Best we Forget? Perpetuating the cover up of the June 1956 Fallout from Mosaic G2 on the Monte Bellos to the Pilbara

Fig 1 DEFE 16/213 UK National Archives

Sue Rabbitt Roff

In October 1955 the Director of British Atomic and Thermonuclear tests in Australia, Professor William Penney, wrote to the Chair of the United Kingdom Atomic Energy Authority about the two detonations that were planned for the Monte Bello Islands in May and June 1956:

‘Yesterday I think I gave you the impression that the second shot at Montebello will be about 80 K.T. [kilotons]. This is the figure to which we are working as far as health and safety are concerned. We do not know exactly what the yield is going to be because the assembly is very different from anything we have tried before. We expect that yield will be 40 or 50, but it might just go up to 80 which is the safe upper limit.’ [emphasis added]

In fact in recent years it is  been listed on the website of ARPANSA [the Australian Radiation Protection and Nuclear Safety Agency] as  98 kt – more than all the other detonations in Australia up to the opening of the Olympic Games downwind of the test sites in November 1956. More than six times the detonation over Hiroshima in August 1945.

Fig 2

I recently I got an email from John Weiland whose father had been the policeman at Roebourne in 1956 when the British detonated two bombs at the Monte Bello Islands in its development of the thermonuclear weapons that were fired in the Grapple series off Christmas Island in the Pacific a year later.

John wrote:

‘I was at Roebourne in 1956; I was 7 years old. I was at school and remember hearing and feeling the blast before going outside to see the cloud. My mother said she remembers material falling on her. I was in primary school at the time and we all stood out on the verandah to watch the cloud. Also got to see my first helicopter a large yellow one which landed at the local airport. I take it that it was involved with monitoring the fallout.

My mother said at the time we had some fallout come down on the town but I find no reference to Roebourne mentioned anywhere. I have written a couple of times to various people asking if any testing was done or any follow up done particularly with the 30 or so children of the school. But I was told there was no radiation blown across from the islands. My father was the policeman in charge at Roebourne.’  But I was told there was no radiation blown across from the islands. My father was the policeman in charge at Roebourne.’  (emphases added)

 Fig 3 Photo of the Police Station was John Weiland’s home at the time of the testing / WA Library

 Fig 5 The headmaster his wife and the children of the aboriginal school. West Australia Library

At the Roebourne school (2 classrooms covering infants to high school) we got our milk in tins (Carnation evaporated milk) which we mixed with water from our rainwater tanks which was also our daily drinking water. Segregation was a thing then.

Unfortunately I don’t have a school photo of my lot but I think there were about twenty or so of us. But all of us were there in 1956 and less than 100 miles away.

I must say scholarly pursuits was not my forte but ended up tutoring Graphic Art & Design at Waiariki Institute of Technology for 18 years in Rotorua NZ. I left school to work in the sign industry gaining enough experience that was recognized by the educational authorities as equivalent to a degree although I had to do my tutor training units at the Auckland Uni. All of which I enjoyed very much. But here I am having now lived in England for 19 years retired. I worked for 11 years as a Butler and there is another story. I buttled 11 years for the Lady Pamela (Hicks) Mountbatten.

In these digital days it is possible to access the various media in which the issues Mr Weiland raises have been discussed.

The Newspaper Reports June 1956

On June 20, 1956 the Canberra Times reported on its front page

‘Spectacular Blast at Monte Bellos’:

‘PERTH, Tuesday— Onslow residents considered the atomic explosion today the most spectacular of all three so far held at the Monte Bello Islands.The shock jolted buildings in Onslow and the blast was felt at Port Hedland, 265 miles away, as three distinct ground tremors were accompanied by loud overhead report and rumbling similar to thunder.

The first shock at Port Hedland was felt 17 minutes after the bomb exploded and the second and third waves came at two minute intervals. The atomic cloud was seen for the first time at Port Hedland. It was plainly visible, reaching high above the horizon against a bright blue background.

It assumed the shape of a “blacksmith’s anvil” with a flat, top and the horn pointing to the north.The top of the cloud levelled off at about 20,000ft. (about four miles). To those people standing on Onslow jetty, the explosion was bigger than the May [first Mosaic G1] flash. The cloud appeared over the horizon about 10 seconds after the blast. The May explosion took about 20 seconds for the cloud to show. The cloud came up like a giant ice cream cone, at 10.17 (local time) the cloud was like a double mushroom. Then it was like a woman with a turned-up nose and bobbed hair, still attached to the ground by an elongated neck.  By 10.18 the top had formed into a cauliflower like a lone cumulus numbus (sic) thunderhead above the horizon. When the cloud first appeared it was darkish orange-grey and to watchers on Onslow jetty it had  none of the colours shown by the previous cloud.’ (emphases added)

Fig 6 – in public domain

Mosaic G2 test

Map of Pilbara coast showing significant sites

Fig 7

The next day, June 21, 1956, the Melbourne Herald reported on its front page that ‘The radio-active cloud from Tuesday’s A-blast on the Monte Bello Islands was last reported 100 miles out to sea off the West Australian coast.’ However ‘An Adelaide report said winds along the north-west coast of Western Australia were blowing from west-south-west at 20,000 ft….Fears about a radio-active fallout grew yesterday when a mining engineer at Marble Bar reported an abnormally high Geiger counter reading after a light rain-shower.’

Nearly thirty years later, on 6 May 1985, the Canberra Times reported  ‘Rain which fell on an inland gold and copper mine after a British atomic bomb test in Western Australia in the 1950s registered high radioactivity, the Royal Commission into British Nuclear Tests in Australia was told at Karratha yesterday. Mr Stewart Stubbs, 78, of Comet Mine, Marble Bar, said he took geiger-counter readings on the ground and on top of his car.

“Both instruments went right off the scale,” he said yesterday. This was about three hours after he had heard a series of explosions which he took to be an atomic blast at the Monte Bello Islands off the north coast. He was driving home to the Comet Mine when he saw thin, flat, dark clouds coming from the coast and pushed by a westerly wind.It started to drizzle and when he reached the mine people asked him if he had heard the atomic bomb. “With the clouds coming over I thought they must be from the Monte Bello blast and could contain fallout,” Mr Stubbs said. “I decided to take some readings on my geiger counter. I had two instruments which I had been using in connection with some uranium exploration work I was doing for the Department of Resources and Energy.” He checked the ground, the top of the car, the clay on his son’s boots and even got a high reading by holding the counter in the air. He radioed Port Hedland airport because he knew Air Force aeroplanes were stationed there and asked to talk to some-one connected with the bomb tests.

The airport put him through to a scientist in a Canberra bomber whose name he now recalled to have been Penney or something similar. (William Penney, now Lord Penney, was the chief scientist for the tests). Mr Stubbs said he told the scientist about the rain, the geiger-counter readings and the cloud. The scientist asked about the make of the counters. Mr Stubbs then asked how dangerous the rain was and the scientist had replied: “I’m afraid I can’t comment.” That same day, Mr Stubbs got people at the mine to wash everything down but it became too dark to finish the job. He also spoke to the matron at the Marble Bar Hospital and told her some people might be sick but not to tell anyone about the fallout because they might become  frightened.’

The full transcript of Mr Stubbs’ testimony to the Royal Commission is available to download at National Archives of Australia NAA:A6488, 14 pp7585ff

The Atomic Weapons Tests Safety Committee Report December 1957

In December 1957,  eighteen months after the second, G2 Operation Mosaic blast at the Monte Bellos, the five scientific members of the Atomic Weapons Safety Committee appointed by the Australian government published a report titled ‘Radioactive Fallout in Australia from Operation ‘Mosaic’ in The Australian Journal of Science.  Relying on data collected  from 6 ‘sampling stations’ on the West Australian coast between Onslow and Broome and including Liveringa, approximately 200 km inland,  this report stated (emphases added)

‘After the second test [June 19, G2] the cloud moved northeast over the Timor Sea without approaching the mainland of Australia. Five hours after firing it was found by aircraft more than 200 miles off the coast covering an area 60 by 40 miles. It continued in a general north-east direction and was again located on this course seven hours later. In order to check that it had not crossed the coast a box search was made of an area of some 70,000 square miles around Darwin on the afternoon of June 20, and another coastal search between Broome and Darwin was made on 21 June. The readings showed that no part of the main cloud had approached closer than 200 miles of the mainland.’ (p 128)


 ‘a pronounced stable layer produced a marked bulge on the stem which trapped a small quantity of particulate material and this was spread to the south-east of the Monte Bello Islands ..The more finely suspended material’ or ‘debris’ was dispersed in the first 48 hours …without scavenging by precipitation except for the very light and isolated shower near Marble Bar.’ (p 129)

The AWTSC 1957 reports a measurement of 128.0 uc/m2 at Port Hedland on June 19 followed by 47.0 at Liveringa and 29.0 at Broome  (Table II – Fallout measurements from explosion G2) p.131. The gummed film measurement devices  at Roebourne ‘only operated for six days commencing on June 19.’ (p131) Table II listed it as ‘Not operating’ after 5 days.

Fig 8 Butement et al, The Australian Journal of Science 20:5:1957 p.130

Royal Commission into British Nuclear Tests in Australia 1984-87

Thirty years after this AWTSC report, in 1985 the Royal Commission into British Nuclear Tests in Australia issued its report (available for download online from the National Archives of Australia) of 18 months of hearings around Australia and in London. In relation to Mosaic G2 it found:

‘7.4.25 The fallout on the mainland following G2 was again [as in G1] greater than expected and occurred at locations where no fallout had been predicted. The post-firing winds behaved similarly to those after Gl, i.e. they weakened and then began to blow to the south and east. An analysis of the trajectories of fallout particles showed that fallout at Port Hedland occurred 24 hours after the explosion and consisted of particles that originated from 20 000 feet in the region of the top of the stem and the bottom of the cloud. Fallout occurred at Derby 24 hours after the explosion of particles that originated at 30 000 feet in the main cloud [RC 270, T24/57). Clearly part of the main cloud did cross the mainland.

7.4.26 The mainland contamination was a result of part of the cloud and stem drifting across the coast.’ 

(emphases added)

Fig 9 Royal Commission Report p 275

The Royal Commission also stated in its Conclusions


(a) The theoretical predictions were incorrect for both Mosaic tests and parts of the clouds passed over the mainland of Australia.

(b) Although the close-in fallout from both Mosaic tests fell into the ocean, fallout also occurred over the mainland and some of it originated from parts of the main cloud. The Safety Committee  communications with the Minister for Supply soon after the second explosion, when it reported that the cloud had not crossed the coast, with the implication that there was no fallout on the mainland, were misleading.’ (emphasis added) The Royal Commission pointed out in 1985 that

‘(c) The level of fallout on the mainland was less than the Level A criterion defined before the Mosaic tests and was also less than the Level AI criterion used at the Buffalo trials for areas in which nomadic Aborigines were living. Although the fallout at Port Hedland satisfied the standards of the time, it did exceed the dose levels applicable later for members of the general public. It was less, however, than the level allowed for occupationally exposed workers.’  (pp 258-9)

The Australian Radiation Protection and Nuclear Safety Agency January 25, 2024

On January 21 2024 John Weiland submitted a query to the Talk  to A Scientist portal of  ARPANSA, the Australian Radiation Protection and Nuclear Safety Agency, asking for information – ‘All I have read seems to acknowledge that Roebourne was in the fall out radius but I find nothing to say if testing was done and if there was any followup on the residents then or now.’ 

The unsigned response four days later told him:

‘Following the Mosaic tests, there was an extensive measurement campaign within the Montebello Islands, and across Australia to monitor any fallout that may have occurred and to assess the level of exposure to Australian service personnel and to the public.  

In your specific case, the most appropriate document I can point you to is the Australian Radiation Laboratory Technical Report 105 from 1992 [which was attached]. This document assessed the potential exposures to the public from fallout due to the nuclear tests. Appendix B & C of this document detail measurements taken for deposited fallout (B) and in air concentrations (C).’

This 32 year old report PUBLIC HEALTH IMPACT OF FALLOUT FROM BRITISH NUCLEAR TESTS IN AUSTRALIA, 1952-57;query=Id:%22library/summary/summary.w3p;query=Author%3A%22Wise,%20Keith%20N.%22 by Wise and Moroney states

‘4.1 Fallout deposit – ‘Fallout deposit samples were collected by exposing a horizontal strip of adhesive film, 30 cm by 15 cm, at a height of 1.2 m above ground’ (p 43)’ – which is to say the size of an A4 sheet of paper. 

The authors acknowledged  that ‘Several sources of error are characteristic of the procedures used’  including ‘statistical uncertainty due to the random nature of radioactive decay’ and ‘errors arising from the small areas of the fallout deposit sample; the inefficiency of the adhesive film for retaining deposited particulates, especially when accompanied by rain.’’ (p 37)

There is  a diagram at p.72 (Figure 6.2(a)) annotated: ‘Trajectories taken by radioactive clouds across Australia for the nuclear tests in the Mosaic and Antler Series. The main debris clouds from Mosaic Rounds 1 and 2 are not shown as they remained largely over the Indian Ocean, moving to the northeast parallel to the coast.’ (emphasis added)

This diagram doesn’t correlate with the maps in the Royal Commission Report north of Broome nor those of the AWTSC report on 1957 south of Port Hedland.

Fig 10 Wise and Moroney 1992 p 72

There is a table somewhat confusingly  labelled CORRECTED FALLOUT DEPOSIT FOR MOSAIC ROUND 2 COLLECTED AT MONTE BELLO IS ON 19 JUNE 1956.

The measurement specifics are not made clear but on June 19, 1956 Broome registered  1444, Liveringa 1741 and Pt Hedland 4741. Roebourne measured ‘less than the minimum detectable on June 19 but 94 on June 20.


The 1992 ARPANSA report that Mr Weiland was sent more than thirty years later in 2024  reports the estimated yield of Mosaic G2 as 60 kilotonnes.  On 26 May 1984  The Canberra Times had reported a New Scientist assertion that ‘a 1956 British nuclear test at Monte Bello, off the northern coast of Western Australia, was three times larger than the Australian Government of the day believed…The New Scientist said the explosion, known as Mosaic G2, was revealed this week in a letter from Britain’s Minister for Defence Procurement, Mr Pattie, to Labour peer, Baron Brockway.

It said the explosion in the Monte Bello Islands group was the “dirtiest” of the 12 tests done by the British in Australia and “atmospheric conditions at the time of the test exacerbated the hazards”. The test was done on Alpha Island in the Monte Bello group on June 19, 1956. ..British Defence Ministry figures showed that Mosaic G2 gave an explosive yield of 60 kilotonnes. The highest yield from a Maralinga test —on October 9, 1957 — was 25 kilotonnes. Others ranged from 1 kilotonne to 15 kilo-tonnes.’

The size of the Mosaic G2 test contrasts with the Australian Government’s official report on the tests. The New Scientist quoted the report as stating, “The explosive yields of the tests in Australia were all in the ‘low’ or ‘kiloton ranges; this means that… in no case was the yield much more than the 20 kilotonnes normally associated with the nuclear weapons used on Japan, and in some cases it was much less”

The report had said that meteorological conditions for each of the two Mosaic tests were such that most of the early fallout went into the sea.”However, in both cases some early fallout crossed the coastline.”                        

On January 1, 1985  the Canberra Times  reported ‘H-bomb tests in Australia denied’:

‘The report, prepared by a consultant nuclear physicist, Mr John Symonds, and tabled in Federal Parliament in June, said Mosaic G2 was a 60-kilotonne test – the largest of all the tests in Australia. Australian and British officials had previously said the test was only 20 kilotonnes. The Symonds report raised questions about whether Mosaic G2 was just a test of a trigger device for a hydrogen bomb or whether it was more closely related to an actual hydrogen bomb test. Mosaic G2 was much bigger than a conventional atomic bomb and generated extensive fallout over Australia. It was more than twice the size of the bomb dropped on Hiroshima.The questions over the tests led the then Minister for Resources and Energy, Senator Walsh, to announce in July the establishment of the Royal Commission headed by Mr Justice James McClelland.’ 

In fact the web site of the Australian Radiation Protection and Nuclear Safety Agency nowadays lists  G2 as 98 kilotons – more than half the yield of the 12 tests done in Australia in the 1950s. 

Fig 10 – scores of files held in the Australian National Archives are ‘Not yet examined’

A UK memo I found in the UK National Archives  that is undated but filed around August 1955  states:

“TESTS IN MONTE BELLO ISLANDS (CODE NAME ‘MOSAIC’) 25 7. We are anxious to carry out two experimental firings consisting of atomic explosions with the inclusion of light elements as boost. The information obtained from these trials should be a vital link in the development of the thermo-nuclear weapon. We wish to carry out these trials next April, before Maralinga will be ready. We had agreed with the Australian Government that we would not test thermo-nuclear weapons in Australia but [emphasis added] Mr. Menzies has nevertheless [emphasis added] agreed to the firings taking place in the Monte Bello Islands (off the North-West coast of Western Australia), which have already been used before for atomic tests. As already explained, the Australians are very sensitive on the question of thermo-nuclear explosions, and although the true character of these tests is understood by the authorities immediately concerned, [emphasis added] knowledge of the trials is restricted to a very small circle and no public statement has so far been made; when it is made, it will therefore require very careful handling.’

The lexicons  of science include maps and diagrams and tables and jargon and argots all of which have mystified what a seven year old schoolboy saw on the school verandah nearly 70 years ago. The authorities persist in telling us  “Children, Best We Forget”.  But in these digital days even we can unpack the texts  and images from our armchairs, although 7 decades after the British atomic and thermonuclear tests started in Australia scores of files held in the Australian National National Archives are marked ‘Not yet examined’. We urgently need to create an independent archive of Australia’s nuclear past.