Radio Proving Flights

192 Sqn Lincoln Throughout the cold war RAF and other NATO countries routinely conducted flights along the borders of Warsaw Pact countries to gather electronic intelligence (COMINT or ELINT) – these activities were described as ‘Radio Proving Flights’. The purpose of these flight was to allow the intelligence community to build up a picture of the Soviet Air Defences, upon which RAF Bomber Command could then base their operational plans.

The RAF flights were initially undertaken by No 192 Sqn from RAF Watton using five specially equipped Lincoln B2 aircraft – these aircraft were later supplemented by four Washington RB-29’s. In August 1958 No 192 Sqn was re-numbered 51 Sqn. The flights all took place over friendly or neutral territory or over international waters – no penetration of Warsaw Pact airspace was involved. The main area of operations for the RAF during the 1950’s and 1960’s were the Barents Sea, the Baltic, the Black Sea and the Soviet/Iranian border. The Prime Minister was sent a copy of the proposed monthly programme of flights for his approval. Once Prime Ministerial approval was obtained for the overall monthly programme, Ministry of Defence and Foreign Office officials then carefully planned each individual flight and final authorisation rested with the Secretary of State for Defence.

The principle rules governing RAF ‘radio proving flights’ were:

  • Aircraft approached no closer than 30nm to Soviet or Satellite territory. (The Americans rules allowed aircraft to operate up to 20nm from the border, although in the Arctic this was extended to 40nm).
  • Except in the case of West Germany, aircraft were not permitted to overfly the territory or territorial waters of friendly or neutral countries whilst engaged in these operations without the concurrence of the competent authorities in the countries concerned.
  • No more than 4 aircraft were used together in the same operating area.
  • Daylight operations were limited to single aircraft.
  • Single aircraft operating by day or night were not permitted to make a direct ‘provocative’ approach to the coast or border and had to fly broadly parallel to the coast line.
  • Operations involving more than one aircraft had to be normally flown in conditions of total darkness and in any case under conditions of the light than ‘half moon’.

The American intelligence community also ran their own electronic intelligence gathering operations using, during the same period, the RB-47. The American government submitted a monthly list in advance to the British government detailing when an RB-57 intelligence gathering flight was planned to operate from a British base, such as Brize Norton. A copy of the RAF monthly programme was also forwarded to the American government. Radio Proving Flight Co-ordination Meetings also took place on a regular basis between British and American officials.

Comet R2

RAF flights were usually conducted with two aircraft, a Comet R Mk 2 and a specially equipped Canberra also from 51 Sqn. Typically, the Canberra would fly a profile that would attract the attention of the Warsaw Pact radar defences, allowing the Comet to record the transmissions. This would usually involve the Canberra flying at low-level below radar cover towards the target area and then, as the aircraft neared the miniumum distance they could approach the Warsaw Pact boundary, it would suddenly climb rapidly into radar cover alerting the air defence radars. Meanwhile the Comet would sit back at higher altitude, flying parallel to the boundary, listening in and recording the frequencies and transmissions of the radar and radios used by the air defence forces. Direction finding equipment on-board the Comet would also enable the location of the radar and transmitters to be determined.

Canberra of 51 Sqn

However, flights were conducted throughout in strict radio silence, to maintain an element of tactical freedom and surprise whilst concealing the identity of the aircraft from the Russian defences. Radio silence was only broken in an emergency or to recall the aircraft. As far as it can be ascertained, no RAF aircraft conducting a ‘radio proving flight’ was ever lost, although a number of American aircraft were shot down whilst engaged in these activities.


The last Comet R Mk2 of 51 Sqn was retired in 1975. Three Nimrod R1 aircraft gradually took over the electronic intelligence gathering role from the mid-1970’s operating from RAF Wyton. Today 51 Sqn is still operating with three re-equipped Nimrod R1 aircraft from RAF Waddington.