Having previously included the obituary to Wg. Cdr. Hubbard, and having read the article in the June edition of Aeroplane on Operation Grapple, I was tempted to make a visit to the National Archives at Kew to have a read of a few of the files.  This page has a few comments and diagrams from that visit.

Bombing training Bombing accuracy Bomb-run track

This photo shows the 49 Sqn crew of Wg Cdr K.G. Hubbard in front of Valiant XD818; the first British aircraft to drop a live thermonuclear warhead. From left to right; Co-pilot Fg Offr R.L. Beeson, Flt Lt Washbrook (nav), Hubbard, Flt Lt E.J. Hood (observer) and Flt Lt E. Laraway (signaller).  Name of dog, who knows? Photo from June edition of Aeroplane.

I will not be attempting here to give a detailed blow-for-blow account of the Grapple tests, I’m sure that has been done elsewhere.  What I will do is quote various extracts from the files to give a flavour of what went on.  I will give PRO file references in the text in case anyone is keen to follow up on the files. The whole series of files can be found by searching the National Archives Catalogue, using ‘Grapple’ as a search term. There are quite a few files. The tests involved air drops from Valiants, but they also included weapons suspended from balloons; I will only concern myself with the air drops.  As part of the rehearsal and training program at Christmas Island the crews also dropped a good number of conventional bombs to prove procedures.

As I have a reasonable amount of information from the files I will add items to the site periodically, rather than try to do it all in one ‘slam dunk’.

As might be expected with a program of this nature, a lot of people and equipment had to be moved to Christmas Island, as part of this 160 Wing was formed [PRO AIR 20/10355] as the headquarters and technical unit, while a detachment of 49 Squadron under Wg Cdr Hubbard would be the operational element. One little gem from this is the listing of equipment to be moved, among the items, to support 100 men, is the sending of an additional 50 pairs of “Drawers, short, cellular” which many of us learned to love/hate in our early service careers. Waist size 32” and 34” were the most common.  It’s amazing what lies under a “SECRET” classification! Before moving to Christmas Island 160 Wing was temporarily based at Hornchurch. There is an interesting signal outlining the accommodation that would be made available for the poor devils involved.

“Normal accommodation available for seven officers.  Sub stabdard accommodation for nine SNCOs in hutted building sharing rooms.  Sub standard accommodation available for seventy nine airmen in Homeland Emergency Accommodation with reduced bedspace without lockers and with adjacent detached ablutions. If these conditions are considered satisfactory commitment can be accepted.” The response was that this was acceptable, but I suspect the person making that decision would not be sleeping there.

One area that took a lot of attention was nuclear safety, decontamination of aircraft and crews and the analysis of the explosion by the Canberras of 76 Squadron (the ‘sniffers’).  There was also heavy involvement by Hastings aircraft for transport as well as 100 Sqn for various reconnaisance/met flights and Shackletons from 206 and 240 Squadrons for sea-search.  The program lasted a good few months as Wg Cdr Hubbard dropped his weapon on May 15, 1957 while the last flight was on September 11, 1958.  Each aircraft that went for a drop had an accompanying Valiant codenamed Grandstand. The drops made by Hubbard’s detachment had Malden Island, 365 miles south-east of Christmas Island, as the target. The later 1958 drops had a target point in the sea off the south-east corner of Christmas Island itself.

This shot from Aeroplane shows a line up of ‘sniffer’ Canberras.

This diagram shows the patterns flown by the Valiant and the ‘sniffers’ on Grapple ‘Z’, the last of the drops in September 1958.  The Boss of the Canberras is appropriately designated as ‘Sniff Boss’; well, why not. The patterns are around the GZ which is off the south-east point of Christmas Island. 

In the notes for the Grapple ‘Z’ drop the ‘sniffers’ were having to go in on their runs some 33 minutes after the drop, and at heights up to and above 50,000ft. They needed usable samples for the scientists, and runs were changed to obtain the samples, based on the readings they were seeing on the different runs.

Bombing training. [Taken from Hubbard’s report in PRO file AIR 20/10360]

The aim was to drop the weapons from 45,000ft using visual bombing techniques, the T4 bombsight, but with a couple of backups. It is interesting that there was no intention to try radar bombing using H2S; they would use the techniques used in the Suez operation.  The detachment who would go to Christmas Island was formed in late 1956 and was intended to undergo various training programs in the UK before leaving for the Pacific. Unfortunately, but not surprisingly, the UK weather had a say in the program.  There were few targets around the UK that the crews could use for live visual bombing, and those that were suitable were subject to the winter weather in the UK. As a result the crews left on ‘Grapple’ with only limited bombing training having been completed. At Malden Island the crews would be expected to drop on a visual target with 50 yard sides, painted Day-Glo red. This target would be the aiming point but there would then be a time delay before release, they called it ‘overshoot’ bombing.

Two backups were considered in the event that visual bombing would be difficult on the day, these were DECCA and a system I am not familiar with called AVOCADO.  Decca relied on the old Decca ‘chains’ and the Decca lanes marked on the Decca maps.  I vaguely remember using them on the Dominie in Nav training, but not on the Vulcan.  The problem was accuracy because the Decca stations were a considerable distance away, making it difficult to get the correct lane. They found that if Decca was to be used then they needed to reset the Decca to a known point, the target, on an overfly before doing the bomb run.  This ‘lane slip’ was giving them errors of up to 400 yards, so requiring the reset.

Avocado was a blind bombing aid on HMS Warrior which was there as part of the Grapple force. I have no idea how it worked but according to Hubbard’s report, not very well.  In their trials they compared it with visual bomb runs and found that it would give them ‘gross errors’. “It was decided that this aid should only be used as a last resort when all else failed and bombing accuracy was not a necessity”.

Bombing accuracy.

During the Grapple exercises a lot of work was done to understand the accuracy of the bombing; accuracy was necessary for the development work being done by AWRE. As mentioned above, the bombs would be dropped visually using the T4 sight, there would be HE bombs as well as live rounds. The bombing exercise required aiming for a target, but there would then be a delay of some 19-20 seconds before release. The bomb was to be dropped from 46,000ft, then after some 53.4 seconds of bomb-fall there should be a detonation at 8,000ft.  The burst height was important for AWRE measurements, but was difficult to attain. The burst height was dependent on the pilots maintaining the constant drop height, not only up to and at release, but also for the subsequent time delay. What was happeneing was that the aircraft was often climbing or descending through the drop height at the time that the 19 second delay started, so causing a height error at time of detonation.  See diagram below.  There were also other factors affecting drop height including the running time of the fuse, which did vary, and also, surprisingly, quite large variations in the weight of the round, up to +-700lb, which had a large effect.  If anyone is interested in floowing this up in detail there is a PRO report which goes into some detail; AVIA 6/17458.

The following diagrams and tables give some analysis of the accuracy of the bombing, using practice and live rounds.  The first diagram shows the ‘scatter’ for large and small practice bombs.

The table beow was drawn up in August 1957 by Hubbard and shows the bombing accuracy for 13 drops, 10 of them practice while the 3 with a ‘x’ against the date shows live rounds. They found that the 50% radial error for all of them was 403 yards.

The track flown for the drops showing decca measuring stations, recording cameras and target position.