 By late 1939 it was realized that the rotation of the beam on the radar display could be accomplished using electronics . In December 1939 , <unk> Dummer began development of such a system , and in June 1940 a modified CHL radar was motorized to continually spin in bearing , and connected to one of these new displays . The result was a 360 degree view of the airspace around the radar . Six copies of the prototype Ground Control Interception radars ( GCI ) were hand @-@ built at <unk> ( Air Ministry Experimental Station ) and RAE during November and December 1940 , and the first went operational at RAF <unk> on New Year 's Day 1941 , with the rest following by the end of the month . Prior to their introduction in December 1940 the interception rate was 0 @.@ 5 % ; by May 1941 , with a number of operational GCI stations and better familiarity , it was 7 % , with a kill rate of around 2 @.@ 5 % . 
