In the early years of the Second World War, aeronautical engineer Barnes Wallis is struggling to develop a means of attacking Nazi Germany dams in the hope of crippling German heavy industry. Working for the Minister of Aircraft Production, as well as doing his own job at Vickers-Armstrongs, he works feverishly to make practical his theory of a bouncing bomb which would skip over the water to avoid protective torpedo nets. When it came into contact with the dam, it would sink before exploding, making it much more destructive. Wallis calculates that the aircraft will have to fly extremely low () to enable the bombs to skip over the water correctly, but when he takes his conclusions to the Ministry, he is told that lack of production capacity means they cannot go ahead with his proposals.