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 Germany and Great Britain.

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 Europe at that time. But, on looking at this receiver more closely, it was found to be more sensitive than any receiver used just for blind landing. This was the receiver for Knickebein and gave us the final clue to the frequency that the beam operated on. Within days of this discovery another prisoner of war talked about Knickebein and said it was indeed a bomb dropping radio aid and, more important still, that it involved an intersecting radio beam.

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 Derby. This now all tied up with reports from Germany which stated that if they could destroy the Air Force and its supporting Aero industry they would be nearer to finishing off our defence system, and Goering had stated that these targets were to be immediate priorities.

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 Calais, one 5Km and one 50Km from target). Two more beams were transmitted from Calais – the. Navigator now had an early warning of approach plus a 5Km. warning, after this second warning a mechanical clock was started and run up to near target -. then reversed and run down, if correct information had been fed in, i.e. Flight speed etc., the clock would run down to that point where release should be given  – and accounted for the Exponential fall and time to hit target.

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 Coventry was some 300 metres from original estimates.

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 Rhur Valley (Horne of German Heavy Industries)

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 Florennes in Belgium, where the underground resistance network had been informed. They were cubic to give us accurate positions of all markers dropped, even measured in paces from our aiming point.  We now knew we could pinpoint n target from 32,000feet at high speed without using any other Navigational Aid except the control from the two stations in U.K.

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 Rhur Valley were duly marked.

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;-


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.


1. Aircraft transmitters were triggered from ground stations and this was used for all measurements. Accuracy on the fly path 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.

g4cit g4cit2






































Guy V. Eves. G4CIT – December 1978 and June 1979.

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