Oboe ‘Blind Bombing’ System
Group Captain Keith James ‘Slim’ Somerville joined the Wireless Development Unit (later 109-Squadron) at Boscombe Down. Intelligence & Scientific Officers had identified a Radio Beam from a Transmitter near Cherbourg which was used by the Luftwaffe to guide their Bombers to Targets in England. Somerville and his colleagues had to gather Intelligence about the Beam before mounting a Series of Operations to Fly down it and Bomb the Source. These Missions provided valuable information for the Scientists at the Telecommunications Research Establishment (TRE), who then used the information to Develop a similar Bombing Aid. This early work by TRE and the Aircrew at Boscombe Down led to the Development over the next 2-yrs of the highly accurate blind-bombing aid Oboe, so-called because the Radio Tone heard by the Aircrew was similar to the Double Reed Note of the Oboe Woodwind Instrument. The System was Based on the Transmission of a Radio Beam from Ground Emitters located on the East Coast and Aimed at the Target. Specially Equipped Mosquitoes Flew along the Beam to the Target before dropping Markers & Flares for the Main Bomber Force. Flying a Mosquito, Somerville and his Navigator took part in the 1st Oboe Raid on 20th December 1942. The attack achieved modest success but the experience was gained & Refinements to the System were Incorporated. On 5th March 1943, he Piloted one of the 5-Mosquitoes to mark perfectly the Krupps Factory at Essen, when some of the Markers were Judged to have fallen as Close as 75-yds. In the words of Air Marshal “Bomber” Harris: “This was the precise moment when Bomber Command’s Main Offensive began; the moment of the 1st Major Attack on an Objective in Germany by means of Oboe.” After 2-yrs with Squadron-109, Somerville was Awarded the AFC for his Pioneering Work in Blind Target Marking and Posted to the Pathfinder Force Headquarters. In October 1944 Somerville returned to Operational Status as Squadron Leader of 105-Squadron the 2nd Oboe Equipped Mosquito Squadron. In March 1945 he was Promoted to Group Captain having Flown 117-Operational Flights over Enemy Territory. In April 1945 the Mosquitos of 105-Squadron used their Oboe equipment to pinpoint precise Locations in Western Holland to allow the Main Bomber Force to drop food supplies to the starving Dutch People – Operation Manna.
Telecommunications Research Establishment TRE: 1936 The Team of Research Staff Developing the Chain Home Radar System were transferred from the National Physical Laboratory to the Air Ministry, initially at Bawdsey Research Station (BRS) in Suffolk. Having created the Team, Robert Watson Watt was the 1st Superintendent of the Bawdsey Research Station. In 1938 Watson Watt was appointed Director of Communications Development in May; Albert Percival Rowe succeeded him as Superintendent of BRS. Rowe was to remain Superintendent throughout the rest of the War. In 1939 To protect the work in the event of War, it was decided to move the team to Dundee; the organisation was renamed the Air Ministry Research Establishment. East Scotland was not free from hostile Aircraft, which interfered with the Research at the nearby Chain Home Station. In 1940 The unit was moved again, to Worth Matravers, near Swanage, and put under the Ministry of Aircraft Production. In November 1940 it was renamed Telecommunications Research Establishment (TRE). In 1940 Following the development of the 1st working Magnetron by Boot & Randall at Birmingham University, Radio-location became possible using 10cm wavelength Radio waves, which revolutionised Radio-location. By July the 1st 10cm RDF echoes had been received from an Aircraft. In October the 1st Airborne Interception Night Fighter Operation was conducted under ground-controlled interception. In 1942 TRE developed the Gee Aircraft Navigation system which was 1st used Operationally by Bomber Command in March. In 1942 TRE developed Oboe, a precision ground‐controlled Blind Bombing System, which had its 1st Operational use in December. In 1942 following the successful British Raid on the German Radar Station at Bruneval, it was felt prudent to move TRE from its Coastal position so it was moved Malvern in May; the new Site had space to accommodate the 1000s of workers. In 1943 TRE developed H2S, an Airborne Radar Navigation & Bombing aid and the 1st ground mapping Radar, which was 1st used in Operations in January 1943. In 1943 TRE developed centimetric anti-Submarine Radar which was 1st use by Coastal Command in March. Post-WWII: TRE was renamed the Radar Research Establishment, later Royal Signals & Radar Establishment (RSRE) and finally became part of Defence Evaluation Research Agency (DERA)
Some Lancasters were Equipped with Oboe Equipment. The Technique of Flying with the Target-marking Aid, with Dots or Dashes heard in the Pilot’s Earphones, indicating which side of the Beam he was Flying, required Special Training if the Pilot was to Fly with sufficient Accuracy when the Dots & Dashes merged to a steady Note, indicating that the Aircraft was heading directly for the Target. Although on a “Rest” Tour, Somerville Flew a number of these Missions and he was the Pilot of the 1st Oboe-equipped Lancaster Operation on 11th July 1944 when he led a Formation of the Heavy Bombers to Attack the Flying Bomb Site at Gapennes. Somerville recalled that Beam Flying “needed great Concentration to Monitor the Aircraft Instruments and the sound of the Dots & Dashes, waiting for them to Merge. Once they did, it was vital to Hold the required Heading, Speed & Height while the Navigator listened for the Radio Signal which determined the moment to release the Markers or the Bombs.” This demanding Effort often had to be conducted under Enemy Fire when the Aircraft had to be held Steady. Four days before this 1st Lancaster Operation, an Oboe-equipped Mosquito had Crashed in an area of Fierce Fighting near Caen. The Top-secret Equipment was Salvaged and Somerville Flew over in a Mosquito to bring it back to England before it could fall into Enemy hands.
Oboe was a British Aerial Blind Bombing Targeting System in WW2, based on Radio Transponder Technology. Using Triangulation to determine relative Location, the System consisted of a Pair of Radio Transmitters on the Ground, which sent Signals which were received & retransmitted by a Transponder in the Aircraft (typically a De Havilland Mosquito or Avro Lancaster). By comparing the Time each Signal took to reach the Aircraft, its Location could be Calculated to a fair Degree. In this way, an Aircraft could be Directed Blindly over a Specific Target, all of which were pre-calculated and kept on File. Prior to a Mission, a Circle was drawn around the Primary Oboe Transmitter so that it passed over the Selected Target, with the Primary Transmitter in the exact Centre, and the Radius of the Circle noted. The Transponder Equipped Bomber (or Bombers, 1 at a time) would then attempt to Fly along the Circumference of this Circle towards the Target. By keeping careful Track of the Range between the Transponder & Transmitter, the Oboe Operator in England would use the Equipment to see if the Bomber strayed from the Path of the Circle, and give the Pilot Instructions on how to regain it. While the Primary Transmitter could tell that the Aircraft was in the Circle, it was impossible to tell at what point it was. For this, the Range from the Secondary Transmitter was also measured, and a Circle drawn around it; the Bomber would be at the Point where the 2 Circles Intersected. By repeatedly doing this, the progress of the Bomber could be Tracked, and when it reached the Point where the Primary Line passed over the Target, a Coded Signal was sent alerting the Crew to drop their Bombs (they would typically also be alerted to Way-points and when the Target was near). The Path was only 35-yds (32M) wide, allowing for much greater accuracy than other Systems like Gee. The Curved Path of the Aircraft was quite evident to German Radar Operators, who came to call the System “Boomerang” after the Arc Segment left on their Displays as the Aircraft Appeared & Disappeared out of Range. Oboe’s Limitation of 1-Aircraft at a Time led to several New Systems. Among these were the Gee-H System, which used the existing Gee Equipment with Oboe-like Transmitters. Gee-H could guide about 80-Aircraft at Once.
‘The “Oboe” dispositions for Bombing Florennes and Essen. The Bombing Aircraft flies at a constant Range from the Ground Station at Trimingham [North Norfolk], taking it on an Arc. When it is at the correct Range from the Ground Station at Walmer [East Kent], the latter sends the Order for Bomb Release. The curved tracks are slightly (but exaggerated in the diagram) to the West of the Targets because the Bombs continue on a Tangent after Release.’
The most Precise Bomber Guidance System during the War was called Oboe and was used mostly by De Havilland Mosquitos of RAF Bomber Command.
- Aircraft flies at a constant Range from the Cat Station
- Bomb Release controlled by Mouse Station
- Aircraft carrys a Responder which Amplifies & Radiates Pulse received from Ground Station
- Pilot receives Dots & Dashes from Cat Station if Range is too small or too great
Professor R V Jones writes that Oboe ‘was the most precise Bombing System of the whole War.’ So precise, in fact, that they had to look into the question of the Geodetic Alignment of the Ordnance Survey with the Continent, which was based on Triangulation across the Straits of Dover. It was decided to check this by sending a small Force of Mosquitoes to Bomb the German Night-fighter Headquarters in Florennes, Belgium, in December 1942. Special permission was obtained to disclose this Target in Advance, so as to notify the Belgian Network, who would place Observers in position. The Belgians sent back precise details of the Bombing, risking their lives by actually pacing out the distances in yards! Best of all, One of the Bombs actually hit the Night-Fighter Headquarters! This and other Attacks convinced the Doubters of the Efficacy of Oboe.
This Bombing System was developed by A H Reeves & Dr F E Jones at the Telecommunications Research Establishment, Malvern. In discussion with Professor Jones, they realised that their Directional Measurements were not very good, but Range Measurements could be made very Accurately. To achieve this, Pulses were sent out from a Ground Station (Trimingham), which the Aircraft would Pick Up, Amplify, and then Return to the Ground Station (sometimes called Cat). The time that it took the Pulses to Return was then converted into Distance. In effect, the Aircraft would Fly along a Circle centred on the Ground Station. The Circle was made to go to 1-Side of the Target, as the Bombs departed Tangentially when Released from the Aircraft. Calculations depended on knowing the Height & Speed of the Aircraft, which, of course, the Pilot had to maintain dead Accurately. Maintaining this gentle Curve of the Circle was achieved by Automatic Signals sent out by the Ground Station – rather like on a Standard Beam Approach (Dots on 1-Side, Dashes on the other, and a Steady Note if Established), hence the aforementioned selection process for Pathfinder Pilots. Note that there is no Beam that the Germans could Detect, as in their own Knickebein System, which we, of course, Bent! A 2nd Ground Station (sometimes called Mouse) was needed (Walmer), which also determined the Range of the Aircraft from it, and this was used to Instruct the Aircraft when to Drop its Bombs to Hit the Target, taking the pressure off the Crew, especially if under Fire at the time. The Crew would receive Warning Signals that the Release Point was Imminent, then a long Dash to indicate the Release Point. The Button was pressed to release the Bombs or Markers immediately the Dash Signal Terminated. There were only 2-Minor Disadvantages with this Bombing System. Firstly, the Traffic-handling capacity was very limited, but as only a few Oboe Mosquitoes were needed to drop Visual Markers for the Main Bomber Force, this did not prove a problem. Secondly, the Aircraft had to Transmit a Signal which an Enemy Night-fighter could use to Home in. No problem there – the Mosquitoes easily outpaced them (probably Messerschmitt Bf.110s). When Oboe started using centimetric wavelengths, the Germans lost the Plot! (NB Revision – the shorter the Wavelength, the higher the Frequency, i.e. they are inversely proportional).
Wing Commander Tom Jefferson as Mosquito Pathfinder
Went on a course at Warboys for about 3-months. [No.1655 MTU, Warboys, from 20th June to 29th July 1944.] They could Direct the [Oboe] Transmissions Inland. We used a Practice Bombing Range on some Marshes near Grendon Underwood [Bucks], where there is now an Open Prison.’ Tom continues:
‘I believe that the White Triangle [aiming point] was about 27 yards each side. You had to keep at this until you could put all your Practice Bombs in that Triangle, from above Cloud! Which, of course, is very Accurate! The Navigator had to be of the same very high Standard. When you passed this Course, which everyone didn’t, you were very carefully checked out, so no one would ever find out what the stuff was about. It was so Secret that even some Station Commanders were not in the Picture! When you went to the Squadron, even as a Wing Commander, you’d be Tail-arse-Charlie – a new boy, right at the back! You’d go out, night after night, dropping 4,000-pound Cookies, for so long, until every time you came back, they told you that your Error was less than 100 yards and your Timing Error was less than 60 secs! The point being that, the Main Force by this time were trained to go out and Bomb the green or yellow Markers at H-Hour plus 2 minutes. Somebody else was on some other Markers. Now, if you weren’t a little bit early, the Main Force – up to 1,000 Bombers – would overshoot it all. They then either wouldn’t Bomb, or they’d come back and try to turn round against each other – absolute ruddy Chaos! If you dropped too early, by the time the Main Force had got there, the bloody things would go out! So it was absolutely essential to have a Timing Error of fewer than 60 seconds, and an Error from the Pinpoint of less than 100 yards, otherwise you’re wasting your effort. When you got back to debriefing, they didn’t say, did you get there, and what was it like? Did you actually see the Target? This was the sort of thing that they asked you in the early days. Instead, they were saying, not a bad run – you were 35 secs late, and 0.75°/40 yards from the Target, or something of this sort! I remember the time we Bombed Krupps – not the Main Works, which had been hit 1 or 2 times, but when it was absolutely essential that we Bombed the Boiler House. The Cartographers, with their great triangulation trig points, had worked out the position of the Southwest corner of the Boiler House exactly within feet!’
Understandably, Tom had to prove himself before being given responsibility for dropping Markers for the Main Force.
Tome recalls: ‘When you 1st went out, you would be dropping Cookies. When your assessed Error was very small & continually small, every time, you would be sent out on Decoy Raids. So when there was a big Night Effort, and there would be a great lot of Bombers going out to, say, Berlin, then the Lead Pathfinders would go down to Hanover, and cover it with Markers & drop Bombs & so on – and a lot of Heavy Bombers would follow & Bomb on these Markers. All the Night Fighters would belt over to there, while the rest of the Force would go on to Berlin. or Hamburg, or Kiel, or somewhere else. So you then did these Decoy Raids until you were so accurate & perfect in time that you were tasked with putting the 1st Markers down on the Main Raids. Often, after putting these down, you could use your Secondary Markers, and you would fly around, and if that Target was really damaged, you could get yourself into position for a later Wave, to move the Target to something else. So it was an extremely Interesting Business, indeed!’
‘I always had the same callsign – Freddie Orange – no matter which Aircraft, and people always knew that particular Pilot & Callsign: you never changed – it was never given to other people. When we were out over the North Sea, we were picked up by a Tracking Station at Tilly Whim, in Dorset [on the Isle of Purbeck], to an angle onto this fine Curve – invisible curve – and you had to settle down to Points A, B, C, & D, on your Instruments: absolutely spot on, within feet, you had to be. This “Beam” was narrower than a Mosquito – only 36ft wide compared with the 54-ft Span of the Mosquito! We were high, which put us frequently in what they would now call a Jetstream, with Clear Air Turbulence. You could easily be thrown out and you would have to fight your way back to it! You would go through the “Beam” a little bit, and then ease back into it, not forgetting that you are on a slightly curved path all the time. So, the thing is, for this very accurate thing to work, you’ve got to be right spot on Course, right bang on the middle of the “Beam“, and the Airspeed has got to be exactly right. Your height has got to be exactly right – within feet [no problem with modern Aircraft, but try doing this with the basic Flight Instruments of a Mosquito!]. To do this, you know, it takes a long time to get the Aircraft into that position. To hold it there, something like 15 minutes. I can tell you, it felt more like 15-yrs! Now, a lot of places would try and put you off – they knew these Aircraft came over, and they couldn’t find out how they did it. They knew you had to fly a steady & slightly Curved course – dead Level, no Jinking, no Evasive action or anything – that you had to Fly very accurately for so long. Some would try to put you off all the time – you’d get a constant stream of Flak coming around you, or near you. Others would hold their Fire. I particularly remember Dortmund – you didn’t get a single bit of Flak, or anything, until just about the time you were going to release the Marker. Then they really opened up – you got the whole lot from the Dortmund Area! The sky was absolutely dead solid. Now, if they were a few secs late, the minute you dropped your Marker you’d be down & away, pointing down so hard it isn’t true, changing course & spiralling, and doing all sorts of things. But if they happened to be a little bit early, they’d got you. I was expecting them to get me, sooner or later, because they did this all the time.’
Tom recalls the time when Sceptics needed convincing how Accurate a Bombing System Oboe could be:
‘Don Bennett [Pathfinder Ace] worked closely with the Oboe Scientists, and he tried it out himself, getting terrific results. He tried to sell it to, 1st of all, Bomber Harris, and then, through him, the Air Ministry. They said: “No! We’ve no money to waste on these foolhardy ideas and chancy things. The whole idea is ridiculous – it just can’t work!” So he said: “Look – can’t we have just one Trial? I’ll tell you what you are going to find the Germans saying afterwards!” They agreed, and he arranged to Bomb a Cemetery – I’m not sure whether it was Dusseldorf, or somewhere like this. He demolished the Cemetery! So all the Germans on their News and things were saying that that the stupid Britishers could do no more than come and Kill a lot of people who are already Dead! Ha! ha! ha! The Air Ministry was impressed – if a single Cemetery can be Targeted, then Oboe has got to be good!’
In The Bomber Command War Diaries: An Operational Reference Book, 1939-1945, by Martin Middlebrook & Chris Everitt (Viking 1985), it states that the 1st Oboe-Aimed Bombs were dropped by Sqn Ldr H E ‘Hal’ Bufton and his Navigator Flt Lt E L Ifould, of No.109 Sqdn, on 20/21st December 1942 during an Attack on a Power Station at Lutterade, a Small Town in Holland, near the German Frontier. Local reports suggest that the Bombs of the 6 Oboe Mosquitoes fell way off their Target! However, the book records regular Oboe Assisted Bombing from then on. The Raid that Tom described is clearly that carried out 2 nights later, on Christmas Eve, on the Ruhort Steel Works in Germany.
The Traitor William Joyce, known in England as ‘Lord Haw-Haw‘ by chance confirmed the Accuracy of this Raid when he announced on a routine Propaganda Broadcast that some British Aircraft had ‘broken the peace of the Christmas night and destroyed several graves in a remote Cemetery in Southern Germany.’ This was just what the TRE Scientists were waiting for, as they knew that a small Graveyard was situated just to the South of the Mosquitoes Aiming Point!
Group Captain Hal Bufton DFC, AFC was Tom’s Station Commander at Bourn until the end of the War. Of course, the best overall view of Oboe and the Pathfinder Force must be the book written by the AOC No 8 (PFF) Group – Air Vice-Marshal D C T Bennett, CB, CBE, DSO. Most people interested in the Bomber Command of WW2 will have surely read his fascinating Autobiography Pathfinder: Wartime Memories (Frederick Muller Ltd, London, 1958). Here are a few excerpts:
‘Whilst all this high-level activity was going on in connection with H2S the other Radar device, Oboe, was being quietly developed by its Inventor, Alec Harley Reeves, and his brilliant young colleague, Dr Francis E Jones. Reeves was seconded as a civilian scientist to the Telecommunications Research Establishment (TRE) to develop accurate Navigational devices – the 1st was GEE; the 2nd OBOE, using PCM-like pulses. OBOE was used in over 10,000 Allied Bombing Raids. Unlike H2S, which was done with full formality and in accordance with the normal Procedure. Oboe was developed by the Boffins on the Job at the Squadron itself, with the Test Installations being done in the Squadron‘s own Aircraft. Not only did this save time, but it also “achieved the impossible.” The adoption of the Mosquito to operate Oboe took some persuasion on AVM Bennett’s part. Both the Air Ministry & Bomber Command thought that the Mosquito was a frail wooden machine totally unsuitable for Service conditions, that its absence of Gun Turrets would cause it to be Shot down, and that it was far too small to carry the Specialist Equipment and an adequate Pathfinder Crew. AVM Bennett calmly dealt with each of these points in turn, before the Powers-That-Be played what they thought was their Ace Card:
‘They declared that the Mosquito had been tested thoroughly by the appropriate Establishments and found quite unsuitable, and indeed impossible to Fly at Night. At this, I raised an eyebrow and said that I was very sorry to hear that it was quite impossible to Fly by Night, as I had been doing so regularly during the past week and had found nothing wrong. There was a deadly Silence. – (Bennett got his Mosquito’s)’
Heavy Bomber Pilot’s Opinion
I confirm that Oboe (Radio Bombing System) was considered a dirty word! I think we did 60-Attacks and the greater bulk was at Night and if you were invited during the day to Fly a ‘Heavy Bomber’ straight & level for however long it is too long. We substituted for Squadron Leader Wakeman on a wretched Oboe and we immediately were bowled over and a week later he went on another Oboe Attack and again was bowled over. It’s a pity that the RAF, who took what in effect were the Cream of the Crews of Bomber Command in the Pathfinders and said, ‘Oh, no let them do Oboes.’ Let the ruddy Main Force do Oboes, not Pathfinders. We did primitive Formation of 12 or 20 with Oboe but please never Fly a large Aeroplane Straight & Level for 10 minutes in unfriendly circumstances – it really is nonsense and made them vulnerable to Attack.
WW2 Bombing Navigation System – GEE-H was the successor to OBOE because Oboe could only handle 1-Aeroplane in a period of 1000 Plane Bombing Raids. GEE-H could handle 8-Bombing Formations at a time. The Navigator of the Aircraft became the Operator and the Cat & Mouse became Transponders.
Gee – Introduced in 1942, Gee was a Medium Range Radar Navigation Aid using Ground Transmitters (Gee Chains) and onboard Cathode Ray Receiver.
The System, which had a Range of up to 350-miles, measured the Time delay between 2-Radio Signals sent from the Gee Chains to provide the Navigator with a Fix.
Gee Chart, Reims Chain, December 1944, 1/1000000 scale
This Lattice Chart depicts the Gee Reims Station Chain in Eastern France during the Final Months in the War in Europe. The Chart was used Operationally on a Bombing Raid as indicated by numerous Pencil Lines documenting Missions to Targets in Germany. One of these has an “IP” marked for an Initial Point to the South of Berlin. The Target appears to be Zossen, which Housed the German Army Staff Headquarters in the Spring of 1945. Air-Crews carried these Charts to determine Lines of position using a Gee Receiver & Oscilloscope. The RAF Established new Chains as the Allies Advanced Eastward after D-Day. An Operator using this Chart could determine a Fix using 2 or 3-Lines of Position within 3 or 4-mins. Gee was a Hyperbolic System that provided Short Range Navigation & Bombing Guidance over Britain, Western Europe and the Northern Mediterranean during WW2. Developed by the British Telecommunications Research Establishment (TRE) under the Technical Guidance of Robert G Dippy, the System guided larger Aircraft (Bombers, Transports, Reconnaissance Aircraft & Night Fighters) to accuracies of a Statute Mile or better at Ranges up to 400-Statute Miles. Both the RAF Bomber Command and American 8th Bomber Command depended extensively on the Technology. A Blind Bombing System called Gee-H (or GH) used the Gee Transmitters along with modified Aircraft Equipment to create a Transponder System that could Guide Bombers at Night or in Cloud to within several 100-yds of a Target.
Pathfinder Craig 