Green Archer ( radar ) Green Archer , also called Radar , Field Artillery , No 8 was a widely used British mortar locating radar operating in the X band using a Foster scanner . Developed by EMI after an experimental model by the Royal Radar Establishment , it was in British service from 1962 until 1975 with the Royal Artillery . A self - propelled version was designated FV436 or Radar , FA , No 8 Mk 2 . Mortars , using indirect fire , became a major threat to infantry in World War 2 . It was found that mortar bombs in flight could be detected and tracked by radar . US and UK anti - aircraft radars were used and specialised mortar locating radars appeared at the end of the war , and were used in Korea with varying degrees of success . Hostile mortars had to be accurately located before they could be attacked with indirect fire from guns or mortars . Since hostile mortars moved frequently to avoid return fire it was essential to have a means of locating them to a few tens of metres of accuracy and to be able to respond quickly when they are located . Green Archer provided a means of locating mortars quickly and accurately . Description . Green Archer comprised two units each mounted on a four wheel trailer with levelling jacks , one unit was the complete radar , the other a fully silenced generator inaudible at 200 m to permit operation in forward areas . The radar unit weighed 2 , 915 kg and with the antenna in the operating position was 2 . 9 m high . The radar display was positioned up to about 15 metres from the radar and had a built in simulator for training . Each radar and generator was usually towed by a Humber 1 ton armoured vehicle . Before Green Archer mortar locating radars had to track ( often manually ) a mortar bomb in flight for several seconds , having first " found " the bomb in flight . Finding was made a bit easier if the beam cone had a large angle , the problem with this was that it reduced the accuracy of location . Green Archer took a totally different approach . Green Archer ’ s distinguishing characteristic was its Foster scanner . This converted the narrow conic radar beam into one some 40° wide in azimuth and less than 1° high in elevation . The antenna was mechanically switched between two fixed elevations . The radar detected a mortar bomb as it passed through the lower beam , the operator marked it on his display and flicked the beam into the upper elevation , and again marked the bomb as it went through the beam . He then placed cursors over his marks and input the plot to the radar ’ s analogue computer . These two plots , the time between them and the angle between the two beam positions gave two points on a parabolic curve . Such a curve is defined by two points and is a good approximation of a mortar bomb trajectory . Using these , the azimuth of the radar beam centre and the radar ’ s coordinates , the mortar position coordinates were calculated . These could be adjusted to reflect the actual height of the ground . Green Archer could locate a medium mortar up to about 10 km away and a heavy mortar out to 17 km , the maximumrange . It took about 30 seconds from a mortar firing to producing its location . The radar could also be used " in reverse " to observe and adjust mortar fall of shot and that of guns firing in high angle . It was also capable of surface observation . In British service it was mostly organised as a radar section of two radars in the locating ( G ) troop of field regiments . In addition to the radars the section also had a command post and deployed two Listening Posts ( LPs ) . The task of the LPs was to report mortars firing and the area they were in . This told the radar to switch - on , and so avoided continuous transmission as an electronic counter measure . The other section of the troop provided an artillery intelligence section at brigade headquarters responsible for fighting the brigade ’ s counter - mortar battle . British Green Archers were successfully used on operations in Borneo , South Arabia and Oman against mortars and for border surveillance in Hong Kong . Each radar section was supported by an electronic repair vehicle which carried a spare for each of the 13 major sub - assemblies in each radar . Variants . A self - propelled version was fully developed . It was mounted on the cutaway rear of FV432 APC and designated FV436 or Radar , FA , No 8 Mk 2 . It had an automatic radar levelling arrangement using mercury , which was adopted for the Radar , FA No 15 Mk 2 , or Cymbeline that replaced Green Archer . However , it did not enter UK service . Nevertheless the cutaway hull design was applied to M113 APCs and used by at least three armies . Other Users . In addition to UK , Green Archer was used by : Germany , Netherlands and Denmark ( all SP on M113 ) , Italy , Israel , South Africa , Sweden , Switzerland . Survivors . A complete system , a radar trailer and a generator trailer , is preserved at the Radar Museum at RAF Neatishead in Norfolk .