[Bruce Dennis]

SECRET A. D. I. (K) Report No. 357/1945.
THE FOLLOWING INFORMATION HAS BEEN OBTAINED FROM P/W. AS THE
STATEMENTS MADE HAVE NOT AS YET BEEN VERIFIED, NO MENTION OF THEM.
SHOULD BE MADE IN INTELLIGENCE SUMMARIES OF COMMANDS OR LOWER FORMATIONS, NOR SHOULD THEY BE ACCEPTED AS FACTS UNTIL COMMENTED ON IN AIR MINISTRY INTELLIGENCE SUMMARIES OR SPECIAL COMMUNICATIONS.

RADIO AND RADAR EQUIPMENT IN THE LUFTWAFFE - II
Navigational Aids.
1. This report is the second of the series dealing with radio and radar equipment in the Luftwaffe.
2. As in the case of the first of the series (A.D.I.(K) 343/1945) dealing with Blind Landing and Airborne Communications Equipment, it is based on interrogation of General Nachrichtenführer MARTINI, Director General of G.A.F. Signals, and a few important members of his staff, and has been supported by a file of current papers which were in the possession of the General’s Chief of Staff.
3. An index of the numerical designations of the navigational equipment mentioned in this report appears in Appendix I.
4. For convenient reference, a translation of the document entitled "Funkausrüstung der Flugzeugmuster, Notprogramm" (signal Equipment in the G.A.F. - Emergency Program) - item 45/99 ff in A.D.I.(K) Documents List 45/9 - which has also appeared as an Appendix to A.D.I.(K) 343/1945, is reproduced as Appendix II to the present report but the list of equipment contained in that document has been omitted as Appendix I gives a fuller list.

TRENDS OF DEVELOPMENT.
5. Throughout the course of the war, the general standard of German navigational training was undoubtedly inferior to that of the Allies. A simple form of navigation was taught but navigators track plotted only and relied on W/T aids and in particular positioning by means of loop fixes as the main basis for their navigation.
6. During the early part of the war extensive use was made of Knickebein and other beam systems, but later this form of navigational aid gave way to the "Y" control system (better known by the Allied codeword Benito) and "Egon".
7. Sonne was universally accepted as an outstanding success and from the time of its inception in 1942 research was continuously directed towards overcoming its imperfection, in particular the range limitation. Komet was a typical example, of attempted improvement on these lines
8. The Germans were patently backward in the field of pulse systems and the majority - if not all - of their navigational aids of this type were copied from Allied methods.
9. The fear of the Allied countermeasures was much to the fore during the last two years and considerable research and efforts was devoted to offsetting such interference and to perfecting systems which would reduce and if possible preclude the danger of jamming. Another factor always present in the minds of those responsible for tactical navigational requirements was that the apparatus must be as light and small as possible because of the limited space available in German aircraft.
10. During the last stages of the war, and as a natural consequence of German air policy, being forced to concentrate on the defensive, thereby involving almost exclusive use of fighter power, a great deal of attention was devoted to the development of simple navigational aids suitable
for single-engine aircraft of which Rübezahl was a typical example.

D/F LOOP EQUIPMENT.
PeGe (Peil Gerät) 6.
11. PeGe 6 was the successor of PeGe 5, the standard loop D/F, set in use at the beginning of the war, and. operated on 150 - 1200 kc/s (2000-250 meters). It provided automatic D/F facilities, the W/T operator merely having to tune to the signal and the "answer" being produced on a course indicator.
12. In the opinion of P/W, who was responsible for operational requirements in the navigational field and who had had fairly extensive navigational experience with K.G.40, PeGe 6 was less reliable than the manually-operated PeGe 5 as the automatic D/F facilities could not distinguish between the true signal and jamming and were apt to record bearing midway between the two if they were near together. The human ear was much more acute and could distinguish the minimum of the real signal from that of the "phoney” one. It had the further disadvantage that it was a heavier piece of equipment than the manually operated set.

FuGe 141
13. The FuGe 141 operating on a frequency band of 58.0 - 59.2 mc/s was a receiver with a D/F loop fitted to Air Rescue aircraft used for homing on to the NS 4 emergency radio set carried on the chest by pilots.
14. The NS 4 had a flexible steel tape aerial and batteries which gave it an endurance of 2 to 2,5 hours.

FuGe 142.
15. The FuGe 142 using the 2000 - 250 metre band was a small D/F battery set for use in emergency in the event of failure of the aircraft' s electricity supply.
16. The FuGe 142 had a manually-operated loop and its accuracy was only 10° to 15°.
17. When the P/W who, in October 1944, took over the navigational tactical requirements first made its acquaintance, he discovered that the designer of the emergency set, while having the laudable object of assisting a crew in dire emergency when they where probably well and truly lost, had omitted to include any sensing arrangement. The set was, therefore, quickly scrapped as being as much of a danger as an aid.

FuGe 145
18. The FuGe 145 was a simple type of D/F set in development for use in single-seater aircraft. It was for use with M/F beacons and was designed for use by coastal reconnaissance aircraft, as for example the Do.335, so that they could obtain a bearing when flying at low level.
19. It was much lighter than the PeGe 6 and had no automatic facilities, but was very easy to operate. P/W had thought that it might ultimately supersede the PeGe 6 for other types of aircraft.

Suggested loop for fighter aircraft
20. The research centre at Rechlin had been asked to examine a rough type of loop for singleseater fighter aircraft, which would consist of a loop built into the pilot' s helmet. It was thought that this would enable the pilot to establish the general direction of a beacon by movements of
his head and without recourse to the use of a compass.
21. This idea was tried out and seemed promising, but was never fully developed.

HOMING BEACONS.
Schwanboje.
22. The Schwanboje was a waterborne V.H.F. beacon dropped by parachute and originally used by K.G.40 for marking convoys or submarines. In the autumn of 1944 a 1ine of Schwan buoys was used to aid the He.111's when launching V-1’s from the North Sea against this
country.
23. The beacon consisted of a frame aerial and transmitted on a wavelength which could be homed on by the FuGe 17, the standard equipment of K.G.40 in 1942 when the Schwanboje came into use.
24. The set was powered by accumulators and had a live of five hours; by the means of a clockwork device it could be pre-set before release so that it ran for a testing period immediately on release and later started up again after a prescribed interval governed by the expected time of arrival of the homing aircraft. The buoy was fitted with a self-destroying
charge operated automatically.
25. A later type of Schwanboje operated on the 38 - 42 mc/s waveband so that aircraft equipped with the FuGe 162 could also use the system.
Biene
26. Biene is the code word for a responder beacon. The idea of responder beacons for homing purposes had only been hit on in 1944 and Bienen to respond to the different airborne radar sets were still under development in 1945. The FuGe 243 - Hohentwiel Biene – had been used by coastal units in Norway, in February or March 1945.
27. Responder beacons were also being developed for use in the Baldur method of navigation (see paragraphs 79, 82 of this report).

BEAM SYSTEMS.
Zyklop.
28. This was the latest form of the well-known Knickebein working on 30 - 33,3 mc/s and received by E.B.L.3 in the aircraft. It was a mobile station which could be fully erected into operation within a week.
29. A still more mobile unit known as the Bock-Zyklop had been introduced. This could be set up in three days and could be adapted for use on the FuGe 16 frequency although as yet, according to documents, no visual indicator for the FuGe 16 had been developed.
30. The 120 W ground transmitter was called the ???? which gave a beam 0.5° wide and a range of 300 km. at a height of 5,000 meters. The Zyklop systems had been made use of on the Russian front up to the end of the hostilities.

Sonne.
31. The Sonne beacon system which worked on a frequency of 270 - 480 kc/s was received in the aircraft on the FuGe 10. It was considered an extremely effective daylight system but the range limitation was a disadvantage. Fixes could be obtained from ranges up to 1,000 - 1,200
km. Sonne 6 at Quimper which was the most efficient of the Sonne beacons, had been used on an occasion at a distance of 1,400 km.
32. The sectors served by Sonne covered, an angle of 120 – 150°. The beacon was very reliable over the centre sector of 100°, but the error increased progressively towards the edges of the beam in conformity with the sine law.
33. At night errors up to 4° were liable to occur even in the centre of the sector of the beacon and no real use could be made of it.

Mond.
34. To improve the Sonne beacons both in range, and accuracy, an experimental system working on the same principle, but on 3000/6000 kc/s was tried out in 1942. The shorter wave transmission did not prove very reliable and was given up about the end of 1943.

Stern.
35. Finally a beacon of the Sonne type under the name "Stern" was designed for use on a V.H. frequency. It, not unnaturally, only gave optical range and was, therefore, of no practical value and was not developed.

Dora.
36. One P/W had seen documentary mention of Dora which he believed was a navigational aid system and a precursor of Komet. He did not know whether it worked on the same principle but the Komet experimental site at Kolby was on the former Dora site.

Komet.
37. In 1942 the question of navigation over the Atlantic stood in the limelight . As the He 177 was supposed to be coming into service shortly to enable K.G.40 to reach further West, the need for navigational equipment of longer range became acute.
38. A year or so earlier Professor von HANDEL had categorically stated in a lecture that a long-range navigational system based on pulse would inevitably be extremely inaccurate. In view of Professor von HANDEL's views on pulse systems, an improved form of Sonne which would give much greater ranges and be less susceptible to night effect was given high
priority.
39. The system evolved was called "Komet" and experimental stations were erected at Bordeaux and Kolby (see A.D.I.(K) 364/1944). The ground station called for an array of no less than 127 masts and 19 control huts in order to cover a 90° sector. It worked admirably provided a 10° sector only was covered, but as soon as the planned 90° sector was put into operation, mutual interference between the masts arose and the various lobes radiated were no longer of symmetrical pattern, with the result that large errors crept in.
40. Research on this delayed the project considerably. After the invasion when long distance reconnaissance in the Atlantic was no longer practical politics, the Komet system was given up without ever having been effectively used. The development people were the more pleased to dispense with it since it left the German radio research and industry free to deal with other more urgent matters.
41. The beacon was to operate on frequencies of 5000, 9000 or 12,000 kc/s received on the FuGe 10K, and it was estimated that ranges up to 3000 km would be obtained. The system employed was to be similar to that used in the Sonne but instead of obtaining one reading per minute, oscillation of the beam was to be speeded up to give 100 readings par minute.
42. The true bearing of the aircraft was automatically recorded by the FuGe 124 which was known as the Kometschreiber. The recording took the form of a series of vertical lines, one for each reading, printed on a strip of paper. At the same time as the lines were printed the Kometschreiber recorded the section of the swept area in which the aircraft was flying, thus giving what amounted to a rough position.
43. The fine reading was obtained from the length of the recorded lines. Any inaccuracies due to night effect could be easily eliminated by averaging the length of the lines, as recorded, on the paper strip, by eye.
Erika.
44. Erika was a navigation system (see A.D.I.(K) 364 and 409/1944.) which had already reached the development stage in 1942 but its operational employment was of brief duration and it was soon discarded in favour of Bernhard.
45. Erika was based on the principle of a V.H.F. (30 - 33 mc/s) beam oscillating rapidly over a segment of about 60 – 90°. The beam was phased, a different phase being picked up in different sections of the segment and read off in relation to a standard phase producer in the aircraft. In order to obtain a fix, two such Erika stations had to be received and to receive each station no less than two E.B.L.3's were necessary making a total of four receivers.
46. The range presentation unit in the aircraft, FuGe 121, took the form of a clock-face with a needle indicator and calibrated, P/W thought, from 0 -100. A specially prepared map was required to establish bearing.
47. A disadvantage of Erika was the vulnerability to jamming, interference signals modifying the phase and thereby giving inaccurate readings. The great weight, carried and the bulk of the four receivers, which were particularly cumbersome in the relatively small aircraft in use in the G.A.F. made its widespread use impracticable.


Bernhardine.
48. This system was first introduced in 1942 for use by bomber aircraft, but was later dropped in favour of the Benito and Egon control systems. With the increasing British jamming during night raids it was reintroduced for use in night fighter commentary (see A.D.I.(K) 125/1945, paras.5 to 29), which it was thought could only be jammed with great difficulty.
49. The term “Bernhard” was used for the ground stations whilst the airborne recording equipment was called Bernhardine or FuGe 120. The latter made use of the E.B.L.3. receiver as the transmissions lay in the 30-33 mc/s band.
50. At the time of the German capitulation, the following three transmitting stations were in operation, the first two, of which could transmit commentary.-
-Thisted, on N.W. coast of Denmark.
-Bretstedt, N. of Husum, Germany.
-Trebbin, S.E. of Berlin.
51. A further station near Breslau had been almost completed when it had to be dismantled on account of the Russian advance. Additional stations were in the course of construction near Kassel, Munich, Pilsen and Vienna.
52. The Bernhardine system was looked upon as a considerable improvement on Erika. It gave 360° coverage as compared to 60/90° with Erika and, whereas from the jamming aspect stray signals could disturb the phase of Erika causing false indication, in the case of Bernhardine,
interference merely resulted in no reading being possible, and furthermore to attain this through 360° a very powerful jamming transmitter flying near the ground station would be needed.
53. The Bernhardine system was not regarded as unjammable but it was thought that use of high power and aerial gain would render jamming by airborne means impracticable.
54. In addition to the E.B.L.3 receiver, the airborne Hellschreiber FuGe 120, also called the Bernhardine, which gave both bearing and commentary was employed. According to P/W the FuGe 120 was large and weighty and the first improvement aimed at was to reduce the weight and provide a set which occupied less space in the aircraft. To this end an attempt was made to eliminate the use of paper strip for the Hellschreiber and a rotating "Folienschreiber" a cellophane paper moving over a sticky carbon surface which constituted a self-eraser - was employed. This projected recording method proved a failure and the use of paper strip had to be reverted to. According to documents the type using paper strip was known as FuGe 120a, and the self-erasing recorder FuGe 120b.
55. A smaller model, the FuGe 120k, to operate on the paper strip principle which constituted the latest improvement, was still in the development stage at the conclusion of hostilities. Previously the ground transmitter broadcast simultaneously from the upper and lower aerial
arrays on two frequencies close enough to one another for them both to be received on one channel of the E.B.L.3. One lobe was used for coarse D/F, the other for fine. The two frequencies were then separated by a filter before being fed into the Hellschreiber. The FuGe 120k was designed for use with a ground transmitter operating only on the coarse D/F frequency. The filter could therefore be dispensed with and considerable weight saved in the airborne set at the expense of some accuracy in D/F.
56. With the loss of D/F accuracy the sharp “V” in the vertical printing indicating the reading (see diagram A.D.I.(K) 125/1945 para.18) became a gap about 4° wide. To facilitate the reading of the centre of the gap by eye, and to reduce the size and weight of the apparatus, the vertical lines referred to above were superimposed on the scale which could then only be read in the gap. This allowed the paper strip to be considerably narrower.
57. The FuGe 120k was designed primarily for use in single seat jet aircraft but was also to be embodied in the Ju.88 where space was at a premium, as soon as sufficient numbers of this set were available.

Hermine.
58. The Hermine system was originally developed, in response to a tactical requirement formulated during the second part of 1942, as a navigational aid for the purpose of giving an approximate bearing to single-engine night fighters engaged on “Wilde Sau” operations.
59. By the time the initial difficulties in development had been overcome Wilde Sau night fighting had almost ceased; it was found however that Hermine could be used to advantage by day fighters, and it came into operational use.
60. An accuracy of ±5° was assumed, but it was found in practice that this could be improved upon to ±3° by experienced pilots.
61. Thirteen or fourteen ground stations were in operation by Easter 1945 which, P/W claimed, gave complete coverage of the Reich. It was intended to fit two Schlechtwetter (bad weather) Fighter Geschwader with the necessary airborne equipment, and this program had been onethird
completed by May 1945. One P/W had heard that ten to fifteen Me.262's of K.G.51 were amongst the aircraft so equipped.
62. The following may be added in modification of the description of the Hermine system given in A.D.I.(K) 125/1945, paras.59 to 62. The Hermine rotating beacon transmits a continuous tone on which is superimposed a speaking clock which counts from 1 to 35, each
figure representing tens of degree. Over an angle of about 15° the continuous tone falls to a minimum and rises again. During this period the voice appears to become more audible and the pilot can estimate where the minimum of continuous tone occurs, and so obtain his bearing from the beacon.
63. The beacon recognition is given by means of a self-evident code name for example, "Berolina” for Berlin – which is spoken by the voice in place of 000°.
64. The airborne equipment is the FuGe 125 consisting of the E.B.L.3 with the Tzg (Telephoniezusatzgerät) which enables the 30.0 - 33.3 mc/s transmission picked up on the E.B.L.3 receiver to be heard in the pilot's headphones. Though the Hermine beacons were fully operational there was a scarcity of FuGe 125 sets, as a result of which practical experience of this system was too limited to judge of its efficiency or to lead to further improved tactical requirements been formulated.

PULSE SYSTEM.
Ingolstadt
65. All the P/W had heard reference to Ingolstadt and agreed that it was a long-range navigational system.
66. One P/W thought that Ingolstadt was the cover name for a pulse navigation system using hyperbolic curves and similar to British Gee; it was originated by Telefunken in 1938 but was then turned down by the R.L.M. In his recollection the original Telefunken idea derived from
theoretical discussions at an international conference before the war.
67. As mentioned earlier under the heading of Komet, Professor von HANDEL maintained that owing to the incidence of mutual interference between direct and reflected waves the system was impracticable at long range. In consequence of von HANDEL’s view the system was dropped.
68. Much consternation and annoyance was occasioned in 1944, when it was found that the Allies were successfully operating a similar system.
69. Truhe is the cover name used to describe navigational aid system, using ground stations, similar to those of British Gee. In effect the British Gee stations were also used, the airborne sets being almost identical with the British Gee boxes.

Truhe.
70. There is no very distinct difference between "Truhe" and "Hyperbel". The latter term was originally coined to denote our Gee. It was also used when German aircraft equipped with British Gee sets made use of British ground stations.
71. The British Gee chain was used successfully but it was realised that so soon as the Germans lost an aircraft, over England, a change would be made. The German "Y" service monitored the British ground stations to follow any change in Gee phasing and passed advice of such change to their aircraft by W/T.
72. Truhe referred to the German system which was ultimately to cover the 20 to 100 mc/s band and employed various types of ground transmitters including Feuerhilfe, Feuerstein, Feuerzange and Feuerland. All these transmitters could also be used to jam our own Gee, further details of which will appear in a subsequent report on German Radio Countermeasures.
The original 46 to 50 mc/s system was known as Truhe I and the new 30 to 60 mc/s system as Truhe II.
73. A chain of Truhe stations was built around Berlin, primarily for training purposes and there were in addition groups of ground stations in the Schwarzwald and in Pomerania. The last named was intended for operations against Russia and it is not known if the stations were
destroyed before their capture.
74. The airborne sets which were known as FuGe 122 covering 46-50 mc/s and FuGe 123 covering 25-75 mc/s were replicas of the British Gee boxes and according to P/W were equivalent to British R.1324 and R.1355. These German sets were slightly smaller and more compact than the British sets.
75. Truhe was used by F.A.G.2 and K.G.66, but up to the time of capitulation only a few FuGe 122 and FuGe 123 sets had been produced and only one R.F. box for the latter set.

Baldur.
76. The Baldur range-measuring system is comparable to the British G.H. and appears to have been imitated from it. It was referred to by P/W as “Egon in reverse" and was the only navigational system developed by the German by means of which an aircraft could measure distance from a known source as opposed to fixing itself by a position line. As the G.A.F. staff were still thinking in terms of a grandiose bomber policy as late as June 1944, it was intended for use by bomber aircraft for pinpointing targets and for accurate blind bombing.
77. The wavelength employed was in the neighbourhood of 2-4 meters and fell in the SN 2 band.
78. Only two experimental transmitters, both located in Lower Silesia, were erected and one P/W maintained that this system never progressed beyond experimental trials by the manufacturers. It was eventually relegated to low priority owing to the virtual cessation of German bomber operations and the pressure of more urgent demands on radio research and the radio industry.
79. The airborne equipment was known as the FuGe 126 which was made up of a transmitter to interrogate a ground responder beacon, a receiver and a presentation unit. The receiver and transmitter were SN 2 units, though P/W thought they might have been slightly modified for use with Baldur.
80. From documents, the presentation unit appears to have been a modification of the Würzburg range measurement tube, and the accuracy is given as ± 100 meters at all ranges, but this was thought to be purely theoretical and P/W doubted whether it would have been possible to achieve this accuracy in actual practice.
81. A smaller airborne set, the FuGe 126k (k = klein = small) was built for use by single-seat aircraft. In reducing the size and weight of the set, and making it pilot-operated, accuracy had to be sacrificed. P/W, who was responsible for putting up the tactical requirements, considered a clock-face presentation to be the ideal solution. It was expected that the accuracy of the FuGe 126k would then be of the order of 500 meters independent of range.

Baldur - Truhe
82. It was planned to experiment on a combination of Baldur and Truhe (Gee) for use by bombers. The intention was to use a hyperbolic grid line of Truhe for the target approach. This could be pre-set, and the pilot could fly along it by keeping the blip centralised, and could ascertain his exact position along the line by measuring his distance from a Baldur beacon. This system was considered simpler particularly for a single-seater aircraft, than the method of using two hyperbolic grid lines or two distances from Baldur beacons. The first experimental sets were to be ready in the autumn of this year.

Baldur - Bernhardine
83. A further project was a combination of Baldur and Bernhardine to give simultaneous bearing and range. The range indication was to be obtained by the pilot pressing a knob when the range would appear in kilometres on a dial. This system was suggested for use by both day fighters and bombers.

GROUND CONTROL SYSTEMS,
Benito.
84. The Benito system of control using FuGe 16, known to the Germans as "Y", is too well known to warrant description. The following paragraphs deal with recent developments.
85. When operating the bomber Benito procedure with the narrow beam. (0.3°) essential for azimuth accuracy, it was easy for the bomber pilot to get on to one of the side lobes in error since these were only about 3° from the main beam.
86. In order to minimise the possibility of mistake and to relieve the pilot of the strain of flying on a beam, an automatic device, the FuGe 28a, was in use which was the improved and final form of the old Y-Gerät of 1941. Documents dated about June 1944 show that it was used in conjunction with FuGe 17, but P/W thought that it had been modified for use with FuGe 16ZY as well.
87. The procedure was that the bomber pilot flew on instructions conveyed over the FuGe 17 until it had been established by ground D/F stations that he was on the true beam, when the code word "Bako" would be given whereupon the pilot would switch on the FuGe 28a which took over control of the automatic pilot and kept him on the beam.
88. P/W gave the accuracy of range measurement with the Bomber Benito procedure as only ± 1 km. at maximum range.

Egon.
89. The original Egon procedure which involved the use of two Freyas, the one for rough positioning and the other for fine positioning - later became known as "Egon Einstand" (One location) to differentiate from an improved system termed “Egon Zweistand” 90. Egon Zweistand was evolved to offset the inaccuracies in azimuth D/F, and cash in on the range accuracy of radar. With Zweistand a third Freya was introduced, placed some
considerable distance from the other two Freyas in order to give a distance cut. It was intended for use by bomber aircraft operating over England or on long range sea missions.
91. The original Zweistand system, which was first tried out in Italy by a Schlacht unit, was somewhat primitive in that the readings from the extra Freya were telephoned through to the plotting centre and worked out before being plotted on the Seeburg table.
92. To eliminate the delay thereby involved a landline connection was introduced to feed the Freya pulse to the C.R.T., which then had two blips showing ranges from the two Freya sites.
The vulnerability of landline to disturbance and destruction later led to the development of a W/T transmitter and this method was employed successfully in operations.
93. Since the Freya pulse was not strong enough to trigger off the FuGe 25A at ranges exceeding 250 kilometres, it was planned to supplant the Freya by extra powerful Wassermanns, and thereby increase the effective range of Egon Zweistand to 350 kilometres.
94. A further line of development was the provision of a new type of control table giving the exactitude of plotting necessary for pinpoint bombing. This control table, which was under development at Rechlin, made use of complicated mechanical apparatus for accurate projection
of the position of the bomber. One of these tables was destroyed in the course of a daylight air attack on Rechlin in February 1945; two other tables were in existence at the time of the capitulation, and were located somewhere in Western Germany.
95. Egon when first introduced was received with some scepticism by the crews, as it was felt that it was too vulnerable to jamming. After it had been used operationally without being jammed in the attacks on London in March 1944, the procedure was adopted with greater confidence, and it gained a good reputation. As recounted in A.D.I.(K) 343/1945, Egon was
always favoured by the R.L.M. technical development section in preference to Benito control.
96. A drawback of the system was its restricted range at low altitude, which according to P/W was the reason why it was not used in conjunction with V.1 operations.

Nachtlicht
97. The Nachtlicht system was the first method of control not using R/T speech to be improvised by the Germans, and had been tried out during the raids on London in the spring of 1944.
98. It had been observed that the red signal lamp of the FuGe 25A was illuminated when the aircraft was being swept by a Freya, and it was suggested that use could be made of this as a means of transmitting morse signals from the ground. A Freya operating on a special wavelength, which P/W thought was 2.55 meters, was set up on the Channel coast and was used to send simple instructions to the aircraft attacking London by means of visual morse indications on the lamp of the


FuGe 25A.
99. The primitive method of giving distant control indications was the forerunner of "Nachtfee", "Barbara" and "Barbarossa".
100. Luftkurier was the first development of the Nachtlicht idea. It was primitive device intended to give visual indication to the pilot by means of a pointer which was started and stopped by the reception of pulses.
101. P/W thought that Luftkurier was first tried out by K.G.66 on the Freya band, but it was so easy to jam by the addition of extra pulses that it was never developed.

Nachtfee
102. Nachtfee was the term used to describe a system for the transmission of control instructions to a pilot in the beam of the controlling Freya through the medium of a C.R.T. indicator similar to the Lichtenstein range tube. The airborne equipment used was known as FuGe 136 and weighed 12 kg.
103. The original purpose of Nachtfee was, to provide a solution to the jamming of R/T control systems, and it had been used operationally by the Pathfinders of K.G.66 for mines in the Scheldt estuary. It was to be adapted for use by night fighters to overcome our jamming of the
night fighter commentary.
104. Nachtfee was a system using the FuGe 25A as receiver.
105. The presentation screen in the aircraft was inscribed with various commands both on the inside and outside of a circular time trace. There was a stationary zero blip in the 12 o'clock position, and when an instruction was radiated the pulses received caused a second blip to emerge from the first and travel round the C.R. tube in a clock-wise direction, presumably by a slight change in p.r.f. This blip came to a stop and the command corresponding to its position could be read off on the inside of the time trace where a total of about eight different instructions were inscribed. It took from one to two second, for the blip to travel round the tube.
106. It was thought that the further eight commands inscribed on the outside of the time trace were denoted by the blip making a complete circle starting round a second time before coming to rest at any one of the eight sectors. In this way a total of sixteen different orders could be given. For night fighters such instructions as "turn left/right", "climb", "dive”, etc. appeared on the inner side and figures for transmitting bearing on the outer side of the trace.
107. This system was used operationally, but it was found that, apart from the susceptibility to jamming, other pulse transmissions could interfere by unlocking the system and thereby cause wrong positioning of the indicator blip.
108. Another pronounced objection to the Nachtfee lay in the fact that it was necessary for a member of the crew to watch the C.R.T. indicator uninterruptedly for missing one blip indication might give the message a false value. It was not therefore possible to use it in singleseater aircraft.

Barbara
109. This apparatus, also called FuGe 138, consisted of an attachment to the FuGe 25A receiver and only weighed 2 kg. This unit contained an audio filter which allowed the pilot to hear morse signals superimposed on the Freya interrogator transmission if they were emitted on a suitable audio frequency usually about 800 cycles. By keying other morse signals on different audio frequencies and equipping aircraft with suitable filters, more than one aircraft could be controlled by a single Freya.
110. Barbara was to be used for Egon control of ground-strafing aircraft and bombers but not for night fighters.
111. In the Germans' opinion there were three disadvantages, namely that the Allies could intercept and make use of signals so transmitted, that the aircraft had to be in the beam of the Freya if it were to receive, and so an aircraft "lost" by the Freya owing to jamming could not be communicated with and finally that, though intended for single-engined aircraft, fighter pilots rarely had sufficient command of morse to be able to use this type of control.

Barbarossa
112. Barbarossa was a set designed to meet the same requirements as Barbara but to remedy two of the drawback mentioned in the last paragraph.
113. The instructions to the aircraft were to be transmitted by code pulse modulations which were passed through a "pulse filter" in the airborne set and a written indication obtained on a Hellschreiber. The pulse filter and Hellschreiber unit were attachments to the FuGe 25A and were known as the FuGe 139. This apparatus was in development at Rechlin under the
supervision of Stabs.Ing. von HAUTEVILLE.
114. With this arrangement pulse modulations could not be read by the Allies, and for spoof purposes in order to produce a wrong indication we would have had to know the exact type of modulation accepted by it. Visual indication was also quicker and did not depend on knowledge
of morse.
115. This scheme was only in a very early stage of development and P/W were unable to give details. It was hoped that in due course it would be possible to develop matters a stage further and find a means of transmitting scrambled speech instead of morse, but P/W understood that
the question of pulse modulation for speech transmission had not been solved.

Rübezahl
116. Consideration had been given in 1945 to the introduction of a crude system of navigation which could be only used within the boundaries of the Reich. This was to go under the code name of Rübezahl, and the fact that it was seriously considered and actively supported by the P/W responsible for Navigational Aids on the G.A.F. signals staff is an interesting reflection of the depths to which a combination of Allied jamming under-trained fighter had forced German technique.
117. It was expected that in the course of the summer of 1945 thousands of 162 Volksjäger would be available for the protection of the Fatherland. They were to be equipped with FuGe 24, which was to become the standard G.A.F. R/T set as described in A.D.I.(K) 343/1945. This set did not for the present give Benito control facilities and indeed as they were
short-range, high speed, fair-weather aircraft it was not certain that Benito control would be essentially needed.
118. It was essential that their relatively inexperienced pilots should have a simple means by which they could locate their approximate position without any additional navigation equipment having either to be manufactured or carried in the aircraft. It was therefore decided
to develop a system which could be used with FuGe 24.
119. In order to direct the Volksjäger pilots to their target, recourse was to be had to the night fighter system of broadcasting a commentary, and this commentary was to be combined with the primitive navigation system Rübezahl.
120. It was therefore planned to set up ground transmitters over Germany at 30 km intervals. The transmitters were to be beamed upwards, so that at 6,000 meters the polar diagram was about 40 km in diameter and lobes from neighbouring transmitters just overlapped, thus covering the whole area. Each transmitter emitted a plain language recognition signal in the
form of the name of its district, e.g. Halle, Magdeburg, etc.
121. All transmitters were to be operated on the same frequency so that to locate himself the pilot merely tuned his FuGe 24 to the frequency for the day. The ground transmitters were to be adapted from the FuGe 15 transmitters which had been manufactured in quantity as described
in paras. 23-39 of A.D.I.(K) 343/1945 before it was found that the FuGe 15 was unsuitable as an airborne R/T set. They were renamed Bs.15 (Bodensender).
122. Later it was believed that the night fighters which were also to carry FuGe 24 (see appendix 1) would also use the Rübezahl commentary as yet another alternative source for vectoring themselves to the bomber stream.