The Warhead

The saga of the warhead is a story in itself. The urgency with which it was pursued is slightly puzzling in hindsight since it was not intended to deploy Blue Streak until the mid-1960s. The UK had taken the decision to develop thermonuclear devices (also known as fusion weapons or more popularly, the H bomb) in 1954, and the Atomic Weapons and Research Establishment (AWRE) at Aldermaston did not as yet have a working design. Given all the other development work that needed to be done, a decision on a warhead could have been deferred until a fusion weapon had been developed. There was a degree of risk in this: there was the possibility that no warhead could have been developed within the weight limit of one ton. On the other hand, the Blue Streak design was the largest possible for a single stage vehicle with only two motors. Designing anything larger would have led to a very unwieldy weapon.

What Britain did have was a relatively low yield lightweight fission device – Red Beard – and a design for a much more powerful warhead which incorporated fusion principles, but was not what would now be called a thermonuclear device. This was Green Bamboo – never tested, since it soon became obsolete. The snag was that this device had a weight in the region of 4,500 lb, but in the absence of anything else, it was Green Bamboo which was specified in OR 1142, entitled ‘Warhead for a Medium Range Ballistic Missile’.

Red Beard, the lightweight fission weapon, had been ruled out since its yield was only 10-20 kilotons (kT), and given the predicted accuracy of Blue Streak, this was thought to be inadequate. Green Bamboo was too heavy. Thus William Penney, then Director of Aldermaston, was asked if a lighter warhead of similar yield could be built. He replied to say this might be possible, but that ‘the figures of 1,800 lb weight and 30” diameter quoted for an unboosted fission bomb with a yield of about 1 megaton were purely estimates at this stage and could not be guaranteed.’4 After further study, he decided that ‘on current knowledge I could not guarantee to make a satisfactory warhead within the weight specified’. A weight of around 2,200 lb was more probable, and it would use around twice as much fissile material as Green Bamboo. It would be a pure fission device, but in the absence of any alternative, this warhead, now codenamed Orange Herald, was chosen, and, punctiliously, the wording of the OR was changed from ‘thermonuclear’ to ‘megaton’. (Note: there is some ambiguity here. ‘Megaton range’ meant around a megaton yield, and 600 kT would qualify since 600 kT = 0.6 MT, which can be rounded up to 1 MT.)

Given that the lightest warhead that AWRE could guarantee would weigh 2,200 lb, this decided the issue of one motor or two for Blue Streak: if it was to reach the range required it would need two motors.

A memo concerning Orange Herald sums up the position with some rather interesting comments along the way:

Orange Herald – OR1142

Your loose minute of 31 October asks what is the present status of the official requirement for Orange Herald, and whether the Minister knows of the project. I propose to answer in some detail for I think that it will be useful to record the history of the project.

2. A Draft Operational Requirement No. OR1139 (May 1955) for the Ballistic Missile was discussed at an Air Ministry Operational Requirements Committee meeting on 9th June, 1955. … In discussion of the range of the missile a warhead weight corresponding to Green Bamboo was assumed, and it seemed unlikely that the range which Air Staff desired could be met by a single-motor missile…

4. In the meantime, however, CGWL had been discussing with AWRE the penalties implicated on the missile design by the weight of Green Bamboo, and DAWRE [Director AWRE, William Penney] had said that he could develop a megaton warhead of about half the weight, although requiring more fissile material.

5. This smaller megaton warhead was considered by AWRE to be an important project, and in mid August I was asked by AWRE to arrange for an MOS [Ministry of Supply] code word to be registered for it, for AWRE use and to facilitate inter­departmental discussion. One copy of my minute notifying the choice of a code word for “A megaton warhead for the Medium Range Ballistic Missile” went to PS/Minister [the Minister’s Private Secretary] but, of course, without any description of the warhead

7. In discussion on 14th October, DDAWRE [Deputy Director AWRE] made it clear that AWRE consider it important to go ahead with the lighter warhead, that they are in fact doing so (for the present on their own initiative) and that they are considering the possibility of a trial in 1957. AWRE’s line is thus quite clear …

9. I have also consulted the CGWL side, in the person of DGGW [Director General Guided Weapons]. He tells me that they are not yet in a position to put up the missile requirement OR1139 for the Minister’s approval prior to acceptance: they still consider the project to be in the design study stage, and a meeting will probably be held in December (1955) to make a final assessment. It seems almost certain that a twin-motor design will be agreed, but whether the missile has one or two motors, they will still want the lighter warhead. I pointed out that Orange Herald has at the moment the status of a private venture on the part of AWRE, and that it seemed to me desirable that an OR should be issued to cover it. So far as DGGW is aware, the Minister has not been given any data from the CGWL side on the characteristics of

Orange Herald.

10. Thus the answers to your questions are:

(a) The present status of Orange Herald is that of a private venture by AWRE, for the present Air Staff Requirement for a warhead for the OR1139 missile refers specifically to Green Bamboo. DGGW will inform Air Staff that the missile needs a lighter warhead; this should result in a revised OR calling in effect for Orange Herald, and we can then clear with AWRE the warhead parts of this OR in readiness for the eventual submission of 0R1139/1142 to the Minister by CGWL and CAW [Controller Atomic Warfare].

(b) There is no evidence that the Minister knows anything of the project beyond the code word and its definition.

[Sgd] D. CAMERON DAW Plans. (10th November 1955)

That last line is worth repeating: ‘there is no evidence that the Minister knows anything of the project beyond the code word and its definition’. Decisions involving the expenditure of millions of pounds were authorised not by the politician in charge of the ministry, but by the senior officials running the projects – and Orange Herald probably cost close on ten million pounds (as much as Black Knight or Black Arrow) to design, build and test. Indeed, it is rare that ministers were involved in anything other than the basic decisions. Mention is made of the OR being subject to final ministerial approval. It would be unfair to say that this comprised a ‘rubber stamp’, but on the other hand, how was a professional politician able to judge whether the OR made sense or not? Ministers would take decisions on matters such as whether a ballistic missile was needed, and the rest was up to the permanent officials. Ministers do take the final responsibility – thus when Blue Streak was ultimately cancelled as a weapon, ministerial reputations were at stake. Indeed, it might be said that Duncan Sandys’ defence of Blue Streak while Minister of Defence and Minister of Aviation, even though it was his job to do so, probably hindered his future career. This memo does throw some light on the degree to which decisions involving very large sums of money are taken quite independently of the minister who is nominally in charge – and yet, in almost any system of government, this is the case.

Orange Herald was, in many ways, an extremely unsatisfactory device. It required a very great deal of weapons grade U235 – one Air Ministry paper gives a figure of 120 kilograms, although other figures have been quoted. Whether the UK had the facility to produce 60 such warheads is a very interesting question. Another memo noted that ‘Orange Herald is one of the rounds to be tested at Grapple next year. The cost of the material may be £2% million.’ If those costs were carried through to the final deployment, then the warhead cost would be 60 x 2% = £150 million!

Operation Grapple was a series of tests of atomic devices based at Christmas Island in the Pacific. Three devices were scheduled for the first series, held in mid-1957, and Orange Herald was the second. The first and third were attempts at fusion devices, which were not wholly successful, but showed ‘proof of principle’. Grapple had been described by the British Government as ‘H bomb’ tests, and the press reported the Orange Herald test as an ‘H bomb success’. Orange Herald was not an ‘H bomb’, but rather a large fission device, although one can understand why the Government did not draw attention to this. This has led some later commentators to suggest the deception was deliberate – that if the fusion tests had not worked then the Government could always claim success via the Orange Herald test, whose yield was around 720 kT.

Although as we will see, Orange Herald was never deployed in its original function as Blue Streak warhead, it did come into service in a rather indirect way. The fusion tests later in 1957 were successful, but there was still a long way to go between the testing of the ‘physics package’, as the part that goes bang is sometimes called, and deployment of a fully serviceable weapon with all its handling and safety devices. Mainly for political reasons, a high yield warhead was required for the V bombers so that the Government could say the RAF had a ‘megaton capability’. The answer was a reduced yield (400 kT) version of Orange Herald, codenamed Green Grass.

Initially, the warhead was mounted in the casing of the original British atom bomb, Blue Danube, and the resultant weapon named Violet Club. Owing to the large amount of fissile material (U235) in the warhead, there were some very considerable operational limitations. Any mishandling of the device which caused it to become damaged might result in sufficient fissile material coming into contact so as to cause a low level explosion. One safety device used to prevent this happening was several hundred ball bearings, which filled a void inside the warhead and physically kept the fissile material apart. If Violet Club had ever been flown operationally (which is unlikely), the ball bearings would have had to be removed before take-off. A later version was produced in a different casing (Yellow Sun Mk 1) which allowed the ball bearing to be jettisoned in flight! The number of Green Grass warheads produced was quite limited, partly due to the amount of fissile material needed, and, given the constraints with which the weapon had to be handled, the RAF was quite glad when it was replaced by a fusion warhead.

The testing of Orange Herald meant that RAE could now move on with the design of a re-entry vehicle for Blue Streak, but to do so meant that AWRE had to supply details of the warhead in terms of masses and dimensions. Little was forthcoming, until a slightly indignant memo in May 1958 from the Deputy Director at RAE noted that

… it was learned that no work was in progress on Orange Herald at AWRE, nor was there any intention of doing any. Newley suggested that our work, based on Orange Herald, should be stopped, and that AWRE would offer instead a two-stage warhead of similar weight… Orange Herald had very doubtful in-flight safety, and is highly vulnerable to R effects, and the new proposal is welcome in that it would be greatly superior in both these respects. Nevertheless, it seems to have emerged in a most casual fashion.5

The ‘R effects’ mentioned refer to a perceived vulnerability of warheads to neutron irradiation. Orange Herald, with its large amount of U235, would have been very vulnerable to such effects.

The two-stage device referred to would be some variation on the fusion weapons that had been tested at Grapple. These went under the generic code name of ‘Granite’ devices (e. g. Green Granite, Purple Granite etc.). Hence the RAE, who was responsible for the re-entry vehicle, dropped their work on Orange Herald, and waited in anticipation for details of the size, shape and weight of the new Granite devices.

There then followed one of the greater ironies of the British nuclear weapons programme. Nuclear co-operation with the United States had ceased soon after the end of the war, and Britain had gone it alone in the development of firstly a fission device and now a fusion device. In many ways, the achievement was quite remarkable, as Aldermaston, with its relatively small budget and limited resources, produced a working fusion design less than three years after work had begun. As a result of Aldermaston’s success, the Americans agreed to resume nuclear co-operation. The UK was given the designs for two nuclear warheads, one of them being the Mark 28, approximate yield 1.1 MT. The advantage to the UK was that the design had been fully engineered as a weapon rather than just as an experimental device, and so the Granite designs, painstakingly developed by Aldermaston, were dropped in favour of the Mark 28. The anglicised version of the Mark 28 would go into service as Red Snow.

The major problem to continuing with ‘weaponising’ a Granite design was that further nuclear testing would have been required, and public and world opinion was turning very much against atmospheric nuclear tests. Britain did not have an underground testing facility, and so the advantages of adopting the American design were that much greater. Hence if Blue Streak had been deployed operationally, then the warhead would have been the 1.1 MT Red Snow.

Whatever the warhead, it seemed that its weight would not come under a ton, which imposed its own restraints on the design. Thus Air Vice Marshall Satterly wrote in July 1955:

My views are that if we go for the single motor missile we shall always be in trouble over weight and range, and will find ourselves in the early 60’s [sic] still striving to catch up. Let us be bold and go for the twin motor and exploit any future saving in weight in the warhead, or anywhere else, by increasing the range. Let us then review the position in a years [sic] time, when we can put much more reliance on the small warhead and when we are due to consider parallel development of a second missile.6

Sir Steuart Mitchell, CGWL, ‘reluctantly agreed that two motors would probably be necessary to guarantee a range of 1500 nautical miles’. Dr William Cook, Deputy Director at Aldermaston, said that AWRE ‘had not realised how significant was the weight of the small warhead in reaching this decision.’ Reluctantly, given the uncertainties in the payload, it was realised that two motors would be needed to achieve the necessary range. A single motor missile would have been almost identical to the American Thor missile, but the heavier UK warhead coupled with the already limited range of Thor (1,500 miles with the US warhead) ruled out the use of Thor by the UK. This was summarised in a paper by Sir Frederick Brundrett, Chief Scientist at the Ministry of Defence, in June 1956:

The co-operation between the Americans and ourselves on this missile development is extremely good except that which is limited by United States laws governing the passage of information on atomic weapons. We have, in fact, considerably more knowledge on this subject than we are supposed to have and it is vitally important that the Americans are not made aware that we have the information that follows.

The warhead for Thor is being designed to a weight of atomic core of 1,500lb, but the weight of the warhead itself must include the metal sheathing designed to act as a heat sink. The total weight including this sheathing will be 2,600lb if the sheathing is of steel and 3,100lb if the sheathing is of copper. The comparable figures for our own design are 2,250lb, 3,600lb and 4,500lb…

What this means, however, is that if an arrangement could be made for the Americans to provide vehicles to which we could fit our heads, which is a technical possibility, the range of the American vehicle with our head would be reduced to something of the order of 1,100 miles…1

There is no doubt that the single motor design would have been simpler, cheaper, and would have taken less time to develop, but, in a sense, the Air Ministry had painted themselves into a corner. The missile had to be as big as it was to achieve a range of 2,000 miles with a megaton warhead. But no one appears either to have queried this requirement or even decided what the missile was for. Was it a deterrent? Was it actually intended as a weapon that could be used to win a war? Did it need a range of 2,000 miles? The Strath Report, also concluded in 1955, looked at the effect on the UK of just five megaton warheads, and was deeply pessimistic about the result. And if the intention was to ‘win’ a nuclear war with the USSR, how much destruction would have been necessary to annihilate it or, at least, force it to surrender?

The requirement could have been relaxed either in terms of range or warhead – and it does seem odd that no one ever contemplated the possibility of warheads becoming lighter. And given the range as 2,000 miles, why did it have to be a megaton warhead? Would 200 or 400 kT have been sufficient? And could Aldermaston have designed such a warhead within the new weight constraints? Further, the payload weight was pushed up by inadequate knowledge of the re­entry head. It might have been worth putting more research into re-entry before finalising the design. It is possible that a single motor design might have had a better chance of ultimate deployment, being smaller, cheaper and quicker into service. But the assumptions on which the criteria were based never seem to have been questioned in depth.