Researching the Luftwaffe through Prisoner Interrogations

[Bruce Dennis]

"SECRET A. D. I. (K) Report No. 380/1945
THE FOLLOWING INFORMATION HAS BEEN OBTAINED FROM P/W
AS THE STATEMENTS 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 UNTIL COMMENTED ON AIR MINISTRY
INTELLIGENCE SUMMARIES OR SPECIAL COMMUNICATIONS.

RADIO AND RADAR EQUIPMENT IN THE LUFTWAFFE – IX.

German Radio Countermeasures.
1. This report is the ninth of the series dealing with
radio and radar equipment in the Luftwaffe. The present
information was mainly obtained from Dr. Ingenieur SCHOLZ, a
civilian employee of the Reichspost Zentrale who was in
charge of a sub-section of Abteilung 6 of the
Generalnachrichtenführer dealing with the problem of RCM
(radio countermeasures).
2. Interrogation of this man has been supported by
information gained from other members of General MARTINI's
staff and by a number of relevant documents of recent date in
possession of the General's Chief of Staff. Some useful
additional help was given by two engineers who had recently
been engaged in testing ground and airborne jamming equipment
at the G.A.F. research establishment at Werneuchen.
3. The radio countermeasures used by the Germans have been
treated in this report under four headings, the first being a
brief historical account of their employment, and the other
three dealing in turn with RCM against communications, metric
radar and centimetre radar. The types of jamming transmitters
referred to by name, or of which a mention has been found in
documents, are listed in alphabetical order and their
functions briefly described in Appendix I to this report.

THE GERMAN MONITORING SERVICE AND EVOLUTION OF COUNTERMEASURES.
BASIS FOR COUNTERMEASURES.
4. At the beginning of the war the G.A.F. High Command was
not radio minded; GOERING in particular has been frequently
accused by his underlings of paying no attention to technical
matters. In the opinion of General MARTINI's staff, the vital
importance of radio warfare and radio countermeasures was
only truly appreciated by the General Staff towards the end
of 1944. Those responsible for German jamming, therefore, had
great difficulty in obtaining permission to use the
countermeasures to the extent that they could have wished.
5. The countermeasure organisation relied in the first
place on the German "Y" service, which formed Abteilung 3 of
General MARTINI's staff, to give advance information of new
radio activities, and for this purpose it employed a staff of
expert radio engineers whose task was to identify and explain
any new frequencies or types of transmissions received. If,
however, novel features in a monitored transmission were
observed and could not be explained, a commission for the
investigation of the particular subject was set up. This
commission was composed of representatives of the "Y" service
and of the Development (E) departments of the R.L.M.,
representatives of the research (F) department of the R.L.M.,
and such experts from the leading firms as had special
experience in the field of radio which was thought to be in
question.
6. Evidence collected by listening, though it could be very
valuable as intelligence, did not necessarily tell the whole
story or indicate the most suitable form of countermeasures.
As far as airborne equipment was concerned, statements made
by prisoners of war often helped to fill out the details and
the capture of equipment and its identification with the new
transmission was of great value, even if the equipment was
severely damaged.
7. Intelligence information from the above three sources
could usually be pieced together to tell the whole story, so
that decisions could be taken as to whether radio
countermeasures were required.
8. The Germans relied very largely on the laboratories and
experience of the Reichspost Zentrale (RPZ) to solve the
technical problem of how and with what equipment to jam, and
they obtained for the duration of the war the loan of an
engineer of that organisation (the present P/W) who was put in
charge of RCM and carried out liaison with RPZ to this end.

EVOLUTION OF COUNTERMEASURES.
9. The decision to jam a particular type of transmission
rested very largely with General MARTINI and was often taken
despite the protests of the "Y" service section of his staff,
who were interested professionally in monitoring all
transmissions. Particularly in the case of R/T, the "Y"
service insisted that more strategic and tactical information
could be obtained by D/F’ing enemy transmissions than any
tactical advantage which might be gained by jamming them.
10. As an instance of the extent to which the decision lay
with General MARTINI the following case was quoted: In 1942
Allied night fighters were becoming a nuisance in the
Mediterranean area but General KESSELRING had to ask General
MARTINI’s permission to jam their ground-to-air R/T control in
his theatre of operations and only then could the
countermeasures be undertaken.
11. The first German radio countermeasures were instituted in
September 1940 during the day bombing raids of the Battle of
Britain and were directed against British radar operations in
the Channel. The first and most important site used was that
at Mont Couple behind Calais were, by the end of the war, a
battery of some 35 jammers had been set up.
12. Radio countermeasures against Gee were put in hand in the
summer of 1942 and at about this same time the first attempts
were made to jam A.S.V. in the Channel. From this time on, the
countermeasure warfare increased and consideration was given
to jamming all types of new radar devices.
13. In about 1943 it was realised that countermeasures might
well be called for on every wavelength, and Dr. SCHOLZ put up
a requirement to the Reichspost Zentrale (RPZ) laboratories
for a series of jammers to be designed for covering all
wavelengths from 50 cm. upwards. These jamming transmitters
were designed in the Potsdam RPZ laboratories, and
improvements were constantly being incorporated in them so
that if there was a sudden call for countermeasures on an as
yet unused frequency, a practical design was available and
apparatus could be built at short notice.
14. As a result of this policy new countermeasures could be
put in hands quickly, but in practice they usually took
considerably longer to organise than might theoretically be
expected because the ground crews had to be trained in their
use. Dr. SCHOLZ stated that with a few exceptions these ground
crews were of second-rate material and it was frequently a
matter of weeks before they were sufficiently well-trained for
the countermeasures to become effective.

COUNTERMEASURES AGAINST COMMUNICATIONS.
GROUND-TO-GROUND COMMUNICATIONS.
15. With the possible exception of communications between land
and convoys, P/W believed that no attempt was made to jam
Allied W/T communications on the ground. Listening to them was
considered to be of the greatest strategic intelligence value
and little or no tactical object was served by jamming.
16. Radio countermeasures against the B.B.C. news service were
in the hands of civilian authorities, and the G.A.F. had
nothing whatsoever to do with them. Dr. MEINEL of the
Reichspost was believed to have been responsible for the
production of the type of jamming modulation which was
generally used.

GROUND-TO-AIR R/T.
17. The question of jamming Allied ground-to-air and air-toair
R/T was one of the points most strongly disputed between
the "Y"-service and the operational side of the G.A.F. The
"Y"-service maintained that by listening to and D/F’ing
traffic, both strategic and tactical intelligence was obtained
and that it was frequently their best source of early warning
of attack by aircraft; as a result relatively few attempts
were made to jam Allied R/T.
18. In the case of German raids on England the signals staff
agreed that there was an advantage in jamming British R/T
communications; this point arose when the possibilities of
Mark IV A.I. were first realised early in 1941. The question
of how to undertake countermeasures against British A.I. was
discussed and the weak point of the system was held to be the
R/T link from ground to air, because it appeared to be
essential for the night fighter to be brought within
2 km. of the bomber before contact could be made.
19. The Reichspost Zentrale built an airborne R/T jammer set
which was given the name of Karuso and was intended to prevent
R/T being heard by the night fighter when the latter was
within 3 km of its target. Within eight weeks the first Karuso
equipment was ready and a total of 100 were built. With the
cessation of the bombing of England in about May 1941, the
majority arrived too late and Karuso was only used once in a
limited number of aircraft in a bombing operation when, P/W
believed, Plymouth was the target.
20. When in 1943 trouble with British night fighters was again
being experienced in the Mediterranean, the Karuso sets were
sent down to that theatre. There, however, the range of
British A.I. was found to be about 4 km. instead of 2 km., so
that the power output of Karuso had to be boosted to give it a
range of 5 km.
21. The method employed was barrage jamming using two bands
(100 - 110 mc/s and 110 - 120 mc/s) with mechanical condensertuned
sweep through the band. There was not room for two
transmitters in one aircraft so only half the band could be
covered in any one German bomber. Karuso III, a later
improvement, was to be capable of being tuned through 100 -
150 mc/s band but so far as is known, it was not put into use.
22. Subsequent tests of Karuso indicated that it had
insufficient range, and by December 1944 the Starnberg, which
was developed in 1940 by D.V.L. as a jammer against radar, had
also been tried out but was likewise considered inefficient. A
new set named Nervtöter was under development but never came
into operational use.
23. It was decided that the jamming of R/T would be of value
against air activity when the invasion took place and prior to
D-Day some 50 or 60 modified Karl II jammers had been formed
into a Stördorf (= jamming village) and assembled at a site on
the Channel coast near Dieppe. With this assembly of jammers,
all possible frequencies in the 100 - 150 mc/s R/T band could
be covered.
24. A few days before the invasion the site was carpet bombed
by the Americans and although the jammers had been somewhat
dispersed, 90 of them had their aerials damaged or were put
out of action. There was some delay in bringing up reserve
motorised units and the invasion took place before they
reached the Channel coast. As a result, no countermeasures
against fighter R/T took place during the invasion.
25. In November 1944 a limited amount of jamming of fighter
R/T in the 70 - 100 mc/s band was carried out on the western
front by motorised units and from a few fixed sites. These
countermeasures were on a restricted scale, owing to lack of
apparatus, but it was hoped to interfere with Allied ground
control of fighters and fighter R/T.

AIR-TO-AIR R/T.
26. During defensive operations over the Reich against Allied
aircraft, countermeasures were very rarely used owing to the
insistence of the "Y"-service on the value of D/F’ing
transmissions, particularly as the German early warning radar
was heavily jammed. Early in 1945, however, it was planned to
create four jamming villages (Stördorf) each with ten Karl
transmitters in order to jam R/T during raids over German
territory. The use of airborne jammers to carry out the same
task had been considered but it was felt that airborne jamming
was less rational than jamming from ground stations because
the frequencies had to be constantly monitored.
27. By the end of the war a new jamming transmitter called the
Feuerland had been developed by Blaupunkt. This allowed noise
modulation to be used in addition to the more generally used
Reichspost modulation. A few sets were sent up to the Holstein
area just before the capitulation, but it was believed that
they had never been used in operations.
28. The standard type of modulation which had been developed
by Reichspost consisted of a number of "Kipp" frequencies -
sharp triangular pulses produced by blocking oscillators -
superimposed on the carrier wave. Tests of its effectiveness
at audio frequencies were carried out early in the war and a
statistical analysis of them seemed to show that it was the
most effective modulation against R/T.

RUSSIAN R/T
29. The airborne FuGe.10 was being developed for use as a
jamming transmitter against the 3 - 6 mc/s band R/T used by
the Russian Air Force. This apparatus never came into
operational use.

R.C.M. AGAINST METRIC RADAR
EARLY WARNING RADAR
30. It was in August or September 1940 during the Battle of
Britain that the first German countermeasures were directed
against British ground radar. The site at Mont Couple behind
Calais was used at first, but was gradually extended to a
chain of ground jammers along the whole Channel coast, and
ultimately there were sufficient to have every identified
British ground radar station covered by at least one suitable
jammer.
31. In 1940 the stations jammed were those in the 20 - 30 mc/s
and 50 – 90 mc/s bands. Both ground stations and airborne
apparatus carried in Ju.52's were used. By 1941 a chain of
Karl jammers which also covered the 200 mc/s band had been set
up along the whole coast.
32. During the initial period, various efforts were made to
spoof our early warning radar. The first of these was the
brain-child of Dr. SCHOLZ and was tried out in 1940.
33. Pulses radiated by one of our C.H. stations were picked up
on the ground and re-transmitted on a different frequency to
an aircraft flying some way behind the Channel coast. The
aircraft re-transmitted the original radar pulse on the C.H.
frequency, but a slightly different phasing, so that a phoney
blip located over the Channel was received. Owing to the ease
with which this phoney blip could be D/F'd and the spoof
immediately revealed by a second station, this method was soon
discarded.
34. About the beginning of 1941 a special experimental
equipment called the Garmisch Partenkirchen, which produced no
less than five different phasings and five phony blips, was
tried out. For the same reason this was not much used in
practice.

How the "S & G" Got Through.
35. The first big operation on which the jamming chain against
British radar ground stations was used was on the occasion of
the passage through the Channel of the Scharnhorst and
Gneisenau in February 1942. A few days prior to the operation
Dr. SCHOLZ was specially brought from Berlin to supervise it.
36. The radar cover of our C.H. and C.H.L. had been carefully
plotted and it was ascertained that the ships would come
within its range as they passed off Fecamp, where they were
due at 10 a.m. At that hour every available jammer was
switched on. The fact that the ships passed through unscathed
was, in P/W's opinion, the best proof of the effectiveness of
the German countermeasures. P/W was not aware that we had
either decimetre or centimetre radar in operation at this
time.

Siege of Malta.
37. In July 1942 P/W was sent to Sicily to take charge of an
intensive jamming programme which he suspected was to be the
precursor of the invasion of Malta, although he was never told
so officially. The first four Karl jammers on 193 mc/s were
brought into service in the neighbourhood of Noto en 3rd July
1942 and the number was later increased to eight, to cover
both A.I. and ground stations. They were beamed on to the
sites at Malta. These transmitters were half kilowatt, C.W.
amplitude-modulated at 100 c.p.s. using an unsmoothed HT
supply, plus a modulation of 150 - 200 kc/s. The reason for
the amplitude modulation being unsmoothed was that there was a
shortage of high-voltage smoothing condensers.
38. After a time it was observed that we had adopted frequency
changes. The German jammers were however, controlled by
monitoring receivers on sites so arranged that the jamming
signals and the original radar signals could be seen side by
side on a C.R. tube; this enabled the frequency change to be
followed within a few seconds. A great aid to them in
following and preparing for these changes was that new
frequencies were invariably tried out during the day from
Malta and the monitoring service could warn the jamming
operators of frequencies likely to be employed.
39. It was noticed that signals on the 50 - 80 mc/s frequency
were switched on during a raid and it was suspected that they
were due to the height-finding equipment of the radar station
controlling our night fighter which seemed to operate in a
similar fashion to the German Würzburg. This opinion was
confirmed when "Y" service heard a ground station say that
they could give the range of the bandits but that height
measurements were not yet available.
40. To jam the "height-finding" frequencies a Ju.52 fitted
with eight jammers covering the 50 - 80 mc/s band was brought
down to Catania. An hour before a raiding force became
airborne this aircraft left Catania to patrol half way between
Sicily and Malta and jam this band.
41. After P/W left, jamming was also carried out on the 42
mc/s band with the same type of Karl ground transmitter as was
used for other frequencies.
Modulation of Jammers.
42. When jamming out ground radar, H.F. modulation was always
preferred to noise modulation since the equipment necessary to
produce a given effect with noise modulation was much more
extensive than for H.F. modulation, and in particular a large
number of high-power valves was needed. The greater efficiency
of noise modulation was not considered sufficient to warrant
the extra power and extra equipment needed. It was also
thought unlikely that H.F. modulation could be filtered out of
the radar receiver without severe deterioration of the
picture.

Düppel (Window).
43. The idea of using window to spoof ground radar had
occurred to the Germans in 1941 and a series of experiments
was carried out in great secrecy over the Baltic in February
1943 (See A.D.I.(K) 334/1945 Part, IV). Very careful
arrangements were made to ensure that the wind was in the
right direction so that the window strips would fall into the
sea and not in Sweden, or even on German occupied territory.
44. The effect of window was observed on all types of German
ground radar deployed along the Baltic coast, and its efficacy
as a countermeasure was realised. The German codename for
Window was "Düppel" - a word with a very similar pronunciation
to the German word "Dipol" (= dipole), indicating the function
of the metal strips.
45. The Signals Staff realised that Düppel was a two edge
weapon and although its development was completed sometime in
1942, and a certain quantity was manufactured, no use was made
of it for fear of Allied retaliation.
46. The whole project was, in fact, kept so secret, that only
a very few high officers and technical experts in the G.A.F.
were aware of the scheme. So closely was the secret of Düppel
guarded that the scientists were not even allowed to carry out
research work to discover what anti-window measures could be
applied to the various types of German radar.
47. Although the Germans were free to employ window as a
countermeasure over this country after its first use by the
R.A.F.in July 1943, it was realised by the Signals Staff that
they had never used it to such good effect as the Allies.
48. The reason was that the small German bomber aircraft like
the Ju.88 could only carry a very limited quantity and
therefore could not produce a real window cloud. They
therefore decided to drop small quantities scattered over a
wide area in the hope of deceiving the night fighters and of
producing the impression that a larger number of aircraft was
engaged on a certain raid as well as in the hope that ground
controllers might vector night fighters on to a window cloud
instead of on to an aircraft.

Final Policy against Early Warning Radar.
49. The general policy followed by the G.A.F. at the end of
the war with regard to the countermeasures against early
warning metric radar appear to be summarised in a document
dated December 1944, which states that the use of ground
jammers against all ground radar is, in principle,
particularly desirable during German bomber raids on enemy
territory, but that there is no advantage in using airborne
jammers because the frequency of the ground radar has to be
constantly monitored and followed.
50. This principle was not strictly adhered to because an
airborne jammer for the 170 - 220 mc/s band named Kettenhund
was used to a small extent in raids on the South-West of
England in May 1944 (sec A.D.I.(K) 321/1944) but it was not
considered to be very effective.
51. Some attempt was being made to develop a noise-modulated
airborne transmitter named Wolke but it was never used
operationally.

METRIC A.S.V.
52. The first attempts to jam A.S.V. were made in the Channel
in the summer of 1942. During the preparations for the
proposed invasion of Malta it was found that reception of
British A.S.V. transmissions was obtained at extraordinary
ranges in the Mediterranean area. This was ascribed largely to
the fact that the receivers were placed as high as possible -
in some cases 3,000 foot above sea level - and attempts were
made to jam A.S.V. by using Karl transmitters placed near them
on high points of the coast of Sicily, Greece and Crete.
53. At about this time a Sonderkommando KOCH was formed and
based at Athens-Kalamaki. Its duties were to monitor and jam
A.S.V. and it was thought they used the Kobold airborne
transmitter with a frequency range of 160 - 200 mc/s. It had
the disadvantage that it could only be built into large
aircraft and some doubts arose as to whether it was very
effective.
54. Up to the of the war, the Bari ground jammers continued to
be employed against A.S.V., particularly along the length of
the Adriatic and along the Norwegian coast at points where
German coastal convoys obtained no cover from islands lying
off the coast.
55. In mid-1943 U-boats leaving Brest were suffering a serious
increase in losses owing, it was thought, to the use of our
A.S.V. a Sonderkommando Rastädter was formed with a few He.111
and Ju.88 aircraft for the purpose of listening to British
A.S.V. on metric and centimetric wavelengths and determining
what type of radar was being used with such effect (see
A.D.I.(K) 38/1944). These aircraft carried, amongst other
receivers, both Naxos and Korfu. The net conclusion reached as
a result of these investigations was that Coastal Command was
using a centimetric frequency (presumably H2S) for which the
Germans had no jamming transmitter.
56. The Allied attacks on U-boats took place so far from the
coast that ground jamming of A.S.V. on metric wavelength was
impossible and too many aircraft were needed to carry out
efficient airborne jamming. It was feared, too, that if
airborne jamming were carried cut, it would only attract
A.S.V.-equipped aircraft or surface vessels to the vicinity,
and be a proof that U-boats were about.
57. Warning receivers were therefore installed in U-boats. The
first of these - Metox - was used against metric A.S.V. It
suffered from the disadvantage that its local oscillator
radiated strongly, and it was suspected that we could home on
to this radiation from 100 km.; the Samos receiver later
replaced Metox. A form of Naxos was introduced to provide
warning against 9 cm. A.S.V. and was used up to the end of the
war.

METRIC A.I.
58. The weak link in the British night fighter organisation
was, as already mentioned, considered to be the R/T
communication; the airborne jamming of British A.I. itself by
German bombers or special R.C.M. aircraft was not considered a
practical measure because it was believed that British night
fighters would be able to home on to the jamming aircraft and
severe losses were therefore to be expected.
59. No intentional jamming of Mark IV A.I. was ever carried
out from the air or from the ground, although it was
considered possible that Karl jammers against G.C.I. and
harmonics of the Heinrich transmitter against Gee, and
possibly of all transmitters jamming Oboe and C.H., may have
had some effect.
60. In this connection P/W stated that it was extremely
convenient for the Germans that we had so many equipment
working on such a restricted frequency band in the 200 mc/s
region. This fact has eased their jamming problem very
considerably.

GEE.
61. The value of Gee system of navigation referred to by the
Germans as Hyperbel, is that it allows an aircraft to navigate
by a radar method without transmitting any signals which could
be used to D/F the raider from the ground. This threat was
realised by the Germans in March 1942 when the existence and
method of operation of the system was first discovered, but
the decision to jam Gee was not taken until August 1942.
62. A jamming transmitter was hurriedly improvised out of the
standard A.S. ground transmitter used for R/T traffic with the
FuGe.16. This was modulated with the standard "Mont Couple"
modulation at 150 - 200 kc/s. Prior to this makeshift coming
into use, a certain Dr. MÖGEL had experimented locally with
jamming transmitters but these only operated for a short time
and no details are known of them.
63. An order for a large number of suitable jamming
transmitters for countering Gee was placed in August 1942 and
the first of these - 1/2kw. Heinrich - went into service in
November 1942. As the Heinrich transmitters became available
in quantity they were deployed all over Germany and by the end
of the war some 270 were in operation against Gee.
64. Estimates of the effectiveness of jamming by the deployed
Heinrich transmitters were obtained by flying captured Gee
equipment and by questioning British P/W. The conclusion
reached was that before the invasion the Gee chains were of no
use further East than 4°.
65. After the invasion the situation changed, and in August
1944 a so-called Stördorf (= jamming village) was set up on
the Feldberg in the Taunus area and controlled and run by the
Reichspost Zentrale. Installation began in August and in
September the first equipment came into use.
66. The Gee countermeasures from the Feldberg site were of a
different type. In addition to a number of normal Heinrich
transmitters, three new types of much greater power were used.
These were Feuerzange, a very powerful pulse transmitter with
a peak power of 1 megawatt, Feuerstein with a peak power of
120 kw. at 5,000 pulses and a smaller transmitter, Feuerhilfe
with a power of 30 kw. which had been improvised by Köthen.
These three powerful transmitters were used to pick up the Gee
transmissions and retransmit them but with a very slightly
different p.r.f. A keying arrangement was incorporated so that
the pulses of the master and slave stations could be imitated.
67. In the immediate neighbourhood of the site it was expected
that the pulse powers used would be so high that the Gee
presentation screen would be completely jammed. At greater
distances aircraft would receive on each frequency used three
or four false pictures broadcast by the Feuerzange and
Feuerstein. As they transmittal their spoof pictures on
p.r.f's which differed only slightly from that used by the
British stations, the effect produced was that the false
pictures wandered very slowly over the true pictures so that
it was difficult for an operator to tell which was the correct
set of blips.
68. At the beginning an insufficient number of sets was
available to carry out this spoofing on all the chains, but by
January 1945 the site was fully equipped. The Germans were
convinced that this system was successful because on 2nd March
1945 at 1230 p.m. a number of fighter bombers paid them a very
unwelcome, visit and completely destroyed the site.
69. Consideration given to the idea of jamming the link
between the Gee ground stations, was never carried out as it
was thought that we would certainly anticipated such measures
by providing a number of reserve links, possibly on centimetre
wavelengths, or oven co-axial cable links.
70. When Gee jamming was first properly undertaken towards the
end of 1942, a large number of monitoring stations placed
about 100 km. apart were erected around the occupied coast
form Brest to Norway. Each site had two Heinrich transmitting
units, one operational and one spare, and monitored all
possible wavelengths. Changes of phase were also reported so
that German aircraft flying with Gee equipment could be
notified by W/T.
71. The whole problem of Gee jamming was considerably
simplified on the few occasions that we made unexpected
frequency changes, because our transmitters lined up on the
new frequency before they were used operationally. Had this
not been done the effectiveness of the German jamming program,
might have been considerably reduced.

LORAN.
72. As has been mentioned in a previous report of this series,
the discovery of Loran came as a great shock to the Germans
because Professor von HANDEL had convinced himself that a
long-range, comparatively long-wave pulse system would be too
inaccurate for employment as a means of navigation. The
Germans' first knowledge of the system was obtained about the
middle of 1944 when maps were captured, and ultimately a
complete apparatus was obtained from an American aircraft.
73. Attempts were made to jam it, and by March 1945, 10 to 20
one kW noise jammers, which jammed the ground wave
satisfactorily within a radius of 50 to 100 km., were in
operation. At this time transmitters to meacon the pulses were
being built and consideration had been given to jamming the
synchronisation of the transmitters from the ground, using a
100 kW. C.W. transmitter which was to be erected as near the
front line as possible in order to be near the ground link.
74. The transmitter was ready and hat been taken to Thüringen
but the disruption of transport and communications prevented
it ever being used operationally.

G.II.
75. The same equipment was used for jamming G.H., known to the
Germans as Diskus, as was used for jamming Gee.
76. A number of jamming villages (Stördörfer) with from two to
eight Heinrich transmitters were deployed throughout Germany.
It was calculated in December 1944 that at 20,000 feet G.H.
could only be received and used up to a line joining Emden and
Kassel and from there swinging South in an arc to Stuttgart,
while at 33,000 feet reception was thought to be possible up
to an arc joining the mouth of the Elbe, Weimar and Augsburg.
77. In addition, it was planned to use the powerful Feuerzange
and Feuerstein transmitters in an attempt to trigger-off the
ground stations from the Feldberg/Taunus Stördorf used to jam
the Gee chains.

OBOE - METRIC WAVELENG.
78. In the autumn of 1942 a new type of radar signal in the
200 mc/s band was picked up by the German monitoring service
at Calais. Statistics were kept and it was observed that these
transmissions occurred mainly at night, and seemed to be
associated with British M.T.B. activity in the Channel.
79. In about June 1943 the same type of radar signals was
heard in Essen during a very heavy bomber raid on Cologne and
Dr. SCHOLZ was able to correlate them with the dropping of
T.I's visually observed. It was realised at once that these
signals were the same as those heard at Calais and an
immediate investigation was carried out. For this purpose a
"noise investigation commission" was formed and a special
experimental Freya with a number of D/F receivers was set up.
The Freya was used to plot the course of the T.I.-carrying
aircraft while the receivers D/F'd and monitored the signals.
80. Some 6 to 8 weeks after the signals had first been
attributed to path-finders, a satisfactory story had been
worked out by the Germans as to how Oboe, called by them
Bumerang, worked. When this had been accomplished, subsequent
Oboe raids were systematically monitored by the normal
monitoring service.
81. At this time (August 1943) plenty of jammers were
available because of the reserve apparatus available for use
against 200 mc/s radar stations on the Channel coast. Ten
sites were chosen to give jamming coverage over the Ruhr and
eight ½ KW MCW Karl jammers employed at each site. The
standard Mont Couple modulation also used against C.H.L.
stations was applied giving 150 mc/s sine wave modulation at
100 c.p.s from an unsmoothed H.T. line.
82. The radio frequency was determined by picking up the
aircraft return signal and tuning the jamming transmitter
until the normal signal failed. Four frequencies in the 200
mc/s band were ultimately detected, but though the ground
station frequencies were found to be steady, those of the
airborne transmitter were not very stable.
83. Aerials recovered from crashes appeared to be mounted
sometimes en the starboard wing and sometimes on the port wing
of the aircraft. This fact, combined with some information
obtained from a British P/W, caused the Germans to believe
that the aerials were directional, and in order to jam more
successfully, all transmitters were moved to the West of the
Ruhr.
84. Jamming was almost entirely confined to the Ruhr area
because this territory was far away, the most important target
within the limited range of Oboe. The Germans were greatly
relieved when Oboe was used against the rocket sites in
Northern France, as the pressure on the industrial Ruhr was
thereby reduced. From about December 1943, intermittent
attempts were made to jam Oboe ground stations from the site
at Mont Couple behind Calais. These were not very successful -
a fact which was attributed to the beam width of British
aerials.
85. In June 1944 a new form of jamming which was known as the
Ballverfahren was suggested. This was essentially meaconing,
using an A.B.G. responding transmitter in the hope of
confusing the aircraft's return signals to the ground station.
It was believed to work well, and P/W quoted as an example a
raid on Nürnberg when aircraft deviated from their course as
soon as the jamming was switched on and returned to their
course when it lifted.
86. An instance of the success of Oboe jamming on the Ball
system was quoted. In June 1944 an oil installation - possibly
Wanne-Eickel - was the target, and all Oboe aircraft were
successfully jammed. The T.I's were dropped late and some 8 km
away from the target. As a result of this the main bomber
force spread out and many aircraft were shot down.
87. Only one metric Oboe receiver fell into German hands and
that was 90% destroyed; although the Germans knew the
principle, therefore, the details of the airborne set were
lacking, and the effectiveness of jamming could only be judged
by the accuracy of bombing.
88. By observing on a Freya the point at which bombs left the
aircraft, the Germans estimated the accuracy of Oboe as 300 x
300 metres for bombing from 9,000 metres, but a further 200
metres of ballistic inaccuracy occurred, giving an effective
error of 500 x 500 metres in the Ruhr area.
89. The success of jamming Oboe was considered to depend
partly on the training of personnel, so it was less effective
on a new target than on an old target which had been jammed
before. It was finally believed that the jamming was 90%
effective.
90. The Germans claim to have been so familiar with Oboe that
they were able to plot aircraft and withhold their jamming
until the aircraft turned onto the bombing run. They were then
able to identify the real target and localise the air-raid
warnings so as to disturb industrial production in the
neighbourhood as little as possible.
91. It is of some interest that on several occasions there was
a consistently good concentration of bombs in an open field
near Leverkusen, which P/W presumed to be due to an error in
computing the exact location of the target.

COUNTERMEASURES AGAINST RADAR.
OBOE - CENTIMETRE WAVELENGTHS.
92. Signals which were recognised as Oboe by the type of
coding were detected on a wavelength of 9 cm on the Channel
coast about the spring of 1944. The normal monitoring service
had previously intercepted unexplained 9 cm. signals in
October 1943 but had not finally connected them with Oboe.
93. When 9 cm. Oboe was recognised, it presented the Germans
with a great problem, as no jamming valves were available for
that frequency and German intelligence had not given any hint
that a centimetre version of Oboe might be produced.
94. By July 1944 a valve called LD.7o (= 7 ohne = without) had
been produced, which was an LD.7 valve without cooling fins. A
transmitter unit called Feuermolch, tuneable from 8.6 - 9.6
cm., pulse modulated and giving 3 kW peak pulse power, was
than built. The whole apparatus, a Feuermolch transmitter
together with a mirror reflector to achieve 200 km. range by
beaming, was called Feuerball or A.B.G. (Anti Bumerang Gerät).
95. Jamming on 9 cm. Oboe was first used in operations in
October 1944 at Weser and Leuna. The Feuerball jammer was used
as a pulse repeater, after the frequency had been established
by interrogating the aircraft. The jammer then set up ringing
between the aircraft and jammer on the Ball system used
against metric Oboe.
96. The latest type of centimetric meacon responder called
Feuerburg had receiver and transmitter aerial mechanically
linked to follow individual aircraft, the jammer aerial system
giving a beam of 13° width. The aircraft was followed by hand
by means of a spinning dipole in a receiving dish.
97. According to Dr. SCHOLZ the wavelength originally used by
British centimetric Oboe was 9.26 cm. Sites were set up with
both 200 mc/s and 9 cm. jammers so that either could be
selected by a change-over switch on the receivers.
98. The jamming of Oboe by spoof massages was never tried
although the meaconing jammers were fitted with a keying
arrangement which would have allowed them to attempt this.
99. Oberleutnant Dr. BÄHRE of Ln. Versuchs Regt. Köthen had
doubts as to the effectiveness of the Ball system and had
proposed building a jammer with a very high p.r.f. to saturate
the aircraft receiver with pulses so that the strength of each
individual pulse re-radiated by the aircraft transmitter would
be greatly reduced and the range of the system would therefore
be considerably decreased. The Roland J transmitter which had
been designed for H2S countermeasures was to be adapted by
Lorenz for this purpose, but the idea was never put into
operation as the end of hostilities occurred shortly after it
was made.
100. An example of the success of jamming centimetric Oboe was
quoted and concerned a series of five raids on Gotha. Three
attacks, each with between three and five aircraft, were
unjammed and all scored hits on the railway station. The
fourth attack was jammed and no hits were scored on the same
target. The fifth attack was again let pass without jamming
and the station was once more successfully hit.
101. A further proof of the efficiency of the Ball system was
that in plotting aircraft a diversion from track could be
induced when the jammer was switched on and the aircraft would
return to track if the jammer were switched off again.
102. On the only occasion on which a 9 cm. Oboe aircraft was
known to have been shot down, it crashed in the Zuider Zee in
shallow water where it could neither be reached from shore nor
by sizable ship, and it was not possible to salvage the
equipment. As a result, the Germans never obtained any Mark II
Oboe equipment and detailed information as to how the system
worked was always lacking. There was no explanation, for
instance, of why certain aircraft transmitted pulses which did
not appear to have normal Oboe coding, although the aircraft
flow at heights and along tracks which obviously identified
them with Oboe procedure.
103. No advance information of the target could be obtained
from these aircraft but this was easily obtained from the W/T
transmissions between ground stations. The W/T channel used
was also monitored in order to see if jamming had been
successful. It was also noticed that some aircraft would not
respond to the interrogator but the reasons for this were not
fully understood. These aircraft seemed to be operating on a
wavelength above 9.6 cm.
104. A new valve to cover the 9.6 - 10.6 cm. band was being
produced by Dr. GROOS. It was a 100-watt Klystron and it was
proposed to jam with its aid as soon as it was finally
produced.
105. Towards the end of the war there was a great increase in
the daylight use of Oboe but P/W did not believe that the
Americans had ever used it. With so many aircraft over Germany
towards the end of the war correlated evidence was not
available.

H2S.
106. Shortly after the discovery of H2S in January 1943 panic
orders were given for the production of a jammer. Later in the
year Roderich, which was manufactured by Siemens and which
used a Magnetron of theoretically 5-watt power, was made
available. The transmitters were unbeamed and the power was so
low that they were useless. By 1944 the use of Roderich had
been discontinued.
107. The difficulties of jamming highly-beamed centimetric
radar were so great that it was decided that all that could be
done was to attempt to defend a few vital targets. The first
target to be chosen was the Leuna works which was considered a
good target.
108. The Reichspost Zentrale was called on for assistance and
Dr. GROOS of that institution successfully developed a
Klystron valve, which was a water cooled 100-watt valve
tuneable by hand from 8.5 - 9.5 cm. This was built into the
jamming transmitter which was known as the Postklystron.
109. In order to concentrate as much of the energy as possible
to the aircraft, horns or paraboloid aerial reflectors were
employed with the transmitters. About eight sites around Leuna
were chosen, bearing in mind that the attacks always seemed to
use a route coming in from the North, presumably because the
best H2S pinpoints lay in this direction.
110. Four Postklystron transmitters were placed on suitable
sites and spaced in frequency across the observed 30 mc/s band
of H2S by putting them about 5 mc/s apart and making use of
the side bands from 2 - 10 mc/s single frequency amplitude
modulation. This barrage was used with low directivity.
111. A second type of jammer employed made use of the Roland
transmitter built by Siemens, which had a 30° beam, but its
development was abandoned about March 1945, as it was not
considered very successful.
112. In yet a third system Postklystrons were used with a
beamed aerial system giving a lobe 6° wide. The transmitter
was coupled mechanically to the D/F, receiving aerial of a
Korfu receiver, its aerial being provided with rotational
eccentric split. The receiving aerial was trained on a single
H2S bomber, which was followed manually.
113. The detection range for setting up was about 300 km. With
the less beamed type, Roland, effective jamming ranges up to
about 30 km had been obtained but with the narrow 6° beaming
the H2S tube was completely obliterated at 40 km if the beam
was focussed on the H2S aircraft.
114. One P/W had flown with H2S equipment installed in German
aircraft in order to carry out experiments in ground
camouflage against H2S with the aid of corner reflectors. The
conclusion was that corner reflectors were ineffective. It had
originally been planned to cover arms of the sea and lakes
with corner reflectors, but in the first place too many were
needed, and in the second place arrangements had to be made
for these to remain fixed in a certain orientation in order to
produce an effect.
115. Another suggestion had been made that metallic powder
could be used to increase the reflectivity of an area. This
was obviously no use as camouflage for a target, which was the
end originally in view. Consideration was given to producing a
dummy target with its aid but it was concluded that the
quantity of powder necessary was so enormous that it was not a
practical proposition.

H2X.
116. The Germans had such leeway to make up with the production
of 3 cm valves that no active countermeasures against H2X had
been put in operation up to the end of the war. Development of
a transmitter called Roland 2 was started in December 1944
with Telefunken Ceramic 3 cm valves believed to be known by
the designation LD.72 and LD.77.
117. The set was to be modulated by 100 kc/s pulses and to
sweep through a small radio frequency band. The power achieved
was 50 watts average. With horn aerials a 20° beam was to be
achieved. The range against an H2X set which had been captured
undamaged at Wiesbaden was 20 km. in the initial experiments.

A.I.
118. Owing to the strong beaming and method of sweep of
centimetre A.I. the G.A.F. was doubtful if any jamming would
be possible. No airborne transmitters against centimetric radar
were developed.

-o-o-o-o-o-o-o-o-o-o

ACKNOWLEDGEMENT.
Acknowledgements are due to the various technical bodies,
both British and American, who collaborated in producing the
technical information contained in this report.
A.D.I.(K) and S.D.Felkin,
U.S. Air Interrogation. Group Captain.
29th August, 1945.

A.B.G. (DALL)
The A.B.G.(Anti Bumerang Gerät) meaconing jammer was first
used in June 1944 and was an idea fathered by P/W. It was a
responder beacon which was employed against Oboe to set up
"ringing" between the aircraft return signal and the A.B.G. so
that the aircraft return to the ground station was confused.
The jamming transmitter had a 20 - 30 kW power in the case of
the model used against 200 mc/s Oboe. In the A.B.G. used
against 9 cm. Oboe (Feuerball) the power was 3 kW.

BRESLAU.
This was the pulse modulated transmitter with a range from
20 - 250 mc/s developed and built in the G.A.F. laboratories
in PARIS. It was believed to have consisted of six or eight
½ kW transmitters. Some 50 sets only were put in hand and
about half of them were completed. It was thought that they
had been used against ground radar stations along the Channel
but with what success it was not known.

FEUERBALL.
This was the name for the A.B.G. centimetric responder used to
jam centimetre Oboe. The jammer was used as a pulse repeater
and set up ringing between the aircraft and the jammer. It
consisted of a transmitter using a klystron valve developed by
the R.P.Z. which covered the frequencies 9.0 - 9.6 cm., backed
by a beaming reflector. The peak power was about 3 kW.

FEUERBURG.
In order that the Feuerball transmitter should be beamed on to
the transmitting aircraft, a beamed receiver was mechanically
linked to the Feuerball set. The receiver was operated so that
the receiving mirror was aligned on the aircraft and the
Feuerball paraboloid mirror followed any changes of elevation
or direction made by the receiving operator. This complete
set-up of beamed Korfu receiver with a Feuerball beamed
transmitter was known as Feuerburg.

FEUERHILFE.
This was a smaller form of Feuerstein improvised by Köthen
with a peak pulse power of 30 kW.

FEUERLAND.
This was a two-stage inductive transmitter (final stage
LS.1000) manufactured by Blaupunkt and served the same purpose
as the Karl II. The first production sets were ready in March
1945 and were believed to have been sent to the Holstein area,
but they were never used operationally.
The frequency of the Feuerland could be adjusted from
30 mc/s to 300 mc/s by means of interchangeable H.F. coils.
Different types of modulation could be introduced according to
whether it was to be used against R/T or radar. Against R/T it
was known to have had the four-tone chime modulation described
under Nervtöter below. It could also be used with noise
modulation with an adjustable bandwidth up to 2 mc/s. The
power output was about 350 - 500 watts.

FEUERMOLCH.
This was the name given to the centimetric transmitting
equipment of the Feuerball.

FEUERSTEIN.
The Feuerstein designed by Telefunken was used for producing
a false picture on Gee sets, the keying of the pulses being
carried out by equipment supplied by Telefunken and Siemens. A
number of these sets were installed on the Feldberg. It was a
high-power pulse transmitter at frequency range of either 20 -
52 mc/s (known as the Feuerstein 1) or 48 - 90 mc/s (known as
the Feuerstein la). At a p.r.f. of 5,000 cycles it had a peak
power of 120 kW.

FEUERZANGE.
This was the highest-powered pulse transmitter possessed by
the Germans and was used in 1945 on the Feldberg to provide
spoof Gee transmissions. The transmitter, developed by Dr.
FREUDENHAMMER and built by Siemens, was water-cooled and could
be modulated in exactly the same way as Feuerstein. The
frequency range of the transmitter was 20 - 87.5 mc/s and at a
p.r.f. of 5,000 cycles a power of 1 megawatt was claimed. It
was considered a very effective set but only came into
operation towards the end of 1944.

GARMISCH PARTENKIRCHEN.
Garmisch Partenkirchen was believed to be an improvised
airborne apparatus, probably manufactured by Neufeld and
Kuhnke of Kiel. It was used to a very limited extent in 1941.
It consisted of a receiver which picked up a ground radar
transmission and re-transmitted on the same wavelength but
returned no less than five different pulses with slightly
different phases with the object of creating false echoes. As
these false echoes could be immediately identified if a second
ground radar D/F’d the jamming aircraft, the idea was carried
no further.

GEWITTERZIEGE.
An experimental spark, ground jamming transmitter for
employment against flight radar and using a 1/2 wavelength
dipole aerial in front of a reflector, was given the code name
Gewitterziege. The band width was very large but it was
claimed that it was an effective jammer at close range.

HEINRICH.
This transmitter was developed by the Reichspost Zentrale in
1942 with the specific intention of providing the G.A.F. with
a jammer against the Gee navigation system. A large number of
these sets was built and deployed all over Germany to jam Gee.
A set of the same type, from which Heinrich had been
developed, was used in Sicily in July 1942 for jamming the
radar stations in the 50 - 80 mc/s band in Malta.
In its ultimate form, Heinrich II, the transmitter had a
power of 500 watts and covered the band from 20 - 90 mc/s in
four separate sections. For this output it used four LS.180
valves arranged in parallel push-pull.
It was 100% modulated by 150 kc/s sine wave with the
addition of 100 cycle ripple obtained from an unsmoothed H.T.
power supply. The set needed only two controls, one for the
main tuning and one for the aerial coupling.
The aerial consisted of a wide band dipole of squirrel cage
circular section, with normal tapping at the feeding point.
This one aerial was used in the entire frequency band from 20
– 90 mc/s. It was stated to have a standing wave ratio of 20%
in voltage.

KARL I.
This was the standard jamming transmitter for use against
British radar and was designed to cover the frequencies 90 -
250 mc/s in two bands. Development work on it was started at
the end of 1940. The transmitter employed four LS.180 valves
and had a power output of between 300 and 500 Watts. It was
modulated by the standard Mont Couple 150 kc modulation on
which a 100-cycle tone coming from an unsmoothed 50-cyle
source of supply was imposed. The type of modulation employed
could not be changed in the field.

KARL II.
This was on improvement of Karl I with few changes in the
electrical specifications but it was really composed of two
more powerful Karl I units with a common feed. It was also
modified so that any desired standard type of modulation could
be substituted at the site where it was employed, thus
obviating the necessity for returning the transmitter to the
factory, as was the case with Karl I.
The Karl II employed an LS.1500 valve with an output of
2 kW, and besides being used against ground radar, it had been
modified for use against R/T with the Post type of modulation.
It was not known what degree of success had been achieved with
this set.

KARUSO.
The original Karuso I was improvised by the R.P.Z. with the
specific object of providing aircraft with an airborne
transmitter to jam the R/T link between the British ground
control stations and British night fighters. It was origina11y
intended to sweep through the whole 100 - 120 mc/s band. 0wing
to the relatively large frequency sweep, however, jamming was
not vary effective, so it was manufactured in two forms, to
sweep from 100 - 110 or from 110 - 120 mc/s.
It had ultimately an effective range of about 5 km. and a
power of about 30 Watts. Altogether, only 100 sets were
manufactured.
The designation Karuso II was given to a development which
never got farther than the laboratory stage, but Karuso III
was produced and covered the 100 - 150 mc band. The width of
the jamming band was only 3 mc/s and the frequencies used was
set up on the ground according to intelligence information
given by the German "Y"-service. It was not known whether this
set was used operationally.

KETTENHUND.
Kettenhund was a 30 watt air-born jammer developed in 1943
by a certain KETTEL of Telefunken covering the 170 - 200 mc
band. It was used against British ground radar stations in
raids over South-West England in 1944. Tests with the set led
the Germans to the conclusion that it was not very effective.
Modulation employed was a triangular wave with a frequency of
several hundred kc/s.

KLYSTR0N.
This was the name commonly applied to a centimetre jamming
transmitter witch was also referred to as the "Postklystron".
It acquired this name because it made use of a centimetre
klystron valve developed by Dr. GROOS of the Reichspost. A
power of 100 watts was claimed for it. It was a CW jammer
which could be tuned by hand between 8.5 cm. and 9.5 cm. It
was fitted with a horn aerial to be aligned on the approaching
H2S force. It was claimed that at a range of about 40 km. the
H2S tube was completely obliterated when the Postklystron was
focussed on an individual aircraft. This set came into
operation about March 1945.

KOBOLD.
The Kobold was an airborne set designed by the Post
specifically to jam A.S.V. and was originally used in the
Mediterranean in conjunction with a Karl transmitter working
from the ground. It was, in effect, half a Karl transmitter
and used two LS.180 valves. A modulation of about 400 cycles
originating from the aircraft transformer was superimposed on
it. It had the handicap that it could only be built into very
large aircraft.

NERVTÖTER.
Nervtöter I was designed as an airborne transmitter to jam
Allied R/T but considerable difficulties were encountered in
tuning it in the air to the frequency observed and it was
never used in operations.
As a result of the criticism made by T.L.R., the Nervtöter
II, which was also believed to be known as FuGe. 40, was to be
developed. This set employed an LS.50 valve in the final stage
and the frequency of the R/T was to appear as a blip along is
time base on a cathode ray tube, while the frequency, to which
the transmitting jammer was adjusted, appeared on a similar
blip on a second time base on the tube. By setting these two
opposite each other the operator could easily see that he was
jamming the required frequency.
A so-called chime modulation of four changing tones was
used. The power output was 25-30 watts and the frequencies
ranged from 90-160 mc/s. Wide band aerials were to be used.
This set had not got beyond the experimental stage by the end
of the war.

OLGA.
Olga was a self-excited, grid-keyed, one valve transmitter
(LS.180) developed by the Navy and had a frequency range of
150 - 200 mc/s and an output of about 300 watts. It was
believed that a p.r.f. of 500, 700 or 900 cycles was used.
This jammer was an early type used against British coastal
watch radar without much success.

RODERICH.
This was the name applied to the first set developed by
Siemens for jamming H2S when panic counter-measures were
called for early in 1943. It used a magnetron valve with a
maximum power output of 5 watts and was virtually of no use
whatsoever. It took some months to develop; in the meantime,
German knowledge of how to Jam H2S had increased to such an
extent that it was never used.

ROLAND.
The Roland jammer was developed for use against H2S by Dr.
WEHRMANN of Siemens and was said to employ a triode
transmitter valve designated L.D.72 or possibly L.D.75. The
wavelength was 8.5 - 9.5 cm. and with the aid of a horn aerial
it produced a 30° beamed transmission, modulated, it was
believed, by 100 kc sine wave and pulses of an unknown p.r.f.
It had less than 50 watts average power. The range at which
obliteration of the H2S tube was claimed, was about 30 km.
The Roland II was the name applied to an attempt to produce
a similar set on 3 cm using, it was thought, a LD.77 triode
valve and a horn aerial a 20° beam. It is doubtful if it was
used operationally as the valves had a very short life.

STARNBERG.
This was believed to be the precursor of Kettenhund and was
designed by D.V.L. Adlershof in about 1940 but never used. In
a document there is an indication that attempts were later
made to use it as an R/T airborne jammer; A.D.I.(K) 231/1944
also gives an account of preparations to use the Starnberg
operationally.

WOLKE
Wolke was believed to be the code name applied to the first
German attempt to imitate a noise jammer like that used by the
Allies. It was believed to use two L.D.5 valves in the final
stage and to have a carrier frequency of 90 mc/s. The average
power output was 15 - 20 watts, the width of the noise band
being about 2 mc/s.
As a result of the examination of Wolke the conclusion was
reached that noise modulation required too many valves and too
much power and that with the some number of valves a better
effect could be obtained with other types of modulation. The
set was therefore used for training night fighter crews to see
through electronic jamming of SN.2."