During the spring of 1958, Peter Wright of MI5 began an effort to track the radios of KGB agents in Britain called "Operation Rafter". Most radio receivers contain local oscillators which generate a radio frequency signal even when they are merely receiving. This is often referred to as 'radiation'. MI5 sought to locate clandestine receivers based on picking up this radiation using a sensitive receiver. One of the problems was interference from cars, domestic radios and televisions. Indeed, they were using a technique that was similar to that later employed by TV detector vans.
Initially, these activities were conducted from MI5 detector vans, but soon a more elaborate version was launched called "Airborne Rafter" using the sigint resources of the RAF. The initial aircraft used for "Airborne Rafter" in the late 1950s were Lincolns and Ansons, the former being drawn from the RAF's 151 Squadron at RAF Watton. By 1961 the mainstay was provided by two Vickers Varsities, serial numbers WF389 and WL679, which were nominally allocated to RAF Farborough. WL679 (pictured above in Farborough colours) was employed on a range of exotic radio warfare experiments down the years with Farnborough and Pershore. It was the last Varsity to serve in the RAF and is now on display at the RAF Museum at Cosford.
In 1961, the The CIA were dismayed to learn that this technique had been shared with the FBI and the Canadians, but not with them. In 1963, "Airborne Rafter" was shut down after review of sigint costs by Sir Stuart Hampshire, reflecting its lack of productivity and the rising cost of the flights.