 As microwave systems entered service , along with updated versions of aircraft carrying them , the problem arose of what to do with those aircraft carrying Mk . IV that were otherwise serviceable . One possibility , suggested as early as 1942 , was homing in on the Luftwaffe 's own radar sets . The basic operational frequencies of the Luftwaffe 's counterpart to the Mk . IV , the FuG 202 Lichtenstein BC radar , had been discovered in December 1942 . On 3 April 1943 the Air Interception Committee ordered the TRE to begin considering the homing concept under the codename Serrate . As luck would have it , this proved to be perfect timing . In the late afternoon of 9 May 1943 , a crew from IV / <unk> defected to the UK by flying their fully equipped Ju <unk> @-@ 1 night fighter , D5 + EV , to RAF Dyce in Scotland , giving the TRE their first direct look at the Lichtenstein . 
