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A washtub, a catapult and some marbles

Most big stories have humble beginnings. Mary Stopes Roe, the daughter of Barnes Wallis, inventor of the bouncing bomb, talked in an exclusive interview with the RAF Benevolent Fund about her father setting up an experiment on the balcony of their house.

Mary says: "We had this wonderful experiment at our family home, where my father set up the washtub and got a catapult made by his department and he altered the angle of the slant that the ball was going to be delivered at and the distance from the water and then he bounced my sister's marbles, which she has never forgotten – the fact that they were her marbles.

"My brother had to check how far between the bounces of the marbles, whether they went over or under a string, the height of the bounce, but all we had to do was to find the marbles!"

She says this kind of playful approach was very characteristic of Wallis.

"He had a very playful side to him. Of course, the more the pressures of war built up, the less he was able to join in with things. But he played a great many games in the garden – we had a big croquet lawn and a lawn set out for coits and badminton."

Perhaps it was this same element of playfulness – at least to the mind of a pragmatic military man – that made Air Chief Marshal Sir Arthur Harris comment that it was ‘just about the maddest proposition of a weapon that we have come across’ and that the inventors of it should be ‘given one aeroplane and told to go away and play while we get on with the wars.’ He later changed his opinion.

This blog is dedicated to Flight Lieutenant Robert Barlow, a pilot with 617 Squadron on the Dambusters raid, who died age 32 after his plane crashed into overhead cables and crashed.

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