Wallis's theoretical work, including early tests involving catapulting marbles across his family's bathtub, led him to believe that a single bomb might destroy a dam. He designed a 5 ton cylindrical bomb, which, when released at low altitude with a certain forward rate of airspeed and a certain rate of backspin, would literally bounce across the surface of the water, hit the dam, and drive itself down to the base of the structure before exploding, thus maximizing its effectiveness/damage. His hypotheses proved correct when, on the night of 16–17 May 1943, newly formed No. 617 Squadron's Lancaster bombers destroyed the Möhne and Eder dams, causing widespread flooding of Germany's industrialized Ruhr area. Wallis's "Tallboy" (12,000 lb) and "Grand Slam" (22,000 lb) bombs were employed against targets such as the Tirpitz, the Bay of Biscay U-boat pens, and the German V-rocket sites. His talent for seeing a complex problem, formulating a solution, and bringing it to fruition proved invaluable to the Allied war effort. Despite receiving little recognition in his own time, Wallis continually advanced design engineering.
Knighted in 1968, Wallis did important and innovative design work after the war, including work on variable-geometry ("swing-wing") aircraft and supersonic aircraft. He died in Effingham, England, on 30 October 1979.
Matthew Alan McNiece
Brickhill, Paul. The Dam Busters. Rev. ed. London: Pan Books, 1983.; Morpurgo, J. E. Barnes Wallis: A Biography. London: Longman Group, 1972.