Barnes Wallis, assistant chief designer for Armstrong Vickers, came up with the idea for a bouncing bomb that could be used to target strategic dams in 1942.
His idea formed the basis of the Dambusters raid that took place in May the following year, causing major damage to two out of the three targets selected.
"I had the idea of a missile which, if dropped on the water a considerable distance upstream of the dam, would reach the dam in a series of ricochets, and after impact against the dam, would sink in close contact with the upstream face of the masonry."
His idea was advanced by research from another researcher, A. R. Collins, who discovered that an underwater explosion would have greater effectiveness if it took place with the device directly in contact with the target.
This later informed one of the most significant design modifications for the bomb – the need to impart backspin on it so that it would (a) fall behind the path of the plane and ensure that the explosion would not impact the aircraft and (b) so that the backspin would ensure the device stuck to the surface of the dam wall.
Barnes Wallis developed his idea at first on a very small scale – with marbles in a bath then with increasingly large models.
The bomb itself (technically a mine) was at first codenamed 'Highball' and interested the navy as a potential weapon against enemy ships. However, it eventually became known as 'Upkeep' after it first got the go-ahead for further development from the Air Ministry on February 26, 1943 and then, on March 17, the final decision was made to form a new squadron to deliver the weapon.
Wallis had just eight weeks to get Upkeep ready.
This blog is dedicated to the memory of Flying Officer Donald Hopkinson, a bomb aimer with 617 Squadron, who was killed in action on May 17, 1943, age 22.