page_title: Operation Mosaic
section_title: G1
hierarchical_section_title: Operation Mosaic / G1
caption_attribution_description: English: HMAS Warrego.
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: Adams arrived at Monte Bello on 22 April, and was sufficiently impressed with the progress of works to schedule a scientific rehearsal for 27 April. A second scientific rehearsal was held on 2 May, followed by a full dress rehearsal on 5 May. The fissile material was delivered by an RAF Hastings to Onslow, from whence it was collected by HMS Alert on 11 May, and delivered to the Monte Bello Islands the following day. Five members of the AWTSC—Leslie H. Martin, Ernest Titterton, Cecil Eddy, Butement and Dwyer—arrived at Onslow and were flown to Narvik by helicopter on 14 May. The following day, Martell set 16 May as the date for the test. There had been protests in Perth at the test series, and the Deputy Premier of Western Australia, John Tonkin, promised to discuss demands for an end to the tests. Martin and Titterton confronted Martell and Adams, and Martin told them that without sufficient information about the nature of the tests, the AWTSC could not approve the test. That it had a veto came as a surprise; it was not what their orders from London said. Penney sent a message to Adams 10 May: 
  Strongly advise not showing Safety Committee any significant weapon details, but would not object to their seeing outside of cabled ball in centre section. They could be told that fissile material is at centre of large ball of high explosive and that elaborate electronics necessary to get symmetrical squash. No details of explosives configuration or inner components must be revealed. Appreciate that the position is awkward for you and that you must make minor concessions.
  Rather than stonewall, Adams and Martell disclosed the same information that had been given to Menzies, on condition that they kept it to themselves. This mollified them, and the G1 test went ahead. The device was detonated on Trimouille Island at 03:50 UTC (11:50 local time) on 16 May. Soon afterwards, Narvik and Alert entered the Parting Pool in the Monte Bello Islands. The Radiological Group, wearing full protective clothing, entered the lagoon in a cutter. They retrieved measuring instruments and conducted a ground survey. A tent with a decontamination area was established ashore, and a water pump allowed the Radiological Group to wash themselves before they returned to Narvik. The main danger to the ships' crews was considered to be from radioactive seaweed, so they were prohibited from catching or eating fish, and the ships' evaporators were not run. Spot checks were made to verify that there was no contamination on board. Most of the sample collection was completed by 20 May. An extra run was made to collect film badges from Hermite Island, and Maddock paid the crater a visit on 25 May to collect further samples. Two RAF Canberra bombers flew through the cloud to collect samples, one of which was flown by Menaul.
  The results of the test were mixed. The yield was between 15 and 20 kilotonnes of TNT (63 and 84 TJ), as had been anticipated, although the mushroom cloud rose to 21,000 feet (6,400 m) instead of 14,000 feet (4,300 m) as predicted. Valuable data was obtained. The implosion system had performed flawlessly, but the boosting effect of the lithium deuteride had been negligible; the process had not been fully understood.  HMS Diana, about 6 miles (9.7 km) from ground zero, was quickly decontaminated, and sailed for Singapore on 18 May. The fallout cloud initially moved out to sea as predicted, but then reversed direction and drifted across northern Australia. Tests on the aircraft at Onslow had detected signs of radioactive contamination from G1, indicating that some fallout had been blown over the mainland.
caption: The sloop HMAS Warrego carried out a hydrographic survey of the Monte Bello Islands
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