nets shielding the concrete structures. The result was Operation Chastise, a daring raid against the Edersee, Sorpe, and Mohne dams conducted on the night of May 16-17, 1943, by 617 Squadron.
For years, the British had explored the feasibility of destroying the Ruhr dams in case of war, and various proposals were examined, but none produced a plan that stood a reasonable chance of success. The problem was accuracy: theoretically, a big enough bomb, such as the 10-ton Earthquake Bomb that burrows deep underground before exploding, could destroy a dam by seismic waves if dropped from 40,000 feet. However, no bomber existed that could carry such a heavy bomb to the required height, then drop it close enough to the targeted dam.
A smaller bomb, provided it went off against a dam wall at a sufficient depth, would destroy the dam, but the dams were protected by underwater torpedo nets to prevent that. British scientist Barnes Wallis finally figured out a solution: bounce a bomb over the water’s surface and over the torpedo nets like a skipping stone until it struck the dam’s wall, at which point it would sink down the wall, and once at the requisite depth, explode. The surrounding water would concentrate the resulting blast against the dam, resulting in a breach.
In order to get the explosive to skip on the surface, then sink along the dam’s inner wall after striking it instead of bouncing back, Wallis devised a spinning drum filled with explosives. A bomber would approach the dam flying low above its reservoir, and at the proper height and distance from the target, release the explosive drum, which a motor had set to spinning counterclockwise. The bomber’s speed would propel the drum skipping over the water surface, bouncing over the underwater torpedo nets. Once it struck the dam, the drum’s counter-rotation would ensure that it hugged the dam’s wall while sinking. At the proper depth, hydraulic pistols would set it off, and basic physics would take care of the rest.