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65th Anniversary of Operation Mosaic
by Ceri McDade
Operation Mosaic was a series of two Commonwealth nuclear tests conducted at the Montebello Islands on 16 May and 19 June 1956. The yield of the first test was 15kt, detonated on 16 May 1956 at 1150 hours. The Maralinga testing site was not yet ready, so the Montebello Islands were chosen as the perfect place to perform these two tests.
The purpose of G1 was to test the increased yield of British nuclear weapons and is set in time at the Montebello Islands three and a half years after Operation Hurricane, the first British 25-kt atom bomb test aboard the HMS Plym on 3 October 1952. The British then performed Operation Totem in October 1953, which tested a limit on the amount of plutonium-40 that could be present on a bomb. Alongside Totem, which took place at Emu Field in the Great Victoria Desert in 1953, were the Kittens trials, which didn’t focus on explosions, but experimented with the effects of conventional explosives on polonium-210, beryllium and natural uranium to investigate “neutron initiators”, which kick start a fission chain reaction. These “Minor Trials” at Emu Field became known for causing more destructive damage than the major tests a couple of years later. The British weren’t keen on returning to Emu
Field due to the sudden dust storms, sand dunes and water shortage which could hamper their time-constrained work on competing with the US to test a British hydrogen bomb.
It was clear that British scientists, under William Penney, were becoming more ambitious in their testing, focusing on output and competition with the US rather than the safety
of military personnel. The Atomic Weapons Research Establishment (AWRE) considered using boosted fission weapons, where isotopes of light elements such as lithium-6 and deuterium were added. They had heard from the American tests, that using a natural uranium tamper (uranium-238 can be used during fission to produce plutonium -235) could increase the yield from 20-50%. The Australian government had already dictated that the British were not allowed to experiment with
hydrogen bombs in Australia, so using a boosted fusion weapon, circumvented the fact that they would test a hydrogen bomb, despite it being closely linked with hydrogen bomb development.
Prime Minister Anthony Eden cabled Robert Menzies, Prime Minister of Australia, on 16 May 1955, to detail the proposed tests. Eden promised that the yield would be less than two and a half times the yield of Operation Hurricane, hence not exceeding around 60kt of TNT; later 80kt was agreed between Eden and Menzies. Eden stated that the two bombs would be detonated from towers and produce a fifth of the fallout from Operation Hurricane. He gave assurances that there would be no harm to sea life or animals and humans on mainland Australia...
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CAMPAIGN SUMMER 2021