There is no doubt that the crisis that was increasingly facing the German fighter force was made critically sharper by the `war of the radar sets’, and by the dropping of WINDOW strips in particular. As General Josef Kammhuber, German night fighter CO, said after the war, the time chosen for introducing WINDOW was exactly right-had it been earlier, the German electronics industry would probably have been able to produce a large number of radar sets immune to interference from it. In July 1943, however, the industry was so fully occupied, not least by the demands of the V-2 programme, that there was hardly any capacity left for the needs of the air war. In Britain, on the other hand, the manufacture of bombers and electronic equipment was reaching a peak, and only now making itself really felt. It was an area in which action and reaction came in swift succession. Every new method or tactic was soon countered. Gaining technical leads, short-lived though they might be, brought decisive advantages in the longer term. Radio and radar proved, however, to be two-edged weapons, which not infrequently were their own enemy.

This `war of the radar’ started in the first week of December 1942, when during an attack on Mannheim a 300-km MANDREL screen was deployed to jam and curtail the range of the FREYA early-warning system, and R/T traffic between ground control and the German night fighters was drowned out by loud noise generated by the RAF’s TINSEL device. During the raid on Dieppe, on 19 August of that year, the British had managed to get a closer look at the FREYA radar, discovered its operating frequency, and developed jammers that were already being tested by early September. The MANDREL jamming was circumvented by shifting away from the main jammed frequency, and ultimately by modifying the FREYA, MAMMUT, and WASSERMANN early-warning gears to operate on a lower frequency. Since German night fighters were able to detect aircraft carrying MANDREL, its jamming transmitter was always operated intermittently, for only two minutes at a time with similar intervals, which halved its effectiveness. This was also reduced by the fact that only 200, instead of 600, aircraft could be equipped with it. After a short while the operators of the long-range warning radars in any case learned how to `see through’ the MANDREL screen. The confusion caused among the German night fighters by TINSEL, however, lasted rather longer. Verbal instructions were misunderstood, or made incomprehensible, by the generated noise. To help the pilots hear what was being said, the power of the ground transmitters was turned up; in some cases the day fighters’ frequencies were also used, as the British were unequipped to jam these. Obviously not all the jamming could be overcome, but German countermeasures robbed it of a large part of its effectiveness. As a result British losses, which between December 1942 and February/March 1943 had fallen from around 5 to a low of 3.3 per cent, gradually rose again. The relatively simple and cheap MANDREL and TINSEL devices had, however, forced the Germans to convert their early-warning radars, and to install new R/T sets in their night fighters; this put a strain on the electronics industry, and saved the lives of around 100 RAF aircrews who would probably otherwise have been shot down.

The second unpleasant surprise in the early weeks of 1943 was the realization that British Mosquitoes, flying at great heights with a range of some 400 km, were able to drop their bombs blind on individual targets with great accuracy. For the time being there was no answer to this OBOE method (known by the Germans as `Bumerang’), as no sets had been captured and no transmissions plotted. It proved its efficacy and accuracy over Essen on 5 March and Wuppertal-Barmen in late May 1943.

The third great surprise for the Germans came in early February 1943 with the finding, in the wreckage of a downed Stirling bomber, of a centimetric airborne radar that gave a view of the ground; this became known to the Germans, from the place where it was found, as the `Rotterdam’ device. For the British its name was H2S, also known as PANORAMA because it displayed on a CRT the contours of the ground beneath the aircraft. Initially the purpose of the device was not clear, though it was suspected that it worked in the 8-cm band. The two surviving members of the aircraft’s crew refused to say anything about it, and this showed that it was something special. The find was a sensational one in that it overturned the conviction held among German radar scientists that hardly anything useful could be achieved in the centimetre wavebands, and then only at enormous cost-that it would be better to concentrate on the range between 50 and 240 cm, where current radars were providing most of what was wanted. The substantial echo given by aircraft in the centimetre band was largely unknown-quite simply, no one had so far taken enough notice of these frequencies. As a consequence of this conviction, Telefunken had in late November 1942 closed down its centimetre- wave laboratory. This had been done on the instructions of Gen. Fritz Erich Fellgiebel, general plenipotentiary for technical signals equipment, following a proposal from Dr Wilhelm Runge, Telefunken’s laboratory chief, and in the presence of Gen. Wolfgang Martini and Admiral Erhard Maertens, even though not all scientists and engineers shared this opinion. Martini himself had already, in the summer of 1942, recognized the need to develop radio valves for the centimetre bands, but at the same time had had to accept that because of a shortage of staff little could be done about it. Milch, too, had been pressing for copies to be made of Allied radar interception equipment.

One reason why, as Milch was aware, the German electronics industry lagged far behind its British counterpart was the suppression in Germany of the amateur radio movement, which had always had a great following in Britain. Under the Nazi regime it had always been suspected of espionage. `Anyone . . . with a radio transmitter’, according to Milch, `was 90 per cent ” certain to be a Moscow sympathizer.’ Now Goring too was complaining that `we smashed up the amateur radio “ham” clubs, and we made no effort to help these thousands of small inventors. And now we need them.’ The blame lay also, however, with the splitting-up of German radar research between the various parts of the Wehrmacht, the Reichspost, the universities, and electronics firms, as well as with how the far-too-unwieldy organization of the armed forces’ Ic intelligence dealt with radio/radar matters (in the Luftwaffe at least ten different offices were involved). Up to July 1943 it seems still not even to have been clear who in the Luftwaffe was responsible for high-frequency research ” and development, even though on 12 May Goring had, in something of a judgement of Solomon, given the Generalluftzeugmeister charge of the technical implementation of the radio and radar navigation programme, while leaving in place the powers of the head of signals communication matters, Gen. Martini, as general i/c signals. He no doubt felt that Martini did not have the right amount of drive, and naturally continued himself to take a hand in the “ring’s plenipo-matter. There was furthermore Staatsrat Dr Hans Plendl as Go tentiary for high-frequency research, who was given charge of the Reich office for high-frequency research set up on 16 July 1943.

In 1942 Germany had, in the radar field, only one-tenth of the research capacity available to the British, and it was spread over more than 100 small institutes. There was now a retrieval campaign to bring back to the laboratories around 1,500 scientists who had been sent to the front. After the middle of 1943 the number of scientists and engineers working on high-frequency research gradually rose to more than 3,000. The shortcomings in the centimetre-wave area were seized on by Heinrich Himmler, in criticism seen by younger qualified engineers as well founded, to approach Goring early in 1944 with the aim of launching a judicial inquiry. The grounds were that German industry and the military communications agencies were responsible for Germany’s inferiority in the high-frequency field, and for the ensuing adverse ” course of the war. Goring, with good reason, did not pursue this any further.

Radar Aircraft Warning Service

The keystone for centralizing the control of fighters, flak, and air-raid protection for the air defence of the Reich, and at the same time the basis for its functioning, was the aircraft warning service run by the Luftwaffe’s signal communications troops and acting as `the conduit for control operations’. It had to tell those in charge where the enemy’s attacking forces were, and where they were heading. Its development during 1943 was, while still not integrated, a continuous process. Since the start of the war there had been a series of radio-heterodyne cable networks providing the basis for the reporting service; these were not as vulnerable to eavesdropping as radio traffic, and provided the means of communication between the command HQs, airfields, flak HQs, filter centres, ARP warning HQs, and meteorology offices. The AWS also included the radar observation service, detecting transmissions from Allied airborne radars, IFF, and tail-warning radars; the enemy-aircraft movement plotting system; the jamming service, for disrupting enemy ground and airborne radar and R/T traffic; and-especially important for signals intelligence purposes-the radio interception service set up to listen in to enemy W/T and R/T transmissions and read their codes. Originally conceived as a strategic intelligence tool, it remained in practice only a tactical one.

The task of the radio intercept service, within the Reich air defence system, was to provide an up-to-date picture of the situation in the air over England, that is to say systematically to monitor and report on Allied com- mand, W/T, R/T, navigational, and air-traffic control transmissions. It was also required each day to discover impending attacks, by 1600h for any British night raids and by 1800h for American daylight raids (in each instance for the following night or next day), together with take-offs, assembly, and departure of their formations; it was also to report any changes in enemy deployment plans and cancellations of sorties. It further had to use various methods, independent of each other and of radar, for plotting the enemy’s track, and to assign the relevant radar stations and direct them via the observer service. Immediately after an Allied air raid, a combat report was to be made on the number of enemy formations involved, their strength, dispatch bases, landing bases, reroutings, losses, and damage suffered.

For XII Air Corps the processing of all this information, coming in reports ” from a large number of other stations, was carried out at the Seerauber (`Pirate’) radio-monitoring message centre located at Zeist in the Netherlands.

While an enemy incursion was under way, the aircraft warning service had to determine the situation in the air at any time as quickly as possible, exactly and comprehensively, and pass this information on to the fighter units, flak, and ARP warning service. To do this it was divided into aircraft warning companies, each comprising a filter centre and a ring of observer posts feeding reports into it. Broad-area observation was served, along the coasts and later inside Germany as well, by long-range radars of the WASSERMANN and MAMMUT types; these had ranges of 150 to 250 km, which allowed them to detect enemy aircraft flying at 7,000 m as far away as central England, and ” plot their course. Apart from these, the WURZBURG and longer-range FREYA radars formed the AWS’s standard equipment. Because of the shortage of radar sets, there was still in August 1943 a large gap in coverage along the old border of the Reich in south-west Germany; enemy formations approaching over France `disappeared’ into this hole, and were able to make dramatic changes of course quite unobserved. It was, in particular, very difficult, with the RAF employing ever more resourceful tactics, to tell the difference at night between main, nuisance, and spoof raids and feinting manoeuvres and to alert the fighters soon enough and deploy them at the right time and place. The reporting system using teleprinters entailed considerable delays in the information getting through. With the enemy aircraft flying increasingly higher and faster, the AWS was becoming barely able to fulfil its task. The FREYA early-warning radars were frequently being jammed by enemy transmitters when the British made their night raids. Furthermore, other radar sets, like the flak’s gun-laying radars, were being blinded by the strips of metal foil. In October 1943 the 8th Air Force on its daylight raids, too, began ” jamming the WURZBURG sets with airborne transmitters in the 40 to 70 cm band and from 26 November additionally with CHAFF, while at the same time switching to bombing through cloud without sight of the target using the H2X ground-mapping radar. In daylight and with good visibility the aircraft warning service was indeed able, using optical and acoustic means (sound locators), to determine the position, aircraft type, and strength of enemy formations and their speed-something the radars were not always capable of; but in poor visibility it often (in the opinion of Gen. Wolff, the Luftwaffe commander for Luftgau Hamburg) failed, mistaking its own fighters for enemy bombers. All this jamming and these shortcomings not infrequently made it hard for the AWS to arrive at an accurate picture of the situation in the air. Ultimately, the situation reports flowing into Luftgau headquarters came from three different sources: alongside the AWS the flak artillery, with its ” WURZBURG and FREYA tracking and gun-laying radars, also provided a picture of what was happening, though mostly only a local one; and the night-fighter force with its control system provided a rather wider view across the areas it covered. Co-operation between these various participants did not always work. During bombing raids the lines of communication between them and the individual radar sites and observer posts could be severed. Moreover, the radar plotting networks of the three organizations contributing to the overall picture had developed differently. Insufficient production meant that the aircraft warning service was initially treated as the poor relation when it came to allocating radar equipment; the lion’s share went to the flak and to the central fighter division operations rooms, fully expanded by 1943, at Deelen, ” Stade, Metz, and Doberitz, and the fighter control operations rooms at Schleißheim and Vienna. More and more the building up of a broad-area picture of the situation in the air came to be based on these operations rooms, which drew their information from the superbly equipped night-fighter stations reporting to them. The Reich aircraft warning service came more and more, through the direct link between its observer posts and the fighter operations rooms and night-fighter stations, to take on a customer role, no longer at all independent and now merely passing on information on the situation to the air-raid warning service and civil ARP authorities.

In late August 1943, at a meeting on night fighters, Milch stated: `I get very much the impression that the whole aircraft warning service ought to be overhauled from top to bottom . . . that it is a thoroughly out-of-date set-up. ” Gen. Martini acknowledged that in the provision of FREYA and WURZBURG radars the AWS had been neglected in favour of the flak and fighter commanders. Now, as Luftwaffe Commander Centre had asked, ten out of the 40 FREYAs produced in September were to be allocated at once to the AWS. Improvements would be made: the network of observer posts would be strengthened, small filter centres set up linked to the night-fighter HQs, wide- area coverage created by merging several filter centres, and the transmission of information speeded up (by replacing land-line teleprinter communication by telephone links or radio reporting). These measures were decided on at ” the meeting with Goring on 25 September 1943. On the question of subordinating the AWS opinions were, however, still divided. The generals in charge of day and night fighters, Galland and Kammhuber, agreed with ” Goring in wanting it placed under the fighter command. Maj.-General Schmid of XII Air Corps/I Fighter Corps, Maj.-General Schwabedissen, commander of 5th Fighter Division, and Lt.-Colonel Herrmann were against this, though they wanted the right to issue orders and receive priority service.

Generaloberst Weise argued for it to be placed under the Luftgau commands. Goring came to no decision, though he wanted the fighter commanders to have preferential and comprehensive treatment.

Gen. Martini had already made a start on strengthening the aircraft warning network in the spring of 1943. He did so step by step, beginning with areas through which the Allied bombers were mainly passing-Luftgau VI (Munster), the Netherlands, western France, Luftgau XI (Hamburg), and so on. In Luftgau VII (Munich) the new organization was introduced on 6 December. In the areas of maximum effort the number of observer posts was increased, in particular through setting up small filter centres attached to the fighter defence’s radar sites in order to complement or replace the radar contacts with visual/acoustic detection if the radars were put out of action by jamming. Martini had thus stepped up co-operation between the fighter controllers and the aircraft warning service. He further instituted three levels within the system-small and main filter centres, plus a wide-area coverage by combining several main centres at the Luftgau or flak division HQs. The `commentary’ system too had, because of the radar interference from WINDOW, already been used for the first time by the fighter controllers during the Hamburg raid on 27/8 July. To obtain an overall picture of the situation across a wide area, Martini had FREYA `hedgehog’ sites (comprising three radars each covering a 120-degree arc) set up at effective points. And as has already been mentioned, flak-fire director officers had been attached to fighter-division HQs to provide better co-ordination between the flak and the fighters. The fighter command further tried to overcome the difficulties caused by the inadequate performance of the aircraft warning service, and by the jamming of radar, through the use of radio/radar DF stations, which were able to plot the enemy’s track. The KORFU radars, for instance, could locate aircraft using H2S so long as this was switched on, and the NAXOS gear could pinpoint British aircraft carrying the MONICA tail-warning radar. The FREYA radars were also used in the `Flamme’ method (by triggering IFF responses from the British aircraft) mentioned earlier. The range of this UHF technique depended on altitude, and with aircraft at 10,000 m could be 360 km. The `Flamme’ reports soon took on great importance for determining the situation in the air. Many gaps in the overall picture over Germany were filled in by the use of air-reconnaissance aircraft, and by the JAGDSCHLOSS 120-km-range panoramic ground radar introduced in 1944.

The relationships in the whole field of aircraft reporting and warning that ” had formed by this time were enshrined and given basic structure by Goring’s order of 28 February 1944,337 by which achieving `an integrated overview of the situation in the air . . . by removing the aircraft warning service from the Luftgau headquarters’ brought about `the organizational and operational amalgamation of the aircraft warning and aircraft tracking services . . . in integrated fashion . . . under the headquarters of the fighter commanders’. The fighter divisions and fighter controllers, who had long had the fullest and earliest overview of the situation in the air, thus became the central points at which knowledge of the situation coming from all sources was pooled; they became responsible for providing the overall and up-to-date picture. These sources were, to list them once again, mainly the radar organization, the air- craft plotting and warning organization, the radio/radar monitoring service, and the air-reconnaissance aircraft flying by day and night. From now on the sole means of passing the reports within the aircraft warning service and to the end-users was the `commentary’, and no longer the written word. The density and depth of the observer post network was laid down by the fighter commanders; they were to be sited around 30 to 40 km apart, and it was planned to have them closer together along the coasts and fronts. At the same time it was intended that they should no longer be arranged in belts or rings, but be spread out and partly overlap. Deep inside Germany they were to be set up in important areas and sited at the best possible vantage points complementing the radar network which, where it was placed in hilly terrain, gave only imperfect coverage. They were not only to scan the skies with eyes and ears (for which they were to be given the right optical and acoustic equipment), but also-especially when jamming put the electronic devices out of action-to track the low-level intruders who in 1944 were becoming increasingly com- mon. They were further responsible for identifying the enemy aircrafts’ target, determining the make-up of their formations, and reporting on their course and the target indicators and bombs they dropped, as well as for observing the Luftwaffe’s own aircraft. Because of these functions, observer posts were always to be linked to the aircraft warning centres of the nearest radar sites. These centres formed the first picture of the air situation for a limited area, compiled from visual and aural observations and radar contacts. The AW centres within a given AW sector were in turn to link in with the assessment carried out at the fighter operations rooms. They thus became AW sector centres, taking over the tasks of the earlier filter centres. The AW sector centres then reported to the operations room of the fighter division in whose area they were located. Within the divisional AW centres the findings flowing in from the radio intercept service and air reconnaissance, and their own view of the situation, were brought together to form a picture of the situation in the air. The air fleets had liaison units supplying them and all the other end-users (in particular the flak and ARP warning service) with the division’s overall assessment. For this purpose there were with them, as with the fighter corps, AW centres supplied with a situation overview by means of commentary from the fighter divisions.

There were now first-rank radar sites forming the basic network of aircraft warning service. Each of these were to be equipped with a new JAGDSCHLOSS 360-degree panoramic search radar, with a radius of around 80 km. With these set up at intervals of 150 km, it was reckoned that 125 would be needed to cover the whole of Germany and German-occupied territory; only 15 were, however, in operation by the time the war ended. The first-rank radar stations within the Reich were to be equipped with a panoramic search radar, a long- range search radar (both of these, until such time as they were delivered, to be ” replaced with a FREYA), a further FREYA, one or two GIANT WURZBURGs, and a SEEBURG plotting table, where they were also to be used for `dark’ night-fighter operations in the `Himmelbett’ system. Along the coastal fronts the intention was to provide each of them with one or two long-range FREYAs and GIANT ” WURZBURGs and a SEEBURG table whenever they were involved in `dark’ night- fighter operations. In each instance an observer post was included. Later on, Y, EGON, KORFU, and NAXBURG gears were added. A radar station could, if suitably located, be used as an AW sector centre. Because of the fairly limited ” range of the WURZBURGs, second-rank radar stations were set up to provide a denser network in areas particularly subject to air-raids; these had no long- range radars, and were less generously equipped. They were also allocated observer posts, and the associated AW centre was similarly second-rank. In addition to these there were also third-rank sites and centres, all feeding their reports into a first-rank one.

The fighter divisions produced the sole air-situation report, the use of which was obligatory for all; this ended the coexistence of three different views of what was happening in the air (from the fighters, the flak, and the Luftgaue) and the confusion that often resulted. Yet shifting the responsibility onto the fighter-division operations rooms also created difficulties, as these did not at once have the appropriate personnel to cope with the additional duties; the new system was not equally successful everywhere. Nonetheless, the delay in passing the information could be cut to a matter of seconds, since all reports from all sources were immediately displayed graphically on a plotting table, and errors and duplicated reports avoided. The commentary system meant that observation, reporting, assessment, and forwarding of the information happened in quick succession. Using common land-line and radio links, fighter-division officers-articulate and with a clear enunciation-simultaneously passed information to the headquarters of Air Fleet Reich and I Fighter Corps, the Geschwader under them, the Luftgaue, the flak divisions, and the ARP warning centres and AW sector centres. The decimetre-wave radio network was immune to enemy interruption.

The backbone of the aircraft warning organization was provided by the FREYA radars, which had a range of some 120 km and were less vulnerable to jamming. The most far-reaching surveillance came from the WASSERMANN and MAMMUT radars, with ranges between 200 and 300 km. The JAGDSCHLOSS panoramic search radar had an enhanced resolution in range and azimuth, and ” was particularly suited to detecting low-flying aircraft. The GIANT WURZBURGs were the standard gears for altitude ranging, fighter control, and flak location and gun-laying tasks.

The further expansion of the new AW system needed a great deal of time, and was hampered by the loss of the forward areas in the west and south (and there also by the geography and terrain). In general all went well, but Gen. Martini was still in November 1944 complaining that the reorganization ordered at 7th Fighter Division and in East Prussia had not yet been carried out, and that the order on restructuring had not even been communicated to Air Fleet 6. A link between 1st Fighter Division in Berlin and 8th Fighter Division in Vienna, needed for exchanging information about flights out of and into their areas, still did not exist. The area of the Alps was not adequately covered, so that most reports coming from the south were reaching 7th Fighter Division in Pfaffenhofen too late; in that area the JAGDSCHLOSS sites were often being put entirely out of action by a heavy use of WINDOW. A drain of personnel being transferred to the army was getting in the way of forming a clear picture of the situation in the air, and slowing down the passing on of information to the Party’s Gau headquarters (though this was less important compared to the operational needs). Implementing the concept of restructuring the aircraft warning service, ideal in itself, was besides meeting with fresh technical difficulties.

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