The Allies needed to strike at the industrial heart of Germany. The Ruhr River Valley was a main artery for the Nazi war machine, keeping it alive in part by harnessing the power of the river through a series of dams. Take out those dams, the Allies wondered, and the blood would stop flowing?
But how to destroy massive dams? UK aeronautical engineer Barnes Wallis had an idea, bouncing bombs that would skip over river defenses, sink to the dam base and then explode, hopefully destroying the massive structure.
Wallis came up with the spinning cylinder bombs, essentially a depth charge designed for use against a land-based target. Resembling a barrel, the bomb was filled with 6,600 of high explosive and slung beneath the belly of a RAF Lancaster bomber.
Instead of dropping the bomb from a higher altitude, aiming for the dam and running the risk of missing your one shot, RAF crews devised an attack that worked in tandem with the design of the bomb.
The RAF Lancaster's would fly nap of the Earth towards the German dams and release their bouncing bombs on the resevoir side of the dam at about 500 yards. The barrel-like bomb, set into a back spin upon release, would then ricochet off the surface of the water at about 200 miles per hour. The friction with the water would cause deceleration that would lead to the bomb sinking to the bottom of the resevoir, ideally against the wall of the dam.
Like a depth charge, the 6,000 pounds of explosive filler would detonate as it reached a specified depth. The explosive would vaporize the filler, creating a dense packed explosion under the pressure of the surrounding water. The water surrounding the bubble would turn to steam and expand, then retract created by the explosive bubble pulse. The shock wave would also pulse outwards, adding to the potential damage.
In mid-May 1943 the RAF set its sights on the Mohne, Eder, Sopre and Ennepe river dams. Only two would be breached. Three barrel bombs would strike the Mohne, breaching it. The Eder dam took two direct hits, a third striking high rendering it ineffective, destroying it as well. The pair of other dams, Sorpe and Ennepe were hit with single bombs each, doing no damage.
However, as with any effort to bring a fist down on a enemy, there were human costs. Of the eight RAF Lancasters shot down during the raid, 53 crew members were killed. And as the dams were breached and released a combined 350 million tons of water, 1,294 people were killed down river. A number of those killed, somewhere between 600 and 750 depending on the source, were foreign POWs.
Next week we'll profile some of the most potent air dropped munitions to come from Wallis, the Earthquake Bombs.