World War II Ground-controlled interception

the restored operations room in underground bunker @ raf uxbridge showing map , plotters , raf station names , readiness status boards on wall behind. shown sector clock

in original dowding system of fighter control, information chain home coastal radar stations relayed phone number of operators on ground floor of filter room @ fighter command s headquarters @ raf bentley priory. here information radar combined reports royal observer corps , radio direction finding systems , merged produce single set of tracks , identified number. these tracks telephoned group headquarters responsible dealing target. group assign fighter squadrons tracks, , phone information section headquarters, in direct contact fighters. these fighter aircraft scrambled intercept aircraft.

because chain home radar stations faced out sea, once airborne intruders had crossed british coast no longer tracked radar; , accordingly interception direction centres relied on visual , aural sightings of observer corps continually updated information on location , heading of enemy aircraft formations. while arrangement worked acceptably during daylight raids of battle of britain, subsequent bombing attacks of blitz demonstrated such techniques wholly inadequate identifying , tracking aircraft @ night.

experiments in addressing problem started manually directed radars being used sort of radio-searchlight, proved difficult use in practice. attempt made using height finding radar turned on side in order scan arc in front of station. proved workable, , extended covering full 360 degrees making minor changes support , bearing systems. making display system, plan position indicator (ppi), displayed 360 degree pattern proved surprisingly easy, , test systems available late 1940.

starting in 1941 raf began deploying production models of gci radar, first expedient solutions, , permanent stations. unlike earlier system radar data forwarded telephone , plotted on map, gci radars combined of these functions single station. ppi in form of 2d top-down display showing both targets , intercepting night fighters. interceptions arranged directly display, without need forward information on telephone links or similar. not eased task of arranging interception, reduced required manpower well.

as system became operational success of raf night fighter force began shoot up. further aided introduction of bristol beaufighter , ai mk. iv radar became available in numbers @ same time. these 2 systems proved potent combination, , interception rates doubled every month january 1941 until luftwaffe campaign ended in may.

the germans quite slow follow in terms of ppi , did not order operational versions of jagdschloss radar until late in 1943, deliveries being relatively slow after that. many still under construction when war ended in 1945.