It all began 50 years ago in a muddy field in Northamptonshire with three scientists, an RAF bomber and a borrowed BBC short-wave transmitter. The experiment was to lead to the radar which won the Battle of Britain and defeated the U-boats in the Atlantic. Today civil airlines could not operate without it, neither could the space programme. Radar also forms NATO's first line of defence in the cold war; it has come a long way from that muddy field.