Radar

Radar stands for radio detection and ranging, detection system that uses radio waves to determine the distance, angle, and radial velocity of objects relative to the site.

It was developed over the years with input from many sources. 

Robert Watson Watt designed the first set put into practical use. He designed and installed a chain of radar stations along the East and South coast of England. That system helped defend the British in WWII.

Radio-based detection and ranging was first demonstrated in Britain was on 26th February 1935, Watson-Watt demonstrated his ideas at Daventry.

The Germans developed their own version ( started with experiments by Heinrich Hertz, later with inventor Christian Hülsmeyer)  .