The radar invented by Robert Watson-Watt, was invaluable to the men who fought the Battle of Britain. The radar allowed Britain to track incoming German warplanes and gave Fighter Command, led by Sir Hugh Dowding, sufficient time to get airborne and attack them.
A chain of radar stations covered the south-east of England. The above photo shows a German attack on the Dover radar station in 1940. Combined with the work of the Royal Observer Corps, radar was the eyes of the RAF and Fighter Command in particular. The pilots of Fighter Command needed to be in the air as soon as was possible in an effort to stop the Luftwaffe getting to London. It was radar that gave them this time. It also allowed the pilots to stay in the air longer as the pilots could be given specific bearings as to where they could find incoming enemy planes - as opposed to time spent hunting for them and wasting valuable fuel reserves.
Robert Watson-Watt is given the credit for inventing the radar. The first experimentations into what we would define as radar came in 1888 when Heinrich Hertz discovered that radio waves could be bounced off objects. In 1904, Christian Hulsmeyer patented an early warning system for shipping. Therefore, Watson- Watt did have prior research to inspire him.
In 1935, Watson-Watt was asked to the Air Ministry to investigate the possibility of creating a 'death-ray' weapon using radio waves. At the time, Watson-Watt was working for the National Physical Laboratory in Slough. He did not invent a 'death-ray' weapon but he did find that his radio transmitters could create an echo from an plane that was over 200 miles away. Such a distance would give the RAF an early warning of an attack. As his work was done during the build-up to World War Two, such an invention was invaluable to the RAF that believed it was significantly weaker than the Luftwaffe. During the Battle of Britain, the Germans lost the element of surprise.