duncan kennedy reporting. today marks the 80th anniversary of the start of the battle of britain, when the raf defended the country against wave after wave of bombing raids from nazi germany. the young british pilots flew new fighter planes called spitfires and hurricanes, turning the aircraft into iconic symbols of resilience. but what's never been revealed is the role played by a schoolgirl from london in their success, as sophie raworth explains. newsreel: way up in the sky, there are messerschmitts, junkers, heinkels and dorniers, that are going to get the thrashing of their lives... july, 1940, and nazi germany is beginning the first of many bombing raids in what became known as the battle of britain. but the raf‘s pilots managed to fight off the luftwaffe and defend these shores in their spitfires and hurricanes.

it is the most famous plane from world war ii. it played a crucial role in the battle of britain. but what we didn't know until now was the role that a 13—year—old girl played in this design. this new generation of fighter plane had originally been designed with just four machine guns. but this man, captain fred hill, a scientific officer in the air ministry, became convinced that four guns would not be enough. each plane needed eight. he faced stiff opposition. most thought eight guns would be too many, impossible to fit onto the planes, but captain hill was convinced he was right, so he turned to an unlikely person for help — his 13—year—old daughter, hazel, a talented mathematician. together, around their kitchen table, they worked through the night on complex calculations to prove that eight guns firing at least

1,000 rounds a minute was essential for success. they talk about burning the midnight oil and coming into the office late after everybody‘s gone, to carry out further calculations and borrow some bits of equipment to carry out experiments, more or less off their own bat, working very long hours because they were really dedicated to these things. and of course, people taking their work home. hazel told her sons about her role when they were growing up. its just amazing that history hangs on so fine a thread. you know, if she got the calculations wrong or if she hadn't been asked to help, and the decision had not been made to go with eight guns, who knows what would have happened? this graph, presented to the air ministry in 193a, was the result of hazel‘s calculations. with eight guns firing, the fighters typically had just two seconds to hit their target, before pulling away. they had to get incredibly close to the enemy planes —

just 250 yards away — to stand a chance of shooting them down. hazel‘s calculations meant the government changed its mind. the battle of britain proved to be a turning point in the war. it was the bravery and success of the pilots which made victory possible, but without the support of many others, the battle may not have been won. what a great inspiration for young people today, young girls in particular, that can look upon someone like hazel, in the early 19305, making such an important contribution. 80 years after the battle of britain, hazel hill is finally getting the public recognition she deserved. sophie raworth, bbc news. that's it. now on bbc one, time for the news where you are. have a very good night.

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