Radar is an acronym for Radio Detection And Ranging. It is a system which was developed during the Second World War to measure the distance and speed of objects using radio waves. It served as an early warning system, detecting distant enemy aircraft, which were otherwise undetectable with the naked eye.
A radar system can be used to detect an object's location and speed. The system works using a transmitter, a transmitting and receiving antenna (sometimes these are two separate antennae, but often only one will be used for both roles), and a processor. First, a pulse of electromagnetic radiation, normally radio or microwaves, is sent from the radar system. If the pulse reaches a solid object it will reflect off the object. This reflected wave is then detected by the receiving antenna and processed giving the user information about the object's location and speed.
Heinrich Hertz found that radio waves could be reflected off solid objects in 1886 and German physicist Christian Hülsmeyer was the first person to develop a system that could use radio waves to detect solid objects. In 1934 at the start of the Second World War, there were rumors that the Germans were creating a death ray. Robert Alexander Watson-Watt was asked to investigate the feasibility of such an idea. He calculated it would be impossible to create ray that could destroy anything, but it prompted him to think about other uses for radio waves. He created the first workable detection system using radio waves in 1935.
This system was rolled out all along the British coast, allowing the British military to have early warning of any incoming enemy bombers. Watson-Watts achievements are believed to have changed the outcome of the Second World War for the allied side. Watson-Watt was knighted in 1942 and given the US Medal of Merit in 1946 for his work on radar. The term radar was coined by the US Navy in 1939. Radar systems are now used all over the world for a number of civilian and military uses.