Britain’s Thermonuclear Bluff

Norman Dombey and Eric Grove

‘Britain Carries Out Second H-Test, Explosion even bigger than the first one,’ the Manchester Guardian reported on Saturday, 1 June 1957. It was the lead news item. The story that followed was datelined ‘Aboard HMS Alert’, Alert being the frigate which housed the representatives of the British press corps invited to see for themselves that Britain, as befitted the third great power in the world, had attained thermonuclear status. According to Reuters, ‘a great multi-coloured fireball above the central Pacific heralded Britain’s second hydrogen bomb test’ off the Malden Islands.

In retrospect, there are two problems with these accounts. First, the test of Orange Herald was held on Friday, 31 May: it would not have been physically possible for the story to appear before the following Monday. In other words, the journalists wrote their stories in advance of the test, on the basis of a briefing from Brigadier Jehu, who had seen the first test – Short Granite – of the 1957 Grapple series on 15 May. Secondly, it now appears very probable that Orange Herald was not an H-bomb at all, but a large A-bomb. Journalists, after all, could not be expected to differentiate between mushroom clouds, and no figures were issued then (or have been since) about the size of the test.

To this day the British Government is very reluctant to give any details about the thermonuclear programme it embarked on 38 years ago: certainly we know more about the early stages of the Soviet thermonuclear programme than we do about the British. However, three things have made it possible for us to attempt a reconstruction of events between 1954 and 1958: an unusually forthcoming obituary, in the Biographical Memoirs of the Fellows of the Royal Society, of Sir William Cook, scientific director of the Grapple test series; some recent disclosures on the part of John Ward, who was employed at the British nuclear weapons laboratory at Aldermaston for six months during 1955; and a group of declassified US documents obtained by Robert Norris of the Natural Resources Defence Council in Washington. It may well be that there are errors in our account – given the habits of secrecy and misinformation which prevail among British governments it could perhaps hardly be otherwise – but what follows is at least an introduction to the issues.

The Orange Herald test was only the most blatant example of Britain’s thermonuclear bluff: it seems that none of the four nuclear tests held in 1957 was a hydrogen bomb test as we now understand it. But the tests had as much to do with public relations, and especially relations with the United States, as with constructing an authentic hydrogen bomb, and the bluff was remarkably successful. Within four years of Churchill’s decision to launch a British H-bomb programme, Britain’s overriding political objective – a special nuclear relationship with the United States – had been achieved. That this goal was reached appears to have been due mainly to the contribution of the physicist John Ward. The closeness of the US-UK special relationship in nuclear weapons which resulted from the combination of this bluff and Ward’s genius has also been a carefully kept secret. In fact, from 1958 onwards the United States transferred to Britain detailed design drawings and material specifications of many of their most modern hydrogen bombs so that Britain could manufacture these US weapons as its own. The story we tell has its ironies: Britain’s initial reason for developing its own H-bombs was that it wanted to be in a position to influence US nuclear policy, but the US ended up with substantial power over British nuclear policy.

There are two basic methods of obtaining usable nuclear energy: fission, or the splitting up of heavy elements into lighter elements, and fusion, where light elements combine to make heavier elements. This defines the distinction between A-bombs and H-bombs: A-bombs are fission bombs where the fuel is uranium-235 or plutonium-239. H-bombs are fusion bombs where the hydrogen isotopes deuterium (hydrogen-2) and tritium (hydrogen-3) form the fuel. The reason these weapons are also called thermonuclear is that temperatures comparable to the temperature of the Sun are needed to initiate the nuclear fusion process. Both the fission and fusion processes liberate substantial amounts of energy, but while the yield of an A-bomb is characteristically measured in kilotons, that of an H-bomb can reach many megatons or millions of tons of high explosive.

Tritium is often added to fission weapons to provide some fast neutrons from thermonuclear processes in order to increase the yield of the weapon. The weapon is still referred to as a fission weapon, however, because almost all the explosive energy comes from fission, not fusion. It is worth bearing in mind that it was exceedingly difficult for the United States to develop megaton hydrogen bombs in which a significant part of the energy came from fusion. Although President Truman had authorised the H-bomb programme in 1950, calculations later that year on one of the world’s first electronic computers showed that the hydrogen bomb design on which the weapons laboratory at Los Alamos had been working since the mid-Forties was fundamentally flawed. The ‘Super’, as the early hydrogen bomb was known, would have blown itself apart before any appreciable thermonuclear processes were initiated.

Edward Teller and Stanislaw Ulam, émigré scientists from Hungary and Poland respectively, who were working at Los Alamos, found an ingenious solution in 1951. As part of his work on improved fission weapons Ulam had suggested a two-stage fission design. Teller seized on this idea and proposed a first fission stage which would set off a separate fusion stage by means of X-rays transmitted from the fission explosion. Since X-rays are a form of electromagnetic radiation they travel at the speed of light and thus can in principle implode and ignite the thermonuclear fuel before the shock wave from the primary stage blows it apart. This process is known as radiation implosion; and according to normal US nomenclature, a ‘hydrogen’ or ‘thermonuclear’ bomb refers to a weapon which incorporates the Ulam-Teller concept of two (or more) stages and radiation implosion. A prototype H-bomb, ‘Mike’, incorporating these principles was first successfully tested in November 1952 and was followed by the Castle series at Bikini between March and May 1954 in which several thermonuclear weapons with yields larger than one megaton were tested.

In August 1953 the Soviet Union exploded a large nuclear weapon, known in the West as Joe-4, which it announced was thermonuclear. US weapon scientists have known for some time, however, that the yield of Joe-4 was only about 200-300 kilotons and that it was therefore unlikely to have been a hydrogen bomb in the Ulam-Teller sense. This has recently been confirmed by Soviet physicists writing about Sakharov’s role in the project. Joe-4 was a ‘layer-cake’ device with layers of light and heavy elements. The light elements were in the form of the thermonuclear fuel lithium-6-deuteride and the heavy elements were plutonium, uranium-235 and uranium-238. The latter isotope is then fissioned by fast neutrons from the thermonuclear reaction. By far the greater part of the energy of Joe-4 still came from fission, not fusion, so we will follow US terminology by referring to such weapons as thermonuclear-boosted fission weapons rather than thermonuclear weapons or H-bombs. Such boosted fission weapons are not as efficient as two-stage radiation implosion H-bombs and would not be expected to have yields as large as one megaton.

The British decision to build a hydrogen bomb was taken by a sub-committee of the Churchill Cabinet in 1954, in the aftermath of the US Castle test series. The power of those weapons – one reached 15 megatons – seems to have come as a surprise to everyone including the weapon designers, and the British Government decided that they were too dangerous a capability to be left to the US alone. Churchill felt ‘that we could not expect to maintain our influence as a world power unless we possessed the most up-to-date nuclear weapons,’ while the Chiefs of Staff emphasised the need to have as much influence as possible over the use of the H-bomb. So the aims of British thermonuclear policy were political rather than military right from the start: prestige and a US-UK special nuclear relationship were the objectives.

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