British command during WWII is desperate to disrupt German production in the Ruhr Valley. Toward that end, they devise a clever and complicated plan to blow up crucial dams on the Ruhr River. Eccentric genius B. N. Wallis, played by Michael Redgrave, has devised a bomb that will bounce across the surface of the water and explode as it reaches the exact optimum depth. The only trouble is that the bomb must be dropped at a very precise height from a plane going a very precise speed at a very precise distance.
The first two-thirds of the movie explores the ingenious ways in which these problems are solved and the last third is the exciting mission itself. For those who liked The Man Who Never Was (1956), a movie about another British and American plan to mislead the Germans.