70-years-ago today more than a hundred men flew on a mission that became known by their nickname - The Dambusters. 19 Lancaster bombers set out from RAF Scampton in Lincolnshire to attack a series of dams in Germany's industrial heartland with a newly-invented bouncing bomb.
Two of the main dams were badly damaged but despite that success eight of the aircraft were shot down and more than 50 crew killed. The bomb itself had been tested amid great secrecy in the New Forest in Hampshire and off the coast of Kent and Dorset.
In the first of three pieces, our Correspondent Derek Johnson takes a look at how this extraordinary device came into being and at the man whose genius dreamed it into being.
He speaks to Mary Stopes-Roe, the Daughter of Barnes Wallis and Bob Payne and Ant Larkins, who saw the bouncing bomb tests.