Operation Buffalo, the first four nuclear tests at South Australia's Maralinga in 1956, includes risky air drop

The nuclear explosion cloud from Breakaway, the fourth Operation Buffalo test at Maralinga in South Australia's northwest in 1956.

Operation Buffalo was the first four, and largest, British nuclear tests in 1956 at Maralinga, part of Woomera prohibited weapons testing area in South Australia, 800km northwest of Adelaide.

The British preferred Nevada, USA, to Maralinga as a test site but that wasn’t feasible with the Americans unwilling to share nuclear technology. The British were trying to catch up with the Americans in developing a hydrogen bomb. Australia banned hydrogen bomb tests on its soil but Maralinga’s tests were linked to the hydrogen bomb (that the British achieved with Operation Grapple in the Pacific in 1957-58).

Operation Buffalo’s first test, One Tree, from a 91-metre tower, used the lighter Red Beard nuclear warhead, boosted with thermonuclear material. Scheduled for September 12, with journalists and politicians to watch, unfavourable weather forced it back to September 27. This costly delay also put pressure on testing Red Beard for British Operation Grapple hydrogen bomb test in the Pacific. 

The One Tree test was at 17:00 in “by no means ideal” weather. The yield was about 16 kilotonnes of TNT and the cloud rose to 11,400 metres – much above predictions. A Canberra bomber flew through the cloud to collect samples. Along with a secondary cloud at 5,000-7,000 metres, it drifted east. Nearest town in its path was Coober Pedy, 317 kilometres away. The main cloud crossed the east coast about 11am on September 28, with the secondary 12 and 18 hours later. Rain on September 29 left some fallout between Brisbane and Lismore in New South Wales.

Next was Marcoo, a ground test using the larger Blue Danube warhead with a low-yield core. The weapon was lowered into a concrete pit. The aircraft bringing Australian politicians was delayed in Canberra and they were rushed to Observation Hill to see the bomb detonated at 16:30, with a yield of 1.5 kilotonnes of TNT. It left a crater 49 metres by 12 metres and fallout crossed the east coast 25 to 30 hours later.

Kite, the third and most difficult test, was  an air drop with a worst-case scenario of radar fuses failing and the bomb detonating on the ground with severe fallout. The RAF practised with high explosive bombs but, after Australian concerns about the dangers of a 40-kilotonne-of-TNT test, a low-yield Blue Danube core with less fissile material was used, reduced to 3 kilotonnes of TNT. On October 11, Valiant B.1 WZ366 became the first RAF aircraft to drop a live atomic bomb. It fell about 91 metres and 55 metres short of the target, detonating at a height of 150 metres. Clouds formed at about 2,100 metres (dropping all its radioactive material inside the prohibited area), and at 3,700 metres, with negligible fallout over South Australia, Victoria and New South Wales.

The Breakaway test was a boosted Red Beard (10 kilotonnes of TNT ) from a 30-metre tower and delayed by weather to October 22. Fallout was measured using sticky paper, air sampling, and water from rainfall and reservoirs. This cloud was tracked with the help of a TAA Douglas DC-4, diverted from its flight path. The cloud reached 11,000 metres but became widely dispersed between Darwin and Newcastle in New South Wales. The highest reading by the ground survey was at Ingomar, South Australia, 310 kilometres from the test.