Cipher Department of the High Command of the Luftwaffe

The great widening of the battle front and the prodigious expenditure of men and material forced the German Command, following the first grim winter in the Soviet Union, to adopt radical economy measures. Thus, the Luftwaffe Signal Corps, that had suffered relatively slight losses, was referred to the pool of women workers for its replacements, as the men were being stripped from Luftwaffe units for the front.^[36]

The importance of radar intercept, moreover, that by the middle of 1942, had finally become production ready, had become decisive to the development of the Chi-Stelle in the west and caused significant structural changes. At the same time, as German strategy swung to the defensive, the Chi-Stelle emerged as the most reliable source of radio intelligence. As the Allied air offensive unfolded, its importance to the defence of Germany became apparent, not only to the High Command, but to tactical headquarters as well, and from then on, both were concerned that its organisation become optimal. From the beginning of the war, command of the Chi-Stelle unit had changed hands frequently, with unsatisfactory leaders.^[36] The Luftwaffe General staff officer Ferdinand Feichtner who was considered to have an excellent reputation with the General Staff, took command of the unit in February 1943.^[37]

At the same time the Chi-Stelle, at least in the west, was freed from the administrative management of the signal regiments of the Luftflotten by the creation of an independent Signals Intelligence regiment. This regiment had three battalions, one of which was devoted exclusively to radar intercept. This stronger centralisation had a favourable effect on future development. The number of impediments to which a relatively young branch of the service was inevitably subjected was considerably reduced by the excellent relations between the Commanding Office of the Chi-Stelle and the General Staffs.^[38]

At the end of 1942, the Radar Intercept Control Centre was created in Eiche for the central evaluation of the results of radar intercept. Radar intercept centres were also brought into being at the same locations as the W-Leit of the Luftflotten, and gradually within the boundaries of Germany itself. Chi-Stelle determined policy, and planned the expansion of the Radar Intercept Service, while the development of processes was left to the out-stations and the commanders of the Referat. In this aspect, Chi-Stelle purpose was essentially one of administration and supply.^[38]

The Chi-Stelle from 1943 was no longer distinguished by creative ideas. The choice of an officer with no signal or intelligence training as Director of so highly specialised a service was not a fortunate one. Briefing of the General Staff was the direct function of the Referat. Each Referat chief, in proportion to his ability, made the influence of his Referat felt on the evaluation work of his respective Leitstelle. Except for personnel and administrative matters, those Leitstellen which were capably commanded were completely independent of the Chi-Stelle. An example of this separation of concerns was that many times they even procured special signal equipment or communication facilities from the tactical units they served, rather than go through the normal Chi-Stelle channel.^[38]

The Chi-Stelle also failed, when the time was right, to mould the unit into a comprehensive and exclusive organisation with its own military standards. On the contrary, in autumn 1944 when signals regiments were formed in the west, south and east, bureaucracy intervened to create two extraneous posts. The first one was a Signal Intelligence Director for administrative matters, the second new post was that of Signals Intelligence Leader (German: Funkaufklärungsführer Reich), pertaining to the defence of Germany.^[38]

The structure of Chi-Stelle was essentially the same since the beginning of the war and had developed along two main lines. Tactical evaluation from 1943, had become predominant and had resulted in the establishment of early warning and flight tracking systems.^[38] The development of tactical evaluation was fostered by the increasing strength of Allied air raids on both the occupied countries and Germany, and it far exceeded the importance of strategic evaluation. This work culminated in the creation of the ZAF [Ref 3.2.4], a central Meldeköpfe for the defence of the Reich. The Chi-Stelle remained both indifferent and helpless in the face of this development, with the result that the position of Chief Signals Intelligence, a parallel headquarters had to be created to manage signals matters pertaining to Germany. Secondly, the unification of the Chi-Stelle, that by 1942 had expanded into an organisation of division strength and was urgently in need of an independent administrative system in consideration of its special function, finally in 1944, proved most necessary. Discussions to solve this problem had begun in 1941, but postponed continually.^[39] However, since Chi-Stelle planned and supervised all signals intelligence operations from the beginning, it could easily act as its own central administrative authority. In the spring of 1944, the first of these reorganisations took place. All signal intelligence units including the Chi-Stelle which previously had been under the command of the Ministry of Aviation, were now placed under the tactical command of the Chief Signals. 3rd Division, Lt. Colonel Ferdinand Feichtner whose rank was (German: Generalnachrichtenführer) (General Nafue III).^[40]

This centralisation in tactical matters and the decentralisation in administrative affairs to the field command units led to difficulties in guidance and supply. As a result, in November 1944, after an abortive order by Hermann Göring to unify all Luftwaffe signal intelligence units through combining all listening, jamming and radio traffic units as part of Air Signal Regiments, a new comprehensive organisation was finally created.^[40] This new organisation unified all home and field units into independent air signals Regiments and battalions with unit numbers ranging from 350 to 359. The administration was centralised and subordinated to a Senior Signal Intelligence Officer, Generalmajor Wilhelm Klemme, a veteran signals officer, who held the position of (German: Höherer Kommandeur der Luftnachrichten-Funkaufklärung).^[40]

From 1941 to 1944 the signals intelligence battalion in the Marstall consisted of:

• A company in the Marstall which comprised the personnel of Referat A, C and E.^[39]
• A company in Asnières-sur-Oise comprising the personnel of Referat B, part of the personnel of Referat E and an intercept platoon.
• A company in Žitomir, later Warsaw, comprising personnel of Referat D and a large intercept platoon and Meldeköpfe.
• A company in Munich, Oberhaching comprising personnel of Referat B5 and an intercept platoon to monitor the United States.^[41]
• An intercept company in Rzeszów which monitored Soviet point to point traffic.^[41]

After the withdrawal from France, the company in Asnières-sur-Oise was dissolved and Referat B greatly reduced in personnel, was migrated into the evaluation company of signals intelligence regiment west. The company in Rzeszów which had moved to Namslau in the middle of 1944, was transferred to the signals intelligence regiment east, and for practical purposes, it already belonged. Referat D was incorporated into the evaluation company of this regiment when the latter left Cottbus and retreated to the southwest while under attack from the Soviet advance. In February 1945, the Marstall was abandoned.^[41]

In the autumn of 1944, the Chi-Stelle battalion, as had been the case with of all signals intelligence battalions, became independent of the Luftwaffe Signal Corps Regiment to which it had been assigned. Command was taken over by a captain who was given the prerogatives of a regimental commander. It was renamed Air Intelligence Department 350 (German: Luftnachrichtenabteilung 350) and retained its previous function of planning for the entire Luftwaffe signals intelligence infrastructure. In reality, the command structure, and unit organisation had not changed at all, in spite of the battalion commander, Captain Jordens, the administrative chief, General Klemme, and the Funkaufklärungsführer Reich, Colonel Forster, Lt. Colonel Ferdinand Feichtner as the representative of the Chief Signal Officer, remained the supreme authority until the end of the unit.^[41]

The Referats were the supreme authority on all evaluation questions arising between the regiments, battalions and the Chi-Stelle. They furnished intelligence directly to the General Staff where a liaison officer had been assigned since 1942.^[42] Section II of the Office of the Chief Signal Officer only had communication with individual units insofar as to pass the orders. The final preparation of reports decided by Referat. The responsibility for distribution of the reports was decided by the Chi-Stelle Director who acted in consultation with the Chief Signal officer.

Liaison with B-Dienst, the Kriegsmarine cipher bureau and General der Nachrichtenaufklärung, the German Army cipher bureau, as well as the Radio Defense Corps was carried out at both the level of the Referat and at the Leitstellen, which exchanged reports with Navy and Army cipher bureaux located in their respective areas. However, owing to the extreme secrecy which surrounded all activity at the unit, the process of exchange was not perfect. For example, the liaison between the Luftwaffe and the Radio Defense Corps regarding Yugoslav Partisan activity in the Balkans was founded on the relationship between two Leutnants, who despite instructions to the contrary, exchanged intelligence on this subject.^[43]

The three cypher bureau (German: Chiffrierstelle) exchanged reports, and in the case of the Luftwaffe, these were studied by the individual Referat. From 1942, a liaison officer from Referat B was assigned to the Army Chi-Stelle in Saint-Germain-en-Laye but no special benefits were derived from this close association.^[43]

Chi-Stelle decided the extent of co-operation and liaison between Germany's allies, but the execution of process was decided by the signals intelligence units located in the various countries.^[43]

The Finland cypher bureau, the Signals Intelligence Office (Finnish: Viestitiedustelutoimisto) was the only bureau within the Axis, that compared with Germany in terms of quality and had made excellent progress on the cryptanalysis of Soviet (Russian) systems.^[44]

Liaison with Japan did not exist, and contact with the Japanese on-air signal intelligence could only take place through the General der Nachrichtenaufklärung, that received the monthly reports of the unit. It would seem probable that the Japanese signals bureau would be interested in reports of special fields, such as the 8th USAAF or Allied navigational procedures, that would have been furnished by the GDNA. In the last year of the war, and at the request of the Japanese, it was intended to send a German mission, comprising medium frequency and high frequency specialists to Japan. Strangely the Japanese were not interested in VHF or radar interception and jamming.^[44]

When the Chi-Stelle was taken over by General Staff officer, Ferdinand Feichtner in the spring of 1942, it resulted in the Lietstellen being supported in a previously unaccustomed manner.^[44] In order to meet the increasing demands within the unit for personnel and equipment, the Chi-Stelle initiated a strict management control policy. The development and procurement of radio receivers was also problematic and involved negotiations with the manufacturers, who with long supply chains demanded notification of orders long in advance. Problems with personnel bounded, with the personnel officer whose only experience was the Eastern Front, while Rudolf Friedrich's staff did not have one officer who had experience of working against the Anglo-American Allies.^[45] Therefore, the Chi-Stelle command had little understanding of the problems existing in the west and south. The problems were compounded by individuals who lacked tactical experience, particularly Captain Trattner, Commander of Radar Intercept at LN Abteilung 356, who was a professor of electronics. It can be stated that Referat A had a short-sighted policy as regard to personnel, as well as an indecisive and dilatory manner when it needed to handle personnel problems affecting the entire unit.^[45]

In contrast to other units and sections of the Chi-Stelle, Referat B maintained a constant and purposeful policy towards its own personnel. When the former Director of the unit was ordered back to the Marstall in mid-1942, his place was taken by a career officer who removed the last vestiges of the civil service regime from the Referat.^[46] Daily conferences and a number of experienced combat officers were brought in and employed to advise the evaluations in the various desks. The personnel of the Referat were now continuously trained and were accorded all privileges possible with military functions, such as drilling kept to the minimum. As a result, morale in the unit was considered excellent.^[46]

At the end of 1942, some of the personnel were replaced by women auxiliaries. Shortly before the Normandy landings, the Referat consisted of 4 officers, 3 technicians, 45 enlisted me, and 25 auxiliaries.^[46] After the withdrawal from France in August 1944, the Referat was merged with the evaluation company of Signal Regiment West. Personnel were reduced by more than half. At the end of the war, with the advancing Allies, the unit moved to Türkheim in Bavaria when it was subsequently dissolved.^[46]

Allied traffic intercepts increased significantly when the RAF expanded from 1942 onwards, and the arrival of American Air Forces in the British Isles.^[47] This resulted in a reorganisation of Referat B, which was gradually implemented during 1942. Later the desks of the Referat were organised to correspond to Allied air unit categories, rather than types of radio traffic. The organisation was as follows:

• Technical evaluation section which evaluated RAF Coastal Command intercept and during the Normandy landings and with air support, evaluated intercepted party traffic.
• Bomber evaluation section, divided into Royal Air Force and United States Army Air Forces desks, which were concerned with the strategic evaluation of this traffic.
• Captured documents, captured signal equipment and navigational aids, evaluation sections.
• Tactical air force radio traffic evaluation desk.

The Referat has its own mimeograph and technical drawing section. The teleprinter and telephone section was operated exclusively by women.^[47]

Referat B was the senior evaluation agency in the west, and evaluated all the work of the signal intelligence units employed in the west and the north.^[48] This consisted of:

• Luftnachrichten-Funkhorch-Regiment West that later became LN Abteilung-Regiment 351
• LN Abteilung-Battalion 357
• LN Abteilung-Battalion 355

The Referat worked with reports forwarded to it from intercept and evaluation companies, and also with the original log sheets and messages. The latter method was used for Radio telegraphy, as the spoken word was always open to interpretation. The material available to the Referat consisted of the following:

• Daily reports from evaluation and some intercept companies, that were sent by teleprinter and in some most cases by radio or courier.^[48]
• Technical and evaluation reports which the intercept companies prepared monthly.^[48]
• Wireless and Radio telegraphy log sheets.^[48]
• Prisoner of war interrogations' reports, reports on captured documents and kit. Reports on BBC broadcasts and other collateral intelligence material. This interpolation of this material was strictly forbidden, and when used, a reference was provided to the source and if this was missing a reprimand from Ic operations to the Referat chief resulted. It was provided to bring a richer background to intelligence reports.^[48]

It was advantageous that personnel of Referat B belonged to Chi-Stelle as intelligence could be reported or when necessary refused to be divulged under certain conditions without reference to rank or station. The last two chiefs of the Referat were adroit at using their position to maintain a close check on the evaluation work in the west.^[49] Duplication of work between Referat B and Luftnachrichten-Funkhorch-Regiment West was an ongoing bureaucratic problem and the only considered solution was the merging of the two units, but it was only realised as the result of Allied pressure, when both Referat B and Luftnachrichten-Funkhorch-Regiment West, following a breakthrough by the Allied at Avranches as part of Operation Cobra by the United States 1st Army, retreated from France. Owing to the difficult housing situation within Germany, the Referat and the evaluation company were established in the same house in Limburg. For each case arising, a discussion took place as to whether a special report or appreciation would be written by the Referat or the specific company from Luftnachrichten-Funkhorch-Regiment West.^[49]

Outside of final evaluation, the direction of intercept cover in the west and north was the most important task for the Referat. All intercept stations understandably had the desire to monitor only that traffic which yielded results.^[49] The Referat had to insure that not only was this traffic covered but also those frequencies necessary to obtain a correct intelligence estimate.^[49] For example, several intercept companies could only be moved under pressure to monitor point-to-point networks of the RAF and the Allied Expeditionary Air Force, as no tactical messages that could be reported to combat units were intercepted on those networks. However, these networks still had to be monitored, as it was necessary to understand the organisation of Allied air forces.^[50]

With the appearance of new allied units which needed to be monitored, intercept companies found it difficult to burden themselves with the intercept requirements of the new allied units. In that instance, Referat B would intervene, and reorganise the intercept and evaluation companies accordingly, as per need and personnel available.^[50]

In many cases Referat B itself would take over the analysis of new traffic, and only then would they subsequently assign it to the appropriate evaluation company.^[50]

The most important headquarters to which the Referat reported were:

• The Luftwaffe General Staff, Oberkommando der Luftwaffe.^[50]
• The Chief Signal Officer of the Luftwaffe.
• The General der Nachrichtenaufklärung, the signals intelligence agency of the Oberkommando der Wehrmacht.
• The B-Dienst, the German Naval Intelligence Service of the Oberkommando der Marine.^[50]
• Luftflotte 5
• Referat C, for those units working in the south.

In many cases reports were also sent to the commander west, Luftflotte 3 and NAAS 5 of Army signals intelligence regiment KONA 5.^[50] The following types of messages and reports were involved:

• Flash reports of important new discoveries, movements of Allied units, that were sent by telephone and teleprinter.^[50]
• A 24-hour daily summary report.^[51]
• Monthly reports comprising 50–60 typewritten pages of exhaustive treatment of all events and developments during the month, complete with maps and illustrative diagrams.^[51]
• Special reports, e.g. on Army-Air Force collaboration during manoeuvres in the Great Britain.^[51]

Moreover, all important information found in captured material was communicated to individual signals intelligence units. The latter received from Referat B all necessary data such as lists of X and Q groups, lists of frequencies, call signs, abbreviations and so on.^[51]

In 1941, a section within Referat B was established to monitor and intercept traffic from the United States. This, in turn, was divided into two desks. One desk analysed traffic which was related to United States Army Air Forces, the other to United States Navy air forces, which at the time were being hastily built up. Traffic from America was ready from intercept stations in Germany, France and Norway. The desk reached its peak in late 1942, early 1943, when new equipment was becoming scarce and this dictated a more conservative use of radio receivers. The second section desk intercepted air ferry traffic on the North Atlantic route, in connection to RAF Coastal Command. The Atlantic traffic was monitored by Referat C until 1942 when it reached peak importance. As the war progressed, and United States cryptography steadily improved to an extent it could no longer be read, Referat B took responsibility of this South Atlantic commitment from Referat C.^[51]

As Allied air ferry traffic increased in importance it was decided to detach the desk from Referat B in mid-1943, and move it into its own section. Specialist personnel from Referat C were moved to Oberhaching and the new section was renamed Referat B5.^[51] At the same time a large wireless telegraphy intercept platoon that belonged to the Marstall battalion, was moved to Oberhaching and attached to Referat B5 to take over monitoring of air ferry traffic except those on North Atlantic route, which were covered by the 16th Company of Lichtenstein Regiment (LNR) 3 in Angers.^[52] The new Referat evaluated all air ferry traffic, e.g. Morse code, Baudot code, and had the following responsibilities:

• The monitoring of the United States, which only touched the surface of the traffic, still furnished insight into the principal networks of the Army and Naval Air Forces, into training activity, air transport, defence zones, and the activation of new combat aviation units.^[52]
• The monitoring of Atlantic air ferry service. The middle and central Atlantic routes were monitored by the W/T platoon in Oberhaching and by Luftwaffe signals outstations in Spain, which operated under the cover-name of Purchasing Agencies (Fig 3). The North Atlantic route was monitored by the 16th Company of LNR 3 and reported furnished to the Referat.^[52]
• The monitoring of the United States Air Transport Command by the platoon in Oberhaching.
• The monitoring of the RAF Transport Command and both USAAF and RAF troop carrier command. The greater part of this interception was also carried out in Oberhaching.^[52]

Airfield radio traffic, transmitted on 6440 Hz was intercepted in Madrid, Montpellier and at various outstations in the Balkans and Italy. This traffic was evaluated by Referat B5 with the aid of an extensive intelligence library encompassing charts, diagrams, directories, manuals, maps, phone directories and so on.^[52] Referat B5 also had a small cryptanalysis section of its own, which deciphered intercepted messages on the spot.^[52]

Referat B5 remained operational until the last weeks of the war and was in a position to cover the British airborne landing at Bocholt.^[52] One week before the capture of Munich by the US 20th Armored Division. US 3rd Infantry Division, US 42nd Infantry Division and US 45th Infantry Divisions, the male members of Referat B5 withdrew to the Alps, while its women auxiliaries were discharged.^[52]

When the importance of the Mediterranean Theatre increased in the middle of 1942, the totally incapable director of this Referat was relieved from office at the instigations of General Staff operations, and replaced by the director of Referat B.^[52] At the same time, several experienced evaluations were transferred to Referat C in order to mentor and assist new staff and this served to increase morale in the unit. In general, the operational methodology of the unit was similar to units in the west.^[52] In spite of wire communication to Sicily and Greece being considered reliable, the great distances to the Mediterranean theatre presented problems. The tactical evaluation was lacking and daily reports were always two days behind schedule.^[52]

Referat C was considered unproductive, inefficient and bureaucratic. During the entire period of its existence it failed to produce a single technical or special report, in spite of the fact there was sufficient material from activity in the Mediterranean area. In early 1943, the number of personnel in the agency was increased with 20 women auxiliaries, with the emphasis shifted entirely to paperwork.^[53] During this period the agency was completed detached from problems in the Mediterranean area.

This condition became worse in 1944–1945 as duty hours were increased, rations became fewer and bombing raids became more frequent. The prevalence of political sycophants, the threat of being sent to the Eastern Front, the threat of transfer via disciplinary action, all served to suppress and curb the agency personnel working 12 hours or more a day. Messages and reports from the retreating signals units in the south became scarcer and scarcer.^[53] After the formation of Luftnachrichten Abteilung 352 in spring 1943, a merger of the Referat and the regimental evaluation company was considered, but never carried out. In February 1945, the unit disbanded, with parts of the unit travelling to Premstätten in Styria and later in Attersee. Although reduced in size, it started to work again under command of a new energetic director. However, this was short lived and in May it ceased activity.^[53]

Referat C was organised into desks which corresponded to Allied units or activities, e.g. Mediterranean Allied Tactical Air Force (MATAF), 205 Group RAF, long-range reconnaissance, radar reporting networks, transport and ferry service, airfield radio tower traffic.^[54] In addition, two other sections, one devoted to press reports and prisoner of war intelligence, and other to point-to-point networks were especially successful. The two sections, in close co-operation, maintained a detailed organisational plan of Mediterranean Allied Air Forces (MAAF), that the Luftwaffe operations office included in its monthly reports.^[54]

The following desks were attached to Referat C:

• Turkey. Three men revised and edited the material intercepted and evaluated by W-Leit South-east, and prepared weekly and quarter-yearly for operations.^[54]
• Sweden and Free France. Monitored by outstations with monthly reports were forwarded to operations. After the German withdrawal from France, the desk was reintegrated to Referat B.^[54]
• Referat C2. This section was created in 1942 and was engaged in preparing a textbook on the radio, navigational procedures and call signs of the Royal Air Force, United States Army Air Forces and Russian Air Forces. This textbook has a wide distribution, and all larger signals units were given copies for research. Supplements were produced which kept the work up to date. In mid-1944, the work was abandoned and the personnel transferred to signals outstations.^[54]

An intercept station also existed in the Marstall itself and was manned by linguists from Referat C and E. Its primary function was to monitor and intercept traffic that indicated a bomber raid in the greater Berlin area by the USAAF. As the Marstall was responsible for the allocation of VHF receivers, the equipment in the intercept station was the best of its type.^[55] The proximity of the Referat proved advantageous, as the R/T technicians manned their sets only during a bombing raid and therefore could devote the balance of their time to either evaluation or cryptanalysis.^[55] Flash reports were telephoned to Meldeköpfe 3 stationed in Wannsee, while final evaluation reports were sent to the ZAF.^[55]

Each morning the teleprinted material arrived during the previous night from the two signal battalions in Italy and the Balkans,^[55] from the company in Montpellier, outstations in Spain, and later from the ZAF, as well as from those outstations which were authorised to have direct communication with the Referat. The intercepted material was sorted, categorised by the Referat director and distributed to the appropriate desks.^[55] In the course of the afternoon, the desk would check the incoming intercept. If it could be read, it was solved and evaluated immediately. If it could not be, it was sent to cryptanalysis. Deciphered reports were prepared for inclusion in the daily report of the Referat. After being edited by the evaluation officer, the intercept formed the basis for the daily situation conference at which all controversial points were discussed.^[55] It was then Mimeographed and around noon it would be ready for distribution. One copy was sent by courier to the General Staff, the others were mailed to the recipients.

The afternoon, as a rule, was devoted to the study of incoming reports and a review of log sheets in from the units in the field; maps were prepared and preliminary work was done on the monthly report, the distribution of which corresponded in principle to that of Referat B reports.^[55] Correspondence with the regiments and battalions was taken care of, comments from the General Staff were studied and those relevant were passed on to the field units concerned.^[55]

The Referat achieved success in the field of traffic analysis. By means of network diagrams, the organisation of the Allied tactical air forces in Italy was worked out at a time when W-Leit 2, in spite of its greater proximity to the situation and its operational experience with abundant wireless telegraphy (W/T) and R/T reports of XII Tactical Air Command and Department of the Air Force (DAF), was completely helpless.^[56] In general, like clumsiness, distrust and dodging of responsibility characterised the leadership of Referat C. In order to keep its surplus of personnel occupied, ridiculous and unnecessary tasks, involving a labyrinth of paperwork were created. As a result, all feeling for conciseness was lost. The majority of members of the Referat, in spite of years of service in the Chi-Stelle, had never seen an out-station. This reluctance to face realities weakened the influence of the Referat.^[56] In consequence, its options in organisational matters carried little weight within German High Command, and for the most part, it was limited to special problems of evaluation.^[56]

The liaison also was limited to the field of evaluation. Owing to the location of the Chi-Stelle and personal acquaintances, especially with Luftwaffe Ic, it was considered excellent.^[56] Prior to the daily conference, any new problems and all the material that had come in the previous night, were discussed by telephone between the Referat and the operations office, Ic of the Luftwaffe. The discussions that took place included Allied air transport and the current air ferry situation reported by Referat B5 in Oberhaching.^[56]

When United States radio stations appeared on airfields in the Poltava area, as US bombers and fighters escort landed in these airfields, following attacks on Germany or Rumania, an evaluator from Referat C was dispatched to Referat D in Warsaw. A large intercept platoon was transferred to Warsaw to monitor this traffic.^[56] However, the results were insignificant and after fourth months the W/T platoon was recalled.^[57]

In 1944, the Referat places a liaison officer with Dulag Luft, that resulted in many pieces of collateral intelligence being collected, as well as important confirmation of previously gathered intelligence.^[57]

In the last months of the war, the Referat was merged with the evaluation company of Regiment South.

• "Volume 5 – The German Air Force Signal Intelligence Service" (PDF). TICOM. Retrieved 9 June 2017. This article incorporates text from this source, which is in the public domain.
• Seabourne, J.G. "IF-180 SEABOURNE Report:The Signal Intelligence Service of the German Luftwaffe – Volume V Chi-Stelle" (pdf). Google drive. Ninth Airforce. Retrieved 9 July 2017. This article incorporates text from this source, which is in the public domain.
• Seabourne, J.G. "IF-181 Seabourne Report, Vol. VI. "Origins of the Luftwaffe SIS and History of its Operations in the West. Part 1"" (pdf). Google drive. Ninth Airforce. Retrieved 4 August 2017. This article incorporates text from this source, which is in the public domain.
• Seabourne, J.G. "IF-181 Seabourne Report, Vol. VI. "Origins of the Luftwaffe SIS and History of its Operations in the West. Part 2"" (pdf). Google drive. Ninth Airforce. Retrieved 4 August 2017. This article incorporates text from this source, which is in the public domain.
• Seabourne, J.G. "IF-184 Seabourne Report, Vol. IX "History of Operations in the South Luftwaffe SIS"". Google drive. 9th Airforce. Retrieved 20 September 2019. This article incorporates text from this source, which is in the public domain.
• Seabourne, J.G. (24 November 1945). "IF-186 Seabourne Report, Vol. XI. "History of Operations in the East Luftwaffe SIS" (pdf). Google drive. Ninth Airforce. Retrieved 31 July 2018.
• Seabourne, J.G. (24 November 1945). "IF-187 Seabourne Report, Vol. XII. "Technical Operations in the East Luftwaffe SIS" (pdf). Google drive. Ninth Airforce. Retrieved 31 July 2018.
• "I-13 Composite Report on Two Interrogations of Oberstlt. Rudolf Friedrich, Chief of the G.A.F. Sigint Service, 18/5/45 and 9/6/45". Google drive. TICOM. 6 June 1945. Retrieved 24 November 2017. This article incorporates text from this source, which is in the public domain.