page_title: Operation Mosaic
section_title: G2
hierarchical_section_title: Operation Mosaic / G2
caption_attribution_description: English: HMAS Junee.
context_page_description: Operation Mosaic was a series of two British nuclear tests conducted in the Monte Bello 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 was 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 it was considered unsuitable. 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 Monte Bello Islands, where Operation Hurricane had been conducted in 1952.
context_section_description: The results of G1 meant that a natural uranium tamper could be used in G2 without exceeding the planned 80 kilotonnes of TNT (330 TJ) limit agreed to with the AWTSC. (One of 100 kilotonnes of TNT (420 TJ) was used for safety purposes.)  Scientific rehearsals for G2 were held on 28 and 31 May, followed by a full rehearsal on 4 June. The fissile core for the device was delivered to Onslow by RAF Hastings on 6 June, and once again was couriered to the  Monte Bello Islands by HMS Alert. Then followed a period of waiting for suitable weather conditions. The idea was to avoid, as far as possible, fallout being blown over the mainland. At this time of year winds at low altitudes were mainly subject to coastal influences, but above 10,000 feet (3,000 m) the prevailing winds were from the west. What was required was an interval during which the prevailing wind pattern was interrupted.
  These were not common at this time of the year; at the start of Operation Mosaic, it had been estimated that conditions favourable for G2 would occur only three days per month. In fact, since Narvik had arrived in March, not a single day had been suitable. And good weather conditions alone were insufficient; the meteorologists had to accurately forecast them. To allow Narvik to return to the UK and refit for Operation Grapple, the first test of a British hydrogen bomb, 15 July was set as the terminal date for Mosaic. As the deadline approached, William Cook, the scientist in charge of the hydrogen bomb project at Aldermaston, determined that in view of the results of G1, G2 was now more important than ever. He agreed that, if necessary, Grapple, could be delayed in order to conduct G2. With time running short, the test procedures were altered to allow for a break in the weather to be exploited, with an earlier firing time and a shorter countdown.
  Another complication was safety. While the test of a larger device would normally mandate a larger safety area, Beale announced that G2 was going to be smaller than G1. To avoid embarrassing him, the safety area was not enlarged, and no official announcement was made to the contrary. The weather improved on 8 June, and Martell ordered the countdown to begin the following day, but Beale objected to a test being carried out on a Sunday. During Operation Totem there was an agreement that no tests would be conducted on Sundays. Mosex considered that matter in London, and directed Martell not to test on 10 June. The following 48 hours were unsuitable. On 17 June the meteorologists predicted a break in the weather and Martell ordered the countdown to recommence. Weather balloons indicated that conditions were stable between 5,000 and 24,500 feet (1,500 and 7,500 m), with an anomaly between 19,000 and 24,500 feet (5,800 and 7,500 m) that was not considered significant.
  G2 was detonated from a tower on Alpha Island at 02:14 UTC (10:14 local time) on 19 June. It produced a yield of 60 kilotonnes of TNT (250 TJ), making it the largest nuclear device ever detonated in Australia. At the time of the Royal Commission into British nuclear tests in Australia in 1985, Joan Smith, a British investigative journalist, published a book, Clouds of Deceit: Deadly Legacy of Britain's Bomb Tests, in which she alleged that the G2 test had a significantly higher yield than suggested by available figures—98 kilotonnes of TNT (410 TJ) as compared to the official figure of 60 kilotonnes of TNT (250 TJ). She based this claim on "secret documents released to the Public Record Office in 1985", but the text was uncited, and the documents have never been found. British official historian Lorna Arnold reported that she had never seen any such documents.
  The cloud rose to 47,000 feet (14,000 m), considerably higher than the predicted 37,000 feet (11,000 m). The procedure for collecting samples was far more limited than that of G1. A Land Rover was landed from a Landing Craft Assault (LCA) and driven by a party wearing protective clothing  to within 400 feet (120 m) of ground zero to collect samples and recover the blast measurement equipment. 
caption: The corvette HMAS Junee provided logistical support
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