Original cavity magnetron, 1940.
© Science Museum / Science & Society Picture Library
This was developed by John Turton Randall (1905-1984) and Harry Boot (1917-1983) at Birmingham University. Radars that could produce clear images of distant objects played a decisive part in World War II, and worked by bouncing powerful, ultra-short radio waves (microwaves) off their targets. The cavity magnetron was the first practical device for producing such waves. It is also the ancestor of the magnetron that is used to power every microwave oven.