The AMES Type 7, also known as the Final GCI, was a ground-based radar system introduced during World War II by the Royal Air Force (RAF). The Type 7 was the first truly modern radar used by the Allies, providing a 360 degree view of the airspace around the station out to a distance of about 90 miles (140 km). It allowed fighter interceptions to be plotted directly from the radar display, a concept known as ground controlled intercept, or GCI.Earlier radars, like Chain Home (CH), provided the range and angle to a single target at a time. Arranging an intercept required a complex series of reports from multiple stations that were plotted at a central station. In a seminal 1939 memo, Robert Hanbury Brown showed that this Dowding system resulted in an inherent inaccuracy of approximately 5 miles (8.0 km), and the only way to reduce this would be to arrange the interception directly from the radar screen. He suggested spinning the radar antenna and the CRT display to produce a 360 degree picture of the airspace around the station, a concept he referred to as a plan position indicator, or PPI.
