7. Overcoming the Technical Problems of Breaching a Dam
Initial thinking when it came to blowing up a dam centered on the use of a really big bomb – the bigger, the better. 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. Eventually, 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.
To get the explosive to skip on the water’s 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’s 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.