Operation Mosaic
Operation Mosaic was a series of two British nuclear tests, called G1 and G2, conducted in the Montebello Islands in Western Australia on 16 May and 19 June 1956. These tests followed the Operation Totem series and preceded the Operation Buffalo series. The second test in the series, G2, remains the largest ever conducted in Australia.
The purpose of the tests was to explore increasing the yield of British nuclear weapons through boosting with lithium-6 and deuterium, and the use of a natural uranium tamper. Although a boosted fission weapon is not a hydrogen bomb, which the British Government had agreed would not be tested in Australia, the tests were connected with the British hydrogen bomb programme. The Operation Totem tests of 1953 had been carried out at Emu Field in South Australia, but Emu Field was considered unsuitable for Operation Mosaic. A new, permanent test site was being prepared at Maralinga in South Australia, but would not be ready until September 1956. It was decided that the best option was to return to the Montebello Islands, where Operation Hurricane had been conducted in 1952.
To allow the task force flagship, the tank landing ship, to return to the UK and refit in time for Operation Grapple, the planned first test of a British hydrogen bomb, the terminal date for Operation Mosaic was set as 15 July. The British Government was anxious that Grapple should take place before a proposed moratorium on nuclear testing came into effect. The second test was therefore conducted under time pressure. During the Royal Commission into British nuclear tests in Australia it was claimed that the second test was of a significantly higher yield than suggested by the official figures: as compared to, but this is unsubstantiated.
Background
Early in the Second World War, Britain had a nuclear weapons project, code-named Tube Alloys. The 1943 Quebec Agreement merged it with the American Manhattan Project to create a combined American, British, and Canadian undertaking. After the war, the British Government expected that the United States would continue to share nuclear technology, which Britain regarded as a joint discovery, but the United States Atomic Energy Act of 1946 ended technical cooperation. Fearing a resurgence of United States isolationism, and of Britain's losing its great power status, the British Government restarted its own development effort, which was given the cover name "High Explosive Research". The first British atomic bomb was tested in Operation Hurricane at the Montebello Islands in Western Australia on 3 October 1952.Britain thereby became the third nuclear power, after the United States and the Soviet Union but, just four weeks after Operation Hurricane, the United States successfully tested a hydrogen bomb. The technology mastered in Operation Hurricane was six years old and, with the hydrogen bomb in hand, the US Congress saw no benefit in renewing cooperation with the UK. Although Britain strove for independence, at the same time it sought interdependence, in the form of a renewal of the nuclear Special Relationship with the United States. Therefore, on 27 July 1954, the British Government resolved to initiate a British hydrogen bomb programme. Simultaneously, momentum was gathering, both domestically and internationally, for a moratorium on nuclear testing. The British Government was anxious that this should not occur before Britain had developed a hydrogen bomb, which it expected to achieve in 1957.
Purpose and site selection
In contemplating thermonuclear designs, the British scientists at the Atomic Weapons Research Establishment at Aldermaston considered boosted fission weapons. This is a type of nuclear device in which isotopes of light elements, such as lithium-6 and deuterium, are added. The resulting nuclear fusion reactions produce neutrons, increasing the rate of fission and therefore the yield. The British had no practical experience with boosting, so a test of the concept was required. The scientists had also heard a rumour from American sources that the yield could be improved by up to 50 per cent through the use of a natural uranium tamper. Two tests were therefore scheduled: one with a lead tamper to investigate the effect of lithium deuteride, and one with a natural uranium one to investigate effect of the tamper. It was hoped that the two tests would facilitate the development of a British hydrogen bomb.The need for speed dictated the location. The Operation Totem tests of 1953 had been carried out at Emu Field in South Australia, but that location was considered unsuitable. It was too isolated, with the nearest road over away, and only tracked vehicles, or those with special tyres, could traverse the intervening sand dunes. Emu Field therefore relied on air transport, but dust storms were a problem. Moreover, a shortage of water severely limited the number of personnel at the site. A new, permanent test site was being prepared at Maralinga in South Australia, but it would not be ready until September 1956, and the Operation Buffalo tests were already scheduled to be held there. So it was decided that the best option was to return to the Montebello Islands, where the operation could be supported by the Royal Navy. There were also doubts as to whether the Australian Government would allow a test at Maralinga.
That was a sensitive matter, because there was an agreement with Australia that no thermonuclear testing would be carried out there. The Australian minister for supply, Howard Beale, responding to rumours reported in the newspapers, asserted that "the Federal Government has no intention of allowing any hydrogen bomb tests to take place in Australia. Nor has it any intention of allowing any experiments connected with hydrogen bomb tests to take place here." Although a boosted fusion weapon is not a hydrogen bomb, the tests were indeed connected with the development of a hydrogen bomb.
The prime minister of the United Kingdom, Sir Anthony Eden, cabled the prime minister of Australia, Robert Menzies, on 16 May 1955. Eden detailed the nature and purpose of the tests. He explained that the experiments would include the addition of light elements as a boost, but promised that the yield of neither test would exceed two and a half times that of the Operation Hurricane test. Neither the anticipated nor the actual yield of the Hurricane test had been officially disclosed to Australian officials, but the yield was, so that implied an upper limit was about. Later an limit was agreed to. Eden informed Menzies that the two shots would be from towers, which would produce a fifth of the fallout of that of Operation Hurricane, and there would be no danger to people or animals on the mainland. He explained that the use of the Montebello Islands would save as much as six months of development time. Menzies wrote to Eden on 20 June and gave his approval for the tests.
Preparations
Like Operation Hurricane before it, the test was a Royal Navy responsibility. Planning commenced in February 1955 under the codename Operation Giraffe. In June 1955, the Admiralty adopted the codename Operation Mosaic. The Atomic Trials Executive in London, chaired by Lieutenant General Sir Frederick Morgan, had already begun planning Operation Buffalo. It assumed responsibility for Operation Mosaic as well, sitting as the Mosaic Executive or Buffalo Executive as appropriate. Captain Hugh Martell was in charge as commander Task Force 308, with the temporary rank of commodore. Charles Adams, from Aldermaston, who had been the deputy technical director to Leonard Tyte for Operation Hurricane, and to William Penney on Operation Totem, was appointed the scientific director for Operation Mosaic, with Ieuan Maddock as the scientific superintendent. Group Captain S. W. B. Menaul would command the Air Task Group. Planning was conducted at Aldermaston.On 18 July 1955, a five-man mission, headed by Martell, that included Adams, Menaul and Lieutenant Commanders A. K. Dodds and R. R. Fotheringham, departed the UK for Australia. They arrived on 22 July, and began a series of discussions. The Australian Government created a Montebello Working Party as a subcommittee of the Maralinga Committee, a counterpart to the British Mosex. Adams met with W. A. S. Butement of the recently formed Atomic Weapons Tests Safety Committee, an organisation created by the Australian Government to oversee the safety of nuclear tests. Mosex agreed that at least two members of the AWTSC would be present on board the Task Force 308 flagship, the Landing Ship, Tank,, when the decision to fire was taken. He also had discussions with Leonard Dwyer, the Director of the Australian Bureau of Meteorology, about the weather conditions that could be expected for the test. It was agreed that a Royal Australian Navy frigate would act as a weather ship for the test series, and that a second weather ship might be required to give warnings of willy willies and cyclones.
A small fleet of ships was assembled for Operation Mosaic. Narvik began a refit at HM Dockyard, Chatham, in July 1955, which was completed by November. She departed the UK on 29 December 1955, and travelled via the Suez Canal, reaching Fremantle on 23 February 1956. The frigate, normally the yacht of the Commander-in-Chief, Far East Fleet, was loaned to act as an accommodation ship for scientists and VIPs. Along with the tanker, they formed Task Group 308.1. The Far East Fleet also supplied the cruiser, and destroyers,, and. These formed Task Group 308.3, which was mainly responsible for weather reporting. The destroyer was detailed to carry out scientific tests, and formed Task Group 308.4.
They were augmented by RAN vessels, designated Task Group 308.2. The sloop and boom defence vessel carried out a hydrographic survey of the Montebello Islands, laying marker buoys for moorings. Care had to be taken with that, because Operation Hurricane had left some parts of the islands dangerously radioactive. The corvettes and provided logistical support, ferried personnel between the islands and the mainland, and accommodated 14 Australian and British media representatives during the first test. They were replaced by Karangi for the second test. A pair of RAN motor lighters, MWL251 and MRL252, provided water and refrigeration respectively. The two barges were visited by the First Sea Lord, Admiral Lord Mountbatten, and Lady Mountbatten, who flew out to the islands on a Whirlwind helicopter on 15 April.
Only a small party of Royal Engineers, along with two Aldermaston scientists, travelled on Narvik. The main scientific party left London by air on 1 April. The Air Task Group consisted of 107 officers and 407 other ranks. Most were based at Pearce near Perth and Onslow in the Pilbara region, although four Royal Air Force Shackletons and about 70 RAF personnel were based at RAAF Base Darwin, from whence the Shackletons daily flew weather reconnaissance flights, commencing on 2 March. Three Royal Australian Air Force Neptunes flew safety patrols, five RAF Varsity aircraft tracked clouds and flew on low-level radiological survey missions, five RAF Canberra bombers were tasked with collecting radioactive samples, four RAF Hastings aircraft flew between the UK and Australia, and two Whirlwind helicopters provided a taxi service. The United States Air Force provided a pair of C-118 Liftmasters to collect radioactive samples. The USAF wanted to monitor the British tests with their own aircraft to practice their techniques for monitoring Soviet ones. The British readily agreed, as it would demonstrate their nuclear capabilities to the Americans. Lieutenant-Colonel R. N. B. Holmes was in charge of the Royal Engineers, whose task including erecting the aluminium towers for the shots.