KNICKEBEIN AND GRUPPE 100 - v - OBOE AND 105/109
What was
Knickebein, how it was discovered, and how it was countered, makes an
interesting story that could almost be described as a thriller. Our own Radio
Navigational System called Oboe, which had many similar features to the
Knickebein system, could be described as the Tit for Tat - a scientific v Radio Battle which
was waged throughout the length of the war from 1939 -1945 between the radio
brains of
Our story begins
in early 1940 when a recorded conversation between two prisoners of war
mentioned an apparatus called “X
apparatus” ( X GERAT) and it was obvious from what was being said that it had
something to do with a Radio Receiver in a bomber and also something to do with
radio pulses.
In March, 1940
a Heinkel 3 from GRUPPE 100 was shot
down and amongst the bits and, pieces salvaged was a small piece of paper
mentioning navigational aids, at the end of the list of aids was the reference
to Knickebein on bearing 315 deg.
The next
reference to this word was from an intercepted Radio signal which gave information
about Knickebein Kleve (Kleve being the town where Anne of Cloves came from), and it looked as though there was a beam
station set up at Kleves, which was the nearest point on German soil to
England, beamed on the U.K.. at 315 deg.
The next step was
the examination of the radio gear on any other Heinkels from GRUPPE 100 shot
down, to see if there was any equipment which would be suitable for the reception
of this beam. The only equipment with anything like it was the blind landing
gear which was used for the Lorenz system, which was standard in
These
investigations were carried out by Flt. Lt. Scott - Fernie, who was an
enthusiastic Radio Amateur and had not long joined the RAF Signals Intelligence
Service.
Just to digress,
for a moment, it should be stated here that the Amateur Radio Community in
Britain were to prove an invaluable reserve to supply staff to the Signals
Intelligence Service and the increasing number of Radar stations.- which of
course in those days were called Radio Location Units and that name was kept
very secret at the time,
Knowing that the
Lorenz receiver in the Heinkel was hotted up and knowing the frequency, the
next step was to find the bean itself - by putting a search aircraft up to
detect the dots and dashes which were the Lorenz signal - and of course there
had to be two beams for the X apparatus one the dot dash bean lying straight
from Kleve on 315 deg. and the other to intersect it over what could presumably
to a target. Fortunately for us this particular beam was found by Flt. Lt.
Bufton and Cpl. Mackie on the night of 21st/22nd June 1940 - flying all night they found a beam
approx. 400 yards wide passing through a point one mile south of Spalding in
Lincolnshire, having dots on the south side and dashes on the north, the
carrier frequency being 31.5 Mhz and modulated by 1150 Hz, with similar
characteristics to the Lorenz system. They also discovered a second bean, but
with dots to the north and dashes to the south and synchronized to the Kieve beam.
This second bean passed through a point near Beeston, Notts.
Those two beams
would converge over the Rolls Royce Aero Engine works in
The interesting
outcome of all these discoveries was that it showed that the Germans had a
technique of Navigational Aids that was generally thought to be impossible and
that now they could place an aircraft within 400 yards accuracy of their target
in this country. It meant that they must have a very precise RDF system, and it
looked as though they were working along similar lines for their bombing as our
CHL system for detection. Their beam aerials by now had been photographed and
they closely resembled the CHL rotary beamed arrays we were using for normal
detection of low flying aircraft.
Alter finding the
‘K’ beams in June, 1940 a special RAF unit was set up - No.80 Wing - to handle counter measures, the
design and development of these measures was in the hands of The (Telecommunications
Research Establishment).
In order to
quickly do something; about the ‘K’ beams, simple Diathermy transmitters were
used from hospitals and placed along the paths of beams - these transmitters
emitted lots of “white noise “on the K Frequencies - but soon a more powerful
equipment code named ‘Aspirin’ (to counter “headache’1 code name for the beam)
was developed which transmitted a Dash similar to the dash in the beam. The Pilot
would hoar this dash even when he was equal signal area and consequently, think
he was too far in Dash Zone and shift over to make the dots as strong as the
increased dashes, this so confused the Pilots that they thought we were bending
their beans and so the legend of Beam Banding vas started.
Before closing
the Knickebein story it is interesting to note that the Germans greatly refined
the system (on previous map draw two more beams from
The potential
accuracy was so great that in calculating the distance to target the Earth’s
Curvature had to be taken into account - which in the case of
A final
interesting point - Gruppe 100 were now dropping flares and Incendiaries as
markers rather than bombs - it looked as though they were now purely marking
for a following force.
Our directional
measurement for the CHL detection of low flying aircraft were not very good - but our
ranging from Station to aircraft was extremely accurate.
The new basic
idea was to fly an aircraft at constant range from Station ‘A’ and then Station
‘B’ would accurately pin point the position along that arc. A transmitter in
the aircraft would pick up the pulses from Stations ‘A’ and ‘B’ and retransmit
them back, this would greatly increase the effective range from the ground
stations as we were not know relying on the “Echo” for return.
The development
of this is idea was placed iii the hands of Dr. F.G. Jones and Mr. A.H. Peeves
of TRE
The system was
started using old CML frequencies, i.e. 200— 250 Mcs, and Station ‘A’s function
was to fly the aircraft at a constant range the arc of which passed over target
- if the aircraft drifted in towards ‘A’ he (the Pilot) was given dots - and if distance increased beyond the arc -
dashes. .Equal signal meant flying accurately along the arc and this “Flight
Path” could be monitored and controlled to a 50 yard bandwidth by Station ‘A’.
Station ‘B’
situated some 100 miles from ‘A’ would dissect that imaginary arc at regular
intervals and being connected to the Navigator could control his run up to
target and advise exact release point.
These ground
stations were operating in an unharassed situation whereas the Knickebein
system had the pilot and Navigator making all decisions re position and release
while facing flak and Fighter problems.
The Oboe Pilot and
Navigator being ground controlled, if the releasing Station ‘B’ did not think
the Pilot was flying accurately in Equisignal - release was not given – consequently the
system built up a reputation for high accuracy.
In order to
ensure the safety and maintain the secrecy of this venture very fast aircraft were
required capable of carrying the Radio gear and marker bombs. The Mosquito was
chosen and two squadrons co-opted (105 and 109). Weather did not new play an
important part due to the Radio Accuracy - in fact 10/10 cloud over target
meant less likely hood of being interrupted by Night Fighters - Flare markers
could he dropped to hang in sky above cloud.
Our main targets
which now came within the range of our ground stations were situated in the
In December, 1942
the calibration of this system was checked by sending a. small force of Mosquitoes
on a marking run on the town of
Krupps, Essen - These
works had been the Target for tonight on many previous occasions, but without
much success, always having to rely on “Bombers Moon” conditions, but in April,
1943 a major effort was made using the Oboe system and 105/139 squadrons.
Station ‘A “
situated on the coast north of Cramer, controlled the Pilot in his Flypath arc
over target, sand Station ‘B’ operating on similar RF frequency but lower PRF
(Pulse Recurrent Frequency) situated south of Dover, cut this imaginary arc at
regular intervals A.B.C.D. up to target such that the Navigator had a precise
position on his approach.
In ground station
‘B’ small mechanically operated computer (counting 20 I.P.S.) was set up giving
a run up time towards target, to a point where it was switched to run down, from the rundown time was deducted the TRF or
Time of Bomb Pall, this calculation was based on; -
Flight - speed - Wind Velocity - Ballistics of Missile, when the
computer reached this point it signaled the Navigator to Release. The flare
markers were dropped in a box formation, such that the heavy force following
(some 600 aircraft) dropped their loads into this area. The results of this
operation exceeded all expectations - Krupps was put out of action, and
following on this the other industries along the
It took nearly 12
mouths before the German Radio Intelligence started to jam the 200 Mcs Oboe Stations,
but even then we were able to work through their jamming by erecting an aerial
beamed on his station in Calais, picking up the maximum signal - controlling
the amplitude - and feeding into our own system in antiphase, within six months
of this jamming however, Randle and Boot of Magnetron fame had presented us with
the first tuneable magnetron - vie were in the 10 cms band and completely
undisturbed until end of hostilities.
The accuracy of
the Oboe system was now acknowledged, and prior to ‘D’ Day was used extensively
to neutralise German heavy defences along the French coastline and destroy all
major rail junctions inland. After the ‘D’ day landing-s this system was
further extended, by equipping Mobile Stations ‘A’ and ‘B’ which were set up in
selected sites in France, Belgium and Germany, to give close support bombing to
our advancing armour, on one of these moves we occupied a German Radar Site
(Florstmar) complete with equipment - not very well destroyed.
A brief summary
of the two systems;-
Knickebein 1. Relied on 4 beams for accuracy (Approx. 400 yards)
but could now be jammed.
2. Air crew had
to make decisions re their final position for release under harassed
conditions.
Oboe. 1.
Aircraft transmitters were triggered from ground stations and this was used for
all measurements. Accuracy on the flypath approximately 50 yards. Some jamming
but this was countered.
2. Air crew had only one responsibility to keep aircraft in Equisignal
and, listen for release - all control came from Ground Stations.
Guy V. Eves. G4CIT. December 1978 and June 1979