Radar is an instrument that uses microwaves to detect distant objects by measuring the echo of pulses. During World War II, countries rushed to develop radar systems for military use. Britain was a leader in radar development before the war and built radar stations around the country to detect incoming aircraft. There were two main types of radar used in WWII - detection radars to map surrounding areas and detect objects, and fire control radars to precisely locate targets to allow guns to hit targets that couldn't be seen directly. Early radar displays were like electronics lab equipment, but the PPI display, showing a rotating beam and target locations, became more useful for operators. Radar has since been developed for navigation and now has applications beyond military and weather