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Old 30th October 2018, 10:50
Bruce Dennis Bruce Dennis is offline
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Kg40 in item 37

"SECRET A. D. I. (K) Report No. 357/1945.
Navigational Aids.
1. This report is the second of the series dealing with radio and radar equipment in the
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.
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.
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
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.
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
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.
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).
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.
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.
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.
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.
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.
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
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.
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.
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.
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.
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
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.
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.
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
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.
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.
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.
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
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.
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
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
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.
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.
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
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."

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