In 1886-1888, Heinrich Hertz, a German physicist, did some experiments and found that radio waves were reflected by metallic objects. This had suggested before in James Clerk Maxwell’s work on electromagnetism.

Hertz’s experiment was the start of RADAR (Radio Detection And Ranging) technology. But it was just in the early 20th century that the system becoming widely available. In 1904, a German inventor, Christian Hulsmeyer used the technology first to build a simple ship detection device to avoid collisions in fog. This system became the first early warning system for sailing. True radar system was developed over the next two decades.

On June 17, 1935, the new detection system was first demonstrated in Britain and it would later be called radar. Sir Robert Watson-Watt (1892-1973), a Scottish physicist, designed the first set into practical use. He conducted full scale tests of a fixed radar radio system that would be known as Chain Home. This early detection system detected an incoming bomber by radio signals.

At first Watson-Watt was asked to developed an instrument that can transmit a ray that could destroy German aircraft before they attacked but he thought that such a thing was not feasible. He believed however, that he could develop a machine able to detect an aircraft in flight.

Along with Wilkins and Bowen, Watson-Watt are generally credited as modern radar inventors. But several other investors have also developed this system after that and creating a radar as we know today.