Looking Down the Corridors

by Kevin Wright

  The Gabriel aircraft’s main mission was intercepting and analysing electromagnetic emissions from Warsaw Pact Air Forces in the GDR, Czechoslovakia and Poland. Their targets were radars, radio beacons, air-to-air and air-to-ground radio communications, data link transfer systems, etc. They noted frequencies, call signs and operational procedures. Radars of all types were located and their function determined and classified, including airborne radars and those of air-to-air missiles. It was essentially about ‘hoovering up’ as many transmissions as possible to establish the Soviet and Warsaw Pact EOB. After each Soviet conscript troop rotation, most radio frequencies, call signs and operators were changed, so out-of-date information had to be updated as quickly as possible. During these periods all the staff would be very busy and the Gabriel aircraft would often fly multiple missions daily, with additional aircraft on standby, until the EOB had been re-established and verified.

  Missions were generally carried out during daylight, but this routine would change during Warsaw Pact exercises, periods of unusual activity, or in times of crisis. A Gabriel that left Metz between 0900 and 1000 would arrive at Tegel and spend the night there. But timetables could vary depending on the briefed mission and other contingencies, so the aircraft might return to Metz on the same day. Mission reports would be sent to Metz via the Berlin-Tegel ground monitoring station.

  Gabriel missions from Metz followed three main routes:

  RE1: Inner German Border: The route ran from Metz to Frankfurt-am-Main and then to Würzburg adjacent to the Czech-GDR border. It then turned north to Lichenau, Leine, Hamburg and, finally, to Michaelsdorf, a tiny village close to the North German coast, before returning to Metz.

  RE2: Czechoslovakian border: This followed RE1 to Würzburg covering areas between the Czech-GDR border including passing close to, or over, Nuremberg and towns like Bayreuth, Allesburg and Straubing before returning to Metz.

  RE3: Berlin Corridor flights: From Metz the route headed towards the entrance of the selected Corridor – South, Central or North – then to Berlin, followed by a night stop at Berlin-Tegel before returning to Metz.19

  The latter mission profile was sometimes called a ‘Baltic’ when, after departing Berlin-Tegel, the aircraft would route through the North Corridor, head for Hamburg and then towards Malmö in Sweden. It would fly in international airspace, over the Baltic Sea, flying parallel to the edge of Polish and Soviet-controlled airspace. After leaving the Baltic area it would return to Berlin-Tegel after an approximately six-hour flight. Baltic missions were only flown during the winter because in hot weather the Noratlas had insufficient range to complete the mission. Flying close to the Swedish, Polish and Soviet borders regularly triggered a reaction from the Swedish air defence forces, which sent J-35 Draaken or J-37 Viggen fighters to intercept the ‘intruder’. The Soviets too regularly launched interceptors to have a closer look at the Gabriels and photograph them.

  Michel Adam, pilot and Commander of EÉ 54 between 1970 and 1972, describes the unit’s flights as being undertaken during the Soviet and East German forces’ ‘normal working hours’ and occasional night-flying periods. Flights along the IGB and Czechoslovak borders were flown at altitudes between 10,000 and 15,000ft, at a speed of around 160 knots, and lasted around six and a half hours. Flying at such altitudes meant that the Gabriels on Corridor missions were able to collect emissions well beyond the GDR into Poland.

  The NATO ADIZ along the IGB meant that there was little risk of accidental border penetration, but navigation needed special attention. Corridor missions required more careful flying and there was always heightened tension onboard. Flights were generally flown under Instrument Flight Rules (IFR) keeping to the Corridor centreline. The lack of pressurisation, the noise level in the cargo hold, and the inability to avoid bad weather often made flights challenging. In winter, icing added to the difficulties and in summer there were often strong stormy conditions – especially over the Bavarian mountains, whilst in the north there was often considerable air turbulence.20

  The Noratlas would remain outside the Inner German ADIZ that ran parallel to the GDR and Czechoslovakian borders. Because they flew close to the ADIZ the aircraft were sometimes intercepted by NATO fighters. When this happened the Gabriel crews would occasionally play games with them by gradually reducing their airspeed to see how long the escorting interceptor could stay with them until it either stalled or had to break away. Corridor flights were limited to the agreed maximum ceiling of 10,000ft, but more normally flown between 7,500 and 8,500ft and much lower when on occasional photographic tasks.

  Accurate navigation was of paramount importance in the Corridors and depended mainly on the radio navigator’s skill. For most of the flight, pilots flew the aircraft manually. The interception of messages from Soviet radars and fighter aircraft on the other side of the border would soon indicate that the Gabriel had been identified. The Gabriels were easily tracked by Soviet air defence radars, who named them ‘Lobsters’. They knew the difference between a standard Noratlas and a Gabriel variant. Fighters sent to provide visual identification would sometimes position themselves below and adjacent to the Gabriel to check for the presence of the two tell-tale ventral radomes and, if they were present, would report ‘it’s a male’.21 The Soviets regularly used the Gabriels as training targets for their fighter pilots and SAM operators, but this was a double-edged sword because by doing so they provided the French listening crews with a valuable source of information. Like their British and US counterparts, Gabriels were sometimes subjected to ‘meaconing’ that retransmitted false radio beacon signals on genuine frequencies to try to lure the aircraft outside the Corridor. The Gabriel’s onboard operators could determine, with a few minutes’ delay, their aircraft’s position as it was seen on the Soviet’s own radar scopes, using the intercepted signals passed between the radar sites and their command centre.

  EÉ 54 aircraft also worked in conjunction with MMFL ground tours. Having detected a ‘new’ emission from an unknown location, they would ask the MMFL to investigate the site, if possible, to visually confirm what was there. The absence of a robust French photographic capability meant that this was often the only way to verify visually the physical presence of equipment at a particular location.

  A Typical Corridor Comel Mission

  A few hours before a mission, the flight engineer, sometimes with a deputy, would thoroughly check the aircraft in the hangar, including activating all the electronic equipment to ensure it was functioning correctly. If all was well, the aircraft was available for flight barring any sudden aircraft, or engine, unserviceabilities. The flight crew and equipment operators would assemble in the briefing room together with the meteorologist, who would detail expected weather conditions. The GÉ’s night shift supervisor would advise of any incidents or events from the previous day’s flight that could affect the mission’s conduct. The BGÉ’s 2ème Bureau (intelligence) representative would brief the crew on new sightings, air and ground unit dispositions and any activity that might be important, or affect operations. The mission commander briefed the crew on the mission, its objectives, route, ETD, general safety and personal equipment.

  After briefing, the crew boarded the aircraft, with flight crew using the main cabin door and the ‘back-end’ team the rear door. Crew members would take their work station, preparing flight and personal equipment which usually included a parachute on Corridor flights. On reaching the assigned flight level, the ‘Team Leader’ ordered the turbine to be started so the operators could test their electronic equipment. The linguists would start working almost as soon as they passed over Frankfurt-am-Main, but the radar interceptors could only get to work as they entered the Corridor close to Mansbach when radar signals became sufficiently reliable.

  The Noratlas had no modern navigation aids, so the navigator would plot the aircraft’s course onto a map. The operators began looking for emissions based on the pre-briefed priorities. If a signal of interest was detected, it would be isol
ated and then subjected to an initial analysis that recorded essential details such as frequency and modulation. The precise identification of transmission locations became easier as signals became stronger. Once a target was fully identified the operators would move onto the next. Details of each intercept were passed to the ‘Team Leader’ who ensured the relevant information was transmitted back to base in summary form. If anything particularly new, or interesting, was revealed then the flight could be changed to try to capture it again on the return. After landing the aircraft commander would conduct a ‘hot debrief’ and all the COMINT and ELINT ‘take’ would be removed for further in-depth analysis and reporting up the chain of command.22 After the stop at Berlin-Tegel, often involving a night stay, the Gabriel would either depart to Metz or head north if a ‘Baltic’ was tasked.

  What would have happened if a Gabriel had been force-landed in the GDR? The French crews’ instructions were very similar to those for the British and American crews. All documents and maps were to be torn into small pieces and ejected from the aircraft using the marker flare ejector chute on the side of the aircraft. Once on the ground, the last man to leave the plane was to open the fuel drain taps inside the fuselage and discharge an emergency flare to set the aircraft ablaze.

  A Gabriel Photo Flight

  A regular transport Noratlas fitted with photographic equipment left Metz to fly the Southern Corridor, tasked to photograph a Soviet SAM site located on its southern edge.23 The Captain was one of the most skilled on the squadron, being EÉ 54’s Chief Pilot. The mission was flown, apparently without incident, and landed at Berlin-Tegel in the late morning as normal. The Commander of GÉT 30.351, Colonel Michel Danthon – a former Mirage III reconnaissance pilot and commander of 33 Escadre de Reconnaissance – received a phone call warning him that the Chief American Controller at the BASC was filing an ‘airspace violation’ against the aircraft for leaving the Corridor. His first reaction was ‘what difference does it make to the Americans?’ He believed that the Americans were probably concerned about the Soviet reaction to the alleged incident and so, to take the ‘heat’ out of the situation and pre-empt any Soviet indignation, decided to report it themselves. Danthon called the crew in Berlin and asked the pilot about the flight and the weather at the time. He was told that the flight was normal, weather excellent and there was nothing to report. The Soviets had still said nothing.

  At Metz the situation escalated and the Commander FATac called Danthon to tell him that the alleged incident had now reached diplomatic levels and the Quay d’Orsay was involved. Danthon was summoned to the Chief’s office to explain the situation. There was still no Soviet reaction. Before reporting to the General at FATac for an expected ‘one way chat show’, he consulted other unit members to try to find an alternative explanation for the alleged offence. At that time the Soviets were transmitting data from their radars in duplicate, via both microwave and HF radio. The French ground intercept stations had detected and recorded the Soviet radar information as the photo flight progressed along the Corridor. The unit’s analysts and linguists reconstructed the mission, seeing exactly the same picture that the Soviet controllers had seen – and plotted the results on a map. They saw the aircraft approach the edge of the Corridor to photograph the SAM site but never leave it. The French view became that ‘the Americans had, once again, over reacted’. Colonel Danthon reported the findings to his CO and was confident that there had been no violation. He delivered the details showing that the Soviet’s own radar information indicated that the aircraft never left the Corridor. As far as Danthon was concerned that was the end of the affair.

  When the Noratlas returned from Berlin the incident was discussed with the crew and it became very clear that the aircraft never left the Corridor’s lateral boundaries. However, in order to acquire larger-scale, higher-quality photography they had descended to around 2,500ft, which was below the Corridor’s lower limit. The American radar had detected this breach but the Soviet radar apparently had not, perhaps pointing to a potential limitation of Soviet radar capability that they did not want to expose.24 An alternative explanation might have been simply that the Soviets were well aware of the breach but chose not to make an issue of it on that occasion for reasons of their own.

  Listening to the Listeners

  On 10 March 1964, the French monitoring services had a front seat when they recorded the loss of a USAF RB-66B electronic reconnaissance aircraft from the 19 Tactical Reconnaissance Squadron (19 TRS) based at Toul-Rosières in France. USMLM’s 1964 Annual Report describes the flight as ‘local training flight’. The US account states that the aircraft was seen on radar approaching the Soviet Zone of Germany. The plane disappeared from the radar screen after it had reached the vicinity of Gardelegen in the GDR, north-east of Helmstedt.25 That official account gives little away about the real drama being played out. Doug Gordon’s description of the incident indicates that the aircraft was about 120 miles off course and well into GDR airspace. Four MiG-19s intercepted the aircraft and fatally damaged it with gunfire, forcing the crew to bail out.26 The rescued crew were treated for their injuries and handed back to the US military a few weeks later without further conditions, although it caused a diplomatic spat between the two nations. The USA has always stuck to the ‘navigational error’ story, whilst the Soviets insisted that it was a ‘provocation’ flight to test their air defences. Some accounts suggest that the aircraft was operating inside one of the Corridors but this is unlikely because of the ban on their use by ‘combat aircraft’ and the necessity to file a flight plan with the BASC prior to any Corridor flight.

  The French account of the incident offers a somewhat different perspective. It suggests that the RB-66 was operating near the entrance to the Central Corridor, where it was believed to be attempting to identify a new Soviet radar. The aircraft’s position was supported by the last radar trace being close to Gardelegen on the northern edge of the Centre Corridor and close to the Letzlinger Heide major training area. A Noratlas Gabriel V, flying in the Southern Corridor at the time, and the listening post at Berlin-Tegel recorded the RB-66 flying towards the IGB and then being downed by the MiGs. The intercepted radio conversations and exchanges were simultaneously translated and recorded by the Gabriel V and the ground station. Between them they were able to triangulate the position where the aircraft had come down.27

  The SA-10 Grumble Saga

  In 1977 a French Corridor mission intercepted Soviet radar emissions on new frequencies which stopped when the Gabriel aircraft approached their source. It was thought that these signals emanated from the new SA-10 Grumble (S-300) SAM system that had not been seen outside the Soviet Union at that time.

  To gather more information on this potentially important target, a ‘trap’ was organised using a photographic configured Noratlas cargo aircraft and a Gabriel operating in concert. The photo aircraft flew though the Central Corridor where the new SAM system’s signals had been detected in the area of the Letzlinger Heide training area, north-west of Magdeburg. The Gabriel flew along the Northern Corridor listening for transmissions. The Gabriel informed the photo Noratlas that the suspect emissions were being received. As the photo Noratlas overflew the training range, the emissions ceased but the aircraft activated its cameras anyway. The run of stereoscopic photographs revealed the radar vehicle in the process of retracting its antenna, which was an added bonus, and the Gabriel verified the system’s frequencies – a good day all round. The ‘trap’ produced the first aerial photography of the SA-10 Grumble system, which had hitherto only been operated under cloud cover to escape the prying view of American satellites.28

  Watching Us Watching You

  The co-ordination of ground stations’ activities with the Gabriels gave the French a unique capability. One ground station that collected HF transmissions, used an ingenious device that captured emissions from Soviet air defence systems. It consisted of an ‘automatic reader’ which intercepted the transmissions and then, using software i
nstalled on a PC, decoded the messages and displayed the track’s positions on a screen. This allowed the French to observe the position of ‘targets of interest’ to the Soviet air defence system at almost the same time as the Soviets themselves were looking at them. Denis Aubert describes the satisfaction it gave the French to view US Air Force SR-71 Blackbird flights operating far away over the Baltic Sea, using the Soviet radar picture to see them.29

  Fencer Arrives

  The first Soviet SU-24 Fencer fighter-bombers appeared in East Germany during late 1986 and early 1987, flying ‘racetrack’ patterns with another SU-24 pursuing and joining them. The communications interceptors picked up voice transmissions from the Fencers saying ‘contact’ and ‘separation’ as aircraft joined up and then broke away. The conclusion was that the aircraft were probably undertaking air-to-air refuelling (AAR) operations, but decodes of the Fencers’ IFF transmissions made it clear that no fuel transfer took place because the pilots were in the early stages of their AAR training. Later, the first live fuel transfer was recorded.30

  C-160 Transall Gabriel VI

  In 1984, the French Defence Department began searching for a modern SIGINT aircraft to replace the obsolescent Noratlas. A number of options were considered, with the C-160NG selected in March 1986 after multiple evaluations. Two standard C-160NG airframes, F-216 (G-1) and F-221 (G-2), were chosen for conversion to Gabriel VI configuration, both fresh from a recent overhaul and equipped with refuelling probes. Sogema was the prime contractor for the conversions, the key part of the new aircraft’s sensor suite being the Analyseur Superhétérodyne TACtique (ASTAC) ELINT system. This provided a quantum leap in reconnaissance capabilities over previous generations of equipment in the Noratlas. The C-160G Gabriel VI was distinguishable from a standard transport Transalls by the belly radome which contained the SPRUCE SIGINT equipment, two wingtip pods containing the ASTAC system and four antennae on top of the fuselage.