Air of Authority - A History of RAF Organisation
Mobile OBOE after D-Day
The following is an extract from the AHB Monograph 'Signals Volume II, Aircraft Radio' produced in 1956. (Crown Copyright expired)
Deployment of Oboe Ground Stations on the Continent
Oboe facilities in the United Kingdom had proved to be adequate for the opening phase of Operation Overlord but it was, however desirable to implement Oboe coverage at the earliest possible opportunity by taking advantage of Continental sites. Unfortunately, all the available mobile equipment was deployed at home bases to provide the earlier and urgently required cover. Technical difficulties arose in connection with the equipment and the first convoys did not cross to the Continent until the third week in August. While the assault phase of the operations was in progress, the future of all radar ground stations which were to operate in the campaign was under review, and, on 15 May 1944, Headquarters No. 72 Wing was formed within the No 60 Group organisation to take over the responsibility for radar cover in the base area from mobile units of the AEAF thereby releasing those units for frontline support. Eventually the wing was made responsible for the maintenance of all radar navigation ground stations in the operational theatre, amongst which was included six Type 9000 Mark IIM convoys. Control of the ground reporting system was vested solely in groups of the AEAF. Headquarters No., 60 Group retained control of major, policy and of all details of a technical or operational nature, but day-to-day administrative control of the wing and its associated units on the Continent was maintained by the regional group of the AEAF.
The early work of the wing was mainly exploratory, most attention be, given to the preparations for its eventual deployment overseas. A small equipment section was formed at RAF Cardington on 15 May 1944 to act as a marshalling point for the equipping of convoys before they were called forward into the concentration areas. Meanwhile the first Oboe Mark IIM convoy was being at deployed at Bawdsey preparatory to overseas working. This convoy designated AMES No 9432, moved to Cardington on 9 August 1944 to await calling forward and its place at Bawdsey was taken by a second Mark IIM convoy, AMES No 9441. Some ten day's previously a forward element of Headquarters No 72 Wing, together with AMES Nos 7921 and 116. had left England, arriving at Anneville-en-Saire on the Cherbourg peninsula on 31 July 1944. There it remained until 30 August 1944 when it advanced to Chateau Mathieu, some five miles north of Caen.
Initial plans for the, extension of Oboe coverage over the Continent envisaged the establishment of two stations with two channels available at each, which would pair up with two corresponding stations in the United Kingdom. The Oboe technique required continuous voice contact between the controllers and the Cat and the Mouse stations during operations, which placed a heavy requirement on cross-channel communications; neither SHAEF nor Headquarters AEAF were able to provide the facilities from the small amount of circuits which existed at that time. By 23 August 1944, owing to the difficulty of maintaining landline communications across the English Channel, radio equipment and frequencies were provided and enabled a network to be set up for the control of Oboe missions. The efficiency of the system using radio channels was however, much lower than that of the same system using landlines.
On. 22 August 1944, the first Oboe Mark IIM convoy, AMES No 9432, landed on the Normandy beachhead. This unit, the third mobile radar ground station to be deployed on the Continent, proceeded direct to a pre-selected site on Mount Pincon. However, owing to an alteration in plans necessitated by the rapid advance of the Allied armies, the convoy was instructed not to set up station but to proceed to the Paris area. On arrival at the new site, Les Alluets du Roi the convoy began to prepare for action but this site was still too far in the rear for useful operations. Instructions were issued for the unit to prepare for an impending move into Belgium, and eventually the convoy arrived at Rosee, near Florennes, an 10 September 1944, when the station was set up, and operations, in conjunction with Hawkshill Down began on 15 September 1944. By coincidence the first mobile Oboe convoy to operate on the Continent was sited at the place against which one of the very first Oboe raids had been carried out, the calibration raid on Florennes on the night of 3 December 1942.
On 26 August 1944 an Air Ministry plan for the deployment of the first continental Oboe pair was formulated allowing for a two-channel station at Florennes in Belgium and a two channel station at Commercy in France. AMES No 9441, which had been undergoing field trials at Bawdsey, was called forward, arrived on. the Continent on 9 September 1944, and at Commercy on 14 September 1944. On the night of 25/26 September 1944, the first Oboe operation using the two stations was carried out. Six Oboe aircraft were despatched and all failed. The failure was caused by a breakdown in wireless transmission at one of the stations rendering all control impossible as the two convoys were out of touch with each other. After W/T contact had been established a heavy explosion shook the convoy breaking a valve in the rectifier circuit which could not be repaired in time to complete the operation. Oboe did not, therefore, get of to a flying start on the Continent and the difficulties were manifold. Snipers operated in the woods between the two convoys, mines were located in the vicinity, and much work was still needed on the communication side.
The initial disappointments were, however, soon overcome, and the use of Oboe was continued, until the cessation of hostilities, in aircraft of No, S Group and in the pathfinder squadron of the Ninth Bomber Division (M), Ninth Air Force. In October 1944 a preliminary survey of a heavy increase in Oboe failures experienced after D-Day, showed that they were in the main due to navigation errors resulting in aircraft, when called, being many miles away from the point at which they should have begun the Oboe run. The errors were undoubtedly due to the absence of Baillie beam installations, and inadequate Gee cover. The Rheims Gee Chain, and the provision of radio track guides, later did much to overcome the difficulty, and an increase in the number of mobile signals units and frequencies assisted in removing the other obstacles.
As the ground forces advanced on the Continent so tactical targets passed out of range of the Oboe Mark I stations at Sennen, Treen and Worth Matravers. The last operation on which Worth Matravers, the most easterly of the stations, was used, took place on 28 September 1944 and all the stations in the Southern Chain were closed on the night of 6 November 1944, when dismantling instructions were issued. The Mark I stations at Trimingham and Swingate had ceased to participate in any operational sorties in April 1944, but they were maintained in use for training purposes until the middle of January 1945. Of the remaining two pairs of Mark I stations, Hawkshill Down I and Trimingham I ceased operations on 20 November 1944, and Hawkshill III and Winterton II on 14 January 1945. Thereafter all Oboe operations were carried out with either the Mark II or the Mark III centimetre equipment. Gradually, the operations controlled by the mobile units based on the Continent reached their peak as those controlled by the home stations diminished until even the most easterly Mark II and III stations in the East Coast Chain were no longer required operationally. On 29 April and 8 May 1945 Oboe aircraft using Mark II and III channels at Winterton and Hawkshill Down marked pinpoints in Holland to enable Bomber Command aircraft to drop food to the Dutch people. These, however, were to be the last operational Oboe missions controlled by stations in the United Kingdom and all the Mark II and III channels at Winterton and Hawkshill Down finally closed down on 8 May 1945.
As the need for cover from the United Kingdom diminished so the requirement for additional Continental cover increased and at the beginning of September 1944 the four Oboe Mark IIM and the two Mark IISM units positioned at Beachy Head and Tilly Whim were also withdrawn for despatch overseas. Simultaneously, the siting of radar stations to extend radar navigation and precision bombing cover from continental bases became the first priority commitment of Headquarters No. 72 Wing, and the rapid changes in the military situation entailed a programme providing great resilience. Although the rapid deployment of units in forward areas provided no difficulty, operational delays were frequent owing to the unfeasibility of obtaining ground surveys rapidly. Conferences to solve these difficulties were held at Headquarters 2nd TAF, and a system of aerial survey was adopted which was accepted subject to confirmation by ground survey. It was subsequently found that where aerial survey had been attempted the two surveys were in close agreement. A build-up of Oboe stations on the Continent then began, and by the end of November 1944 ten two-channel convoys had arrived in France; of these, eight were Mark IIM convoys, and two Mark IISM. Four sites had been chosen, and the convoys were deployed so that there were two complete two-channel Mark IIM units on each site with three operational and one standby channels. The Mk IISM channels were split, one channel being deployed on each Type 9000 site. Meanwhile the transfer of Headquarters N o 72 Wing had been completed; the first main headquarters established at Chateau Mathieu was moved to Caen at the beginning of September 1944, and forward to Mons at the end of the month. Here it was joined by the remainder of the wing headquarters on arrival from the United Kingdom on 11 October 1944. At the same time the assistance of No 14 Air Formation Signals was made available to the wing for the establishment of landline and DRLS services: assistance of great value to a system such as Oboe, effectiveness of which depended largely on an extensive operational communications network.
Early in; December 1944 considerable reorganisation of the Type 9000 units became necessary in order to provide a complete four-channel convoy for deployment in the Strasbourg area, south of the existing mobile stations. In order to form this unit one Mark IIM channel was drawn from each of the Type 9000 sites at Florennes, Commercy, Laroche and Rips, together with one mobile workshop from both Florennes and Rips, and one controller's vehicle from Florennes. This convoy was assembled at Headquarters 72 Wing by 12 December 1944: on 14 December it left for the preselected site at Molsheim in France and become operational by 27 December 1944. The remaining Type 9000 sites were then left with three Mark IIM and one Mark IISM channels. The reorganisation of the convoys continued into 1945 and on 24 January 1945 all units as previously constituted were theoretically dissolved. Their convoy numbers were dropped and their personnel were posted to No 72 Wing Type 9000 Section where they were reassigned to units which were then designated Nos. I to 5 Type 9000 convoys. Individual vehicles were simultaneously allotted Cabin numbers. To maintain convoys efficiently in an area recently occupied by an enemy involves difficulties. The main problem was that of accommodation, it was difficult, to find winter quarters, large enough to accommodate complete crews, which were near enough to the technical sites to make communications easy and rapid, and, at the same time, economical in transport services. In some instances accommodation was available but was too widely dispersed. Nevertheless, the extension of Oboe coverage during this time enabled targets such as Stuttgart. Frankfurt, Schweinfurt, Ulm and Nuremburg to be brought within Oboe range.
In the middle of December 1944 a counterattack against the hitherto steadily progressing Allied offensive was staged by the enemy with the obvious intention of breaking through to the coast. Despite earlier plans, aimed at affording Maximum operational cover, which had been made with a view to the possible evacuation of forward areas in the event of such an attack taking place, the situation rapidly became critical, and for the first time the, ability of No 72 Wing to maintain cover in the face of rapid territorial changes was tested. Seven radar navigation ground stations in the Laroche area were endangered, including three Oboe Units, Nos. 9442. 9412 and 9431. As the enemy assault gained momentum two aspects of the situation increased in significance. In the first place was the need for maintaining units in an operational capacity as long as possible to assist operations of the Allied air forces and to enable plans to be completed for replacement sites to the rear. Secondly, it was vital to ensure that technical equipment of either a useful or secret nature did not fall into the hands of the enemy. By 16 December 1944 pressure had increased to such an extent that the Laroche area was swiftly becoming untenable and on 18 December evacuation instructions were issued detailing all radar navigation units to move to Florennes without delay. The withdrawal began shortly after midday and in spite of extremely bad road conditions resulting from a hard frost after a heavy, fall of snow, coupled with the intense amount of military traffic, was successfully carried out. There were no casua1tes to wing personnel and nothing of a secret or documentary nature was left behind for the enemy. Only a few of more than 100 vehicles were lost, and they were set on fire by American demolition units at the last moment. Resiting measures were immediately introduced but some delay in perfecting cover arose as the depth of penetration seemed likely to involve the Florennes area, necessitating further evacuation. Reserve, sites were chosen at Elincourt and the three Type 9000 units involved in the withdrawal returned to Headquarters No, 72 Wing for refitting. Although the evacuation of Florennes did not take place, the first of the three Type 9000 units, AMES No. 9442, to recommence operations did so from Elincourt on 4 January 1945, and radar navigation and precision bombing cover was re-established with the minimum delay.
In the new year the Molsheim area was also threatened by the enemy thrust beyond Strasbourg and on 2 January 1945 the area commander signalled to Headquarters No 72 Wing that a withdrawal was in progress and preparations to move had been instituted. The Officer Commanding No 72 Wing immediately gave authority for evacuation to be undertaken in emergency on the initiative of the area commander without further reference to wing headquarters. No risks were to be taken and all units were to withdraw to Commercy and await further orders. The order of retreat was specified, giving priority of movement to No 1 Type 9000 convoy and its associated mobile signals unit. By 4 January the position had become no longer defensible and the withdrawal to Commercy began. Again weather conditions were to cause long delays but all equipment successfully arrived at its destination.
Mid-January saw the end of the German advance and the re-occupation of both the Laroche and Molsheim areas came under consideration. Although Laroche was clear of the enemy a vast number of mines had been sown in the area and all habitable accommodation destroyed during the short-lived German occupation. Weather conditions were severe and heavy falls of snow had made movement difficult, but by 26 January 1945 the radar navigation units were again on their way back. AMES No 120 had already moved on 18 January to prepare the way for the arrival of the other units. No 2 Type 9000 convoy was the third unit to return to the environs of Laroche, arriving on 29 January 1945 at the site already prepared for it by AMES No. 120 and AMES No 7922, and becoming fully operational again on 5 February 1945. Meanwhile, plans to reoccupy the Molsheim area were under way, and on 18 January No 1 Type 9000 convoy moved to a site near Baccarat to await clearance of its former site. On 5 February the convoy returned to Molsheim and on 12 February it again became operational. The withdrawal from the sites and their reoccupation, drove home many lessons, notable amongst which was that the lighter mobile Gee-H equipment was better suited than heavy equipment for occupying forward emplacements where it could be left on site for a longer period provided the necessary mobile defence force: of light armour and anti-tank weapons were available. The experience gained influenced the deployment of all RNA units during the remaining months of the war in Europe.
By February 1945 the geographical structure of No 72 Wing had been re-established as it was in December 1944, but of necessity time was required for recovery after the Ardennes offensive. Nevertheless the Oboe stations were continuously used by aircraft of both Bomber Command and the United States Army Air Forces and the number of aircraft operating with the system against tactical targets was increasing daily. A special technique known as close-support attack, was adopted for sorties against vital targets close to the front line. On some occasions the targets were less than 1,000 yards in advance of forward troops and a high degree of accuracy was of major importance. Meanwhi1e a new method of assisting the navigation of Oboe aircraft. a rotatable radio track guide had been installed at Juvincourt. This had first been employed experimentally with Oboe aircraft in January 1945 and had proved of considerable value despite the severe limitation imposed by its remoteness from the front line. The promising results obtained with the equipment led to an expansion of the system and track guide were provided in the neighbourhood of the three Oboe units at Laroche, Rips and Commercy. The arc of rotation varied between 000 degrees to 170 degrees for Laroche. 010 degrees to 170 degrees for Rips, and 010 degrees to 160 degrees for Commercy. The frequencies allotted were 34.0 megacycles per second for Laroche and 34.4 megacycles per second for both Rips and Commercy.
The enemy was concentrating efforts on jamming Allied radar navigation and blind bombing systems. At the beginning of January 1945 severe interference was encountered on the Gee system but only a few sporadic attempts at jamming the Oboe centimetre wavelengths were reported. Jamming of Oboe began in earnest, however, in the early part of February, mainly during United States Ninth Air Force daylight bombing operations. First indications were the appearance of unlocked pulses having a fairly high recurrence rate. They overloaded the aircraft transmitter and resulted in poor repetition of the interrogating pulses, causing 'garbled' signals. Three main types of jamming followed, but as' the ground equipment was in all instances triggered by pulses received in an aircraft and retransmitted by it, no signals were received directly at the ground stations. The normal response seen on the ground station cathode ray tube was followed by one or more evenly spaced responses as the jammer and the aircraft transmitted back and forwards to each other. Little adverse effect on operations resulted. At first it was difficult to determine whether the interference was caused by the enemy or by radiations of radar systems on adjacent frequencies, but a survey undertaken in March 1945 established it as deliberate jamming. Subsequently a technique for locating jammers was independently conceived by both Nos 2 and 4 Type 9000 convoys and by a comparison of the logs of two stations carrying out an operation the approximate position of jammer was determined. A jammer near Mainz was excellently pinpointed in this way, but by the time the position was determined the Allied ground forces were over-running the area. Later, evidence was obtained of the location of jammers in the Ruhr area, and interference continued to be trouble-some until the latter half of April 1945, when presumably the speed of the Allied advance caused a complete disorganisation of the enemy efforts. Documents captured from the Luftwaffe after the surrender substantiated earlier intelligence reports that the enemy maintained an extensive organisation near the Ruhr valley whose sole function was the Jamming of Oboe or, as it was known to the Germans, 'Bumerang' it also transpired that the enemy had gained considerable advance warning of Oboe sorties by monitoring the Oboe high frequency radio control system.
The period of comparative stability which began in February 1945 ended in the opening week of March 1945 when the Allied armies initiated deep penetrations into enemy positions. Units at No, 72 Wing followed the territorial gains at maximum speed. The necessity for going as close to the advanced positions as possible in view of the rapid eastward movement led frequently to the existence of siting parties among the advanced units, awaiting the clearance of an earmarked area for immediate, siting and survey. Requests for the deployment of Oboe stations in forward areas resulted in expansion of the system parallel with that of radar navigation cover. After the Allied crossing of the Rhine on 24 March 1945 the ground forces surged rapidly forward and the Type 9000 units began to move into Germany to keep pace with the military situation. No 3 Type 9000 convoy, the first to arrive in Germany, left Florennes on 20 March and became operational at Kempenich on 24 March. On 10 April it again moved forward to Gotha from where operations began on 15 April. Nos. 4 and 6 Type 9000 convoys moved on top priority from Commercy and Tilboug early in April as they were no longer able to provide forward cover from those sites. No. 4 Type 9000 which was to proceed to a new site at Bad Homburg left the Rhine bridgehead on 3 April. Upon reaching the crossing, difficulties were encountered owing to the amount of military traffic of higher priority, and the American authorities refused to allow the convoy to go through. A discussion between SHAEF and General Anderson of the Ninth Bomber, Division resolved the situation, however, and the convoy moved forward on 5 April to become the first of the No 72 Wing units to cross the Rhine. No 6 Type 9000 convoy, which was scheduled for a site at Munster, then followed on 7 April, its crossing taking place without hindrance at the Wesel bridgehead in the British sector. No suitable site was found at Munster and the convoy moved to, and was finally deployed some twenty-four hours later at, Horstmar. Both stations became operational on 8 April 1945 when they were used for marking operations over Berlin for the first time, with reasonably satisfactory results. On 10 April No 5 Type 9010 convoy ceased operating at Rips and moved to Barntrup, where it became operational on 15 April. No 2 Type 9000 convoy had been retained at Laroche to provide cover over the Ruhr area, but after the 1iquidaton of the Ruhr pocket, the requirement ceased to exist, and on 16 April the convoy moved forward to Rottingen, becoming serviceable with the minimum of delay at the request of the United States Eighth Air Force. Only one Oboe convoy moved further forward, No 4 Type 9000, which left Bad Homburg on 26 April, and was operating at its new destination, Erbendorf, on 30 April 1945. Two operations were of particular note during this time, one which was successful and one which ended in complete failure. The first took place on 23 April when one of the largest Oboe attacks using continental stations was launched against Bremen. Nos 5 and 6 Type 9000 convoys at Barntrup and Horstmar were employed and 40 aircraft successfully bombed the target with a high degree of accuracy. On the second operation 16 aircraft were detailed to attack Berchtesgarden on 25 April, using the Type 9000 convoys at Molsheim and Gotha. The target was hopelessly beyond the range of the unit at Molsheim, however, owing to the screening effect of the Black Forest, and the operation was completely abortive. Although Headquarters No. 8 Group was aware of the limitations, the attempt had still been considered worth while.
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