British Atomic Tests in Australia

On May 16, 1956,  the first of a series of two atomic tests, Operation Mosaic, detonated in Australian Territory at the Monte Bello Islands. The British Government and the Royal Air Force exploded two devices code-named Mosaic G1 and Mosaic G2 in the Monte Bello Islands, off the coast near Dampier, Western Australia.

Atomic cloud from Operation Mosaic G1 explosion.
Mosaic G1 cloud as seen from the HMS Narvik. Photo from Nuclear Weapon Archive.

Not the first atomic test on Australian Territory

A ship anchored near the Monte Bello Islandes had previously imploded in Operation Hurricane. This explosion left a crater 6 metres deep and 300 metres wide on the sea floor that can still be located today. To make observation easier, Operation Mosaic would be on land.

The tower used for firing Operation Mosaic G1
The tower used for firing Operation Mosaic G1

Size of explosion not stated.

The British Government stated the second test would be larger than the first but neither would be more than two and a half times that of the bomb previously fired in Operation Hurricane. This meant little, as the yield of Operation Hurricane was not available to Australian officials.

Why Monte Bello and not Maralinga?

At the end of the war, Britain believed it would continue to share nuclear technology with USA, however the USA government ended the cooperation. The nuclear race and Superpower secrecy had begun. A purpose-built site was under construction at Maralinga, but Britain wanted to begin testing as soon as possible. The British Prime Minister assured the Australian Prime Minister that tests would go ahead only if conditions involved no danger to the health of people or animals on the mainland. Further, Australian scientists would be given the same safety checking facilities as Operation Hurricane.

An empty promise?

In fact, Australian scientists had no testing or safety facilities at Hurricane. Following a long and persistent campaign, two Australian officials obtained permission to be present as observers. For Operation Mosaic, three Australian scientists could observe proceedings from a safety point of view.

Public Concern ignored

As the date of the firing drew near (proposed May 14), objections to the tests increased. Perth Protesters claimed Australians were just guinea pigs. The tests went ahead regardless. The May 16 weather forecast was for stability and dryness with winds in an acceptable pattern. The only chance of rain was an isolated shower near Darwin or Cloncurry.

A complete success

Mosaic G1 fired at 1150hrs WA standard time. The mushroom cloud rose to 21,000 feet (6,400 metres) instead of the predicted 14,000 – 17,000 feet. The mushroom ‘ball’ broke away from the stem quickly as a result of low altitude wind shear with the fallout spreading in the predicted north-north-east direction.  The test, considered a complete success, yielded an explosion the equivalent of 15 – 20 kilotons of TNT.

Unpredicted radioactive fallout.

In the following days unexpected locations recorded increased radioactivity. Port Hedland, on the predicted trajectory recorded four times less than Onslow, further south than any predicted path. This was not consistant with recorded wind speed and direction. In the days following a staff member at Royal Adelaide hospital claimed to have taken samples which contained radioactivity. The Radiation Department at Launceston General Hospital measured double the background count-rate for radioactivity between May 26 – 30.

Concern raised in parliament

At the same time, medical experts and atomic scientists released a report on the dangers to humanity from strontium, one of the constituents of radioactive fallout. With increased radioactivity noted as far away as NZ, concerns were raised in parliament. Despite advice from Australian Scientists the Minister stated that the radioactivity was not from the Monte Bello test.

Absolutely no hazard

Despite these concerns the Atomic Weapons Tests Safety Committee report to the Prime Minister on the Monte Bello Atomic Test concluded with the following. ‘From analysis of the detailed data available to us the Safety Committee has satisfaction in reporting that the safety measures were completely adequate. There was absolutely no hazard to persons or damage to livestock and other property’.

Book cover. Atomic Thunder
Excellent reading Atomic Thunder


A History of British Atomic Tests in Australia, produced by the Australian Government in 1985 and The Report of the Royal Commission Into British Nuclear Tests in Australia – a 420 page downloadable file.


Atomic Thunder