A GH Leader aircraft of No.218 (Gold Coast) Squadron

The introduction and operational use of Gee-H or GH within No.3 Group was not a simple one. It was from the very start considered by some a poor alternative to OBOE and as such its early days were one of disagreement and debate.

The first 3 Group squadron equipped was No.115 Squadron based at RAF Little Snoring. Commanded by Wing Commander F Rainsford the squadron was at the time one of the groups longest serving  squadrons with a pedigree going back to 1937. Following on 115’s heels was No.408 and No.426 RCAF Squadrons both of No.6 RCAF Group. All three squadrons were equipped with the Hercules powered Lancaster Mk.II.   No.115 Squadron started to receive its first GH sets in late August, the squadron  immediately implemented  a training programme referred  to in the ORB as “RDF Training” .  Both 115 and 406  Squadrons did not long to develop and train, they would be required  for operations  with GH by October 1st 1943, and No.426 by October 4th 1943. A fourth squadron was scheduled to be equipped, this was No.514 Squadron a recently formed Lancaster Mk.II squadron in No.3 Group commanded by ex 218 flight commander Wing Commander A J Sampson DFC.   Apart from the heavies, the D H Mosquito equipped No.139 Squadron of No.8 PFF Group was also partially equipped and being used for operational trails. With the heavies working-up Bomber Command HQ set the date for the operational debut of G-H, October 5th 1943. It would be the Pathfinders who opened the batting. One Mosquito skippered by Squadron Leader D Skene in Mosquito IV DZ601 attacked Aachen, however the raid was not a success. Problems with the frequency’s and a weak pulse resulted in the bomb load being dropped on Gee and DR.  A follow up raid was planned for October 7th, once again S/Ldr D Skene and his navigator W/O E Shipley were aloft in DZ601, the target on this occasion was Aachen. A good run onto target was achieved and the bomb load dropped successfully on G-H. A far more ambitious operation to Dortmund was planned on the 16th, nine Mosquitos of No.139 Squadron were to add the  “finishing touches to the tottering moral of the citizen of Dortmund”  (quote, No.139 Squadron ORB)

Flying Officer T Mitchell in Mosquito Mk.IV DZ601 was to drop a TI Marker over the target using G-H while F/Sgt J Marshallsay (DZ612) and F/Sgt L Simpson (DZ385) were back up with a green TI. Sadly the G-H equipment failed.  The crews for their troubles  received a rather hostile reception over the target area.

These early raids were not encouraging but confidence in the device was still high when the first heavy raid was planned. The target was the Mannesmannrohren werkes situated on the outskirts of Dusseldorf, the date was November 3/4th 1943. Thirty-eight aircraft were drawn from 115-514-408-428 Squadrons, of the 38 sets, 16 failed to work, 5 crews were forced to return early and 2 crews failed to return.  The remaining crews did themselves and G-H proud, reports from Dusseldorf records “several assemble halls burnt out”.  No.115 Squadron briefed 12 crews while No.514 briefed 2, one crew of No.115 failed to take off, of the remaining crews from 115 only Pilot Officers N Newton DS764-A and L Halley DS664-X and Flight Sergeants C James DS667-S and G Hammond DS620-V reported using their “special equipment”.  On 514 Squadron only Flight Sergeant G Hughes DS785-D reported attacking the factory.


Bomber Commands ORS Report on the attack on Dusseldorf.


GH Bomb plot for the attack on Dusseldorf November 3rd 1943.

The success was however short lived, as G-H was to be gradually withdrawn on the orders of Air Marshall Sir Arthur Harris. A memo dated November 29th from the S.A.S.O suggested rather prematurely that due to G-H’s limited blind-bombing use to date and the relatively few sets available they could be used solely as a navigational aid.  Thankfully the  idea was quickly rejected on the grounds that if the device was captured intact it could give the Germans a premature insight into its full potential allowing them to create a counter-measure and thus thwarting it’s true potential from the outset.

In December 1943 two further squadrons were scheduled to be equipped, No.218 (Gold Coast) Squadron and No.214 (FMS) Squadron.  Both were equipped with the Short Stirling Mk.III and operational from RAF Downham Market, Norfolk making it from a logistically perspective ideal. The latter would never be equipped and would within a few months be transferred to the No.100 RCM Group.   By mid December 1943, 116 G-H sets were available, 64 sets were installed between No.115-514-408 and 428 Squadrons. Twenty sets were held by No.139 Squadron and a further twenty sent to and held by No.218 Squadron, Bomber Command held a further fifteen in reserve.   

No further provisions of sets were foreseen in late December 1943, its operational usefulness was still in the balance. A full evaluation of its future was requested by HQ Bomber Command. On conclusion of the evaluation it was the S.A.S.O opinion that it was impractical to keep all four Lancaster squadrons equipped and operational and set out three proposals. These were:

(a)   Leave things as they were, train no further crews for the Lanc II squadrons and allow the gradual wastage of crews and sets to continue

(b)   Reduce to two Lanc II squadrons and maintain them up to strength, putting surplus sets into command reserve.

(c)    Withdraw GH from all Lanc II entirely and use all sets for keeping the Stirling squadrons fully operational.

The use of G-H by the RCAF squadron was to be quickly scaled down, No.6 Group would not be equipped again and their sets would eventually be passed onto No.218 Squadron.  The sets held by No.115 & No.514 would slowly be removed and either sent to 218 Squadron or added to command reserve, some would be lost before removal as the Berlin campaign reached its deadly climax.  By early January 1944 No.218 Squadron was almost fully equipped with G-H and had 100% replacements sets, it would be No.218 (Gold Coast) Squadron  that would continue with, and develop  G-H into the spring and early summer of 1944 from its new base RAF Woolfox Lodge, Rutland.  By February 1944 the AOC 8 Group AVM Bennett had decided that 8 Group would not persevere with G-H, the bitter war of words between 3 & 8 Group may have been a contributing factor, 8 Group would put all their efforts into OBOE and developing H2S.  

On April 13th 1944 No.218 Squadrons role and future was decided in a Top Secret memorandum  from HQ Bomber Command to HQ No.3 Group.  The squadron would remain part of No.3 Group and not as originally suggested by the AoC of 8 Group Don Bennett be under operational control by No.8 Group. Bennett had argued that if 218 Squadron was used to mark targets then it should be answerable to him and 8 Group HQ. Bennett had requested that PFF HQ had full operational control of the squadrons marking operations.  After a rather bitter war of words between both camps and HQ Bomber Command a decision was finally made and as such regardless of  Bennetts insistence No.218  would mark targets for No.3 Group independently and when necessary with No.8 Group.

Role of 218

No.218 Squadrons future role. This memo would result in a bitter war of words between No.3 Group and No.8 Group PFF.

The squadron would initially use G-H to assist their high level precision mine laying operations. The device was still at this late stage under trial and top secret. Any losses it was calculated would likely not result in the device falling into German hands.  No.218 Squadron continued to iron out the many operational problems with G-H, the hard work and experience gained during this period was starting to obtain results. A number of noticeable successes were achieved, Vilvorde Signal Depot on April 23rd followed by an attack on the Chambly Railway Depot on the 24th April and again on May 1st.  A post raid assessment of the Chambly raid of May 1st concluded that the bomb-plots of 7 crews were within 300 yards of the aiming point, 3 within 600 yards of the aiming point, and two within 2550 yards ( one a/c had to swerve to avoid a collision). The assessment for Vilvorde was 50% of the bomb-loads fell within 500 yards. It was later established that there was an error at the tracking station at Worth, when recalibrated the average error would have much better than 500 yards.  The two former targets were attacked in squadron strength, damage was in the scheme of things meniscal however the raids proved that if G-H worked, accuracy was as good as the proven OBOE.  


The accuracy of GH against the railway yard at Chambly is evident.

By July 1944 bombing results obtained by No.218 Squadron had improved by such an extent that the Deputy-Commander-in-Chief Saundby sent a memo dated July 2nd to the C-in-C explaining that there was now little to choose between the accuracy of G-H and its rival OBOE. Saundby also pointed out that unlike OBOE G-H could be used above cloud and no markers we required, an important factor that would be used to good effect during the weeks and months ahead.  Saundby asked approval for one group to be totally equipped with G-H, given that 218 Squadron was equipped and part of No.3 Group Saundby requested that this group should be No.3 Group. On July 3rd the C-in-C in his own hand writing replied, “Agreed, I spoke with Renwick about it and he can do it”  

By August No.218 Squadron had converted to the Avro Lancaster and moved from RAF Woolfox Lodge  to RAF Methwold. By August 21st 14 of its Lancaster’s were equipped and 31 crews fully trained. No.514 Squadron who had pioneered G-H back in 1943 was once in the process of being re-equipped.

By October 1944 No.3 Group was in a position carry out its first independent G-H operation, the target chosen was Bonn. The date was October 18th.  One hundred and twenty nine Avro Lancaster’s were detailed, forty-three of which were G-H equipped.  The G-H equipped aircraft or G-H Leaders were identified by two horizontal yellow stripes/ bars (some squadrons initially had white but this was quickly phased out) on the rudders. Non G-H aircraft would format on a predetermined Leader in a vic formation of 3 stepped down in height for bombing from 17,500ft to 16,500ft in three separate height bands.  Once behind their allotted Leader the non G-H crews followed them to the target and drop their bomb loads visual (daylight only) when the G-H leader dropped.

H-Hour was set for 11.00 B.S.T, six minutes was allotted for bombing..  Weather conditions were clearer than expected as the crews approached the target. Only 20 of the 42 bombed using G-H ( 1 failed to take-off) the remainder bombing visually due to the release pulse not be received between 10.50hrs and 10.58hrs giving crews just two minutes before bomb release. Crews frantically weaved  in an effort to pick up the pulse. The stations used was FLORENNES for tracking and COMMERCY for releasing.

Defences were moderate, but accurate especially the heavy flak which damaged 25 aircraft on the run up. This was the largest percentage of damage caused by flak the group had ever encountered on a single raid.  It was estimated that an area of 1700 yards x 600 yards of the city was completely burnt out while district of Beuel had received severe HE and fire damage.


A new policy for a new type of Operation.

No.3 Group post raid assessment found the results rather disappointing in that only 50% of the aircraft used their G-H equipment. However this 50% achieved a good concentration of bombing in the town itself, although a large proportion of the bombs fell wide of the mark. 3 Group HQ quickly evaluated the raid and pin-pointed a number of issues, crews arrived on target to early due to unexpectedly strong winds and crews opened up when encountering heavy flak. ( Daylight operations were still rather new ) Formation flying was also reported as  not good and crews especially G-H Leaders carried out a series of  S turns in an effort to stay on the tracking pulse.  However all things considered it had been a successful first operation. Over the coming months the group would put the lessons learnt to devastating effect on Germany’s synthetic oil plants, railways and industrial complexes, the vast majority of which were attacked in daylight. The group unlike No.5 & No.8 Group was not weather dependent and did not need to see the target. With increasing operational demands placed on the group accuracy and reliability of GH increased to such an extent that on occasions just sixty Lancaster’s were dispatched to individual factories with devastating results.  ( Read Sir Arthur Harris account of the introduction of GH HERE)

lanc box formation x 3

The standard Vic formation


Twin Range Systems

In the preceding paragraphs we have seen that systems based on the range difference principle become inaccurate in proportion to the square of the range; to balance this drawback they h~wc the great advantage of not being subject to saturation effects. However, for purposes such as blind bombing at great range a much more accurate system is required and this was achieved by adopting the twin range or ‘H’ principle. The position of the aircraft is determined by measuring its range from two ground beacons. The accuracy of measurement of range depends simply on the accuracy of pulse aligning and on the accuracy of the calibrator and is independent of range. The accuracy of fix, however, will depend on the angle at which the two range vectors intersect, being greatest when they intersect at right angles. It will therefore follow that with a fixed distance between the ground beacons the accuracy of fix will de-crease with range. It can be shown that this decrease in accuracy depends in a linear manner on the range whereas in hyperbolic systems, as we have seen, the accuracy decreases according to the square of the range. As an example, if the ground beacons be 100 miles apart the fix will be accurate to within about 50 yards at ranges of 100 miles, 100 yards at 200 miles and 150 yards at 300 miles. For a longer baseline the range at which a given accuracy is obtained will increase in proportion.


The method of range measurement is for the aircraft to emit a series of pulses which cause ground beacons to transmit a corresponding series of pulses. The delay between the emission of a pulse and the reception of the transponded pulse from the ground, making due allowance for the delay which occurs between the interrogation of the beacon and the transmission of its response, is directly proportional to the range of the aircraft from the beacon. The first H systems used the standard Gee indicator and the time delays were measured using the Gee calibrator. For this reason the system became known as G.H.

The transmitters in the aircraft operated in the 20 – 80 Mc /s band and used a pulse recurrence frequency in the neighbourhood of 100 c /s. In order that an aircraft might be able to identify the responses to its own transmissions its pulse recurrence frequency was ‘jittered’ automatically. As the time-base of the indicator unit is controlled by the pulse recurrence generator, only responses with the same ‘jitter’ in their frequency of recurrence will appear stationary on the screen. It will be appreciated that the beacons may be interrogated by many aircraft at one time and some such device as that just described was necessary to prevent confusion.

The time taken by the beacon to receive a pulse, send out the response arid return to the receiving condition, was about 100 microseconds. With a pulse recurrence frequency of 100 c/s a beacon would be busy for 10,000 microseconds in any one second dealing with the enquiries of one aircraft. It would therefore have 990,000 microseconds free in each second in which to respond to other aircraft, giving a theoretical maximum handling capacity of 100 aircraft. In practice of course the aircraft cannot be expected so to phase their pulses as to make the best possible use of the beacons and a handling capacity of 70 to 80 was all that was normally realized.

For blind bombing the aircraft was caused to fly on a course of constant range from one of the beacons, which passed over the target. The release point is reached when the range from the second beacon becomes equal to a previously calculated value.  The link is to YouTube and give an American view on the use of G-H by the US 8th Air Force.