The eighteen girls of Course 82, undergoing intensive training in the theory and practice of radio direction finding, were constantly reminded that although they were allowed to let their hair down from time to time, their main task was to work hard and pass their exams.

If you failed you would be declared FT – which meant that further training was needed – or, the greatest ignominy of all, CT, meaning ‘cease training’, in which case you would be sent off to become a driver or a batwoman instead. There was another incentive to pass: on completing the training they would be given a whole week’s leave before being posted, which could be anywhere around the country.

At first, Kath feared that the other girls would all be cleverer than her. But the science was so far beyond anything taught in school that they were all, in effect, complete beginners, and she soon discovered that she could grasp the principles quite quickly. Even so, she was careful to revise each lesson at the end of the day to make sure she fully understood before they moved on to a new topic.

Only now was she beginning to appreciate the scale and ambition of the operation in which they were to play a small part, with its vast network of transmitting and receiving masts that linked all along the south coast of England, and up the east coast as far as Hull. She was awed by the thought of the legions of men and women working to track the movements and co-ordinating the responses of fleets of ships and squadrons of fighter and bomber planes in the seas and airspace between the British Isles and the continent.

Although the operators were mostly hidden away inside concrete bunkers in remote locations, watching signals on fuzzy screens and communicating their information down crackly telephone lines, Kath now felt very much ‘in the thick of it’. She began to understand properly, perhaps for the first time, some of the terrifying realities of war: how alone Britain was, with the Germans nipping at their heels from just across the Channel and thousands of men and women risking their lives each day to fight them off.

The more she learned, the greater her respect grew for the inventions of Vic and his fellow boffins. She never tired of watching the radar echo from an aircraft when it first appeared as a tiny blip in the noise on the cathode ray tube, and then grew slowly into a big deflection as the aircraft came nearer. This strange new ability to ‘see’ things at great distances, through clouds or darkness, seemed like a very special power – a magical extension of the usual human senses.

But this ‘special power’ also brought with it heavy responsibility. Failing to decipher the dots and squiggles on the tube correctly could cost lives; not only the lives of British airmen, but also those civilians whose homes and factories lay beneath the path of the German bombers.