The H-bomb test that went nuclear

The decision facing President Truman in January 1950 over whether to build a hydrogen bomb was, the Washington Post said, potentially the gravest and most difficult “that has confronted any chief of the State in war or peace in American history. It may determine the survival of the civilisation that the western world has known for 2,500 years”.

On January 31, the President announced that he had ordered the Atomic Energy Commission to press ahead. The race to stockpile conventional nuclear weapons would continue, but the priority was to develop workable – and portable - weapons using thermonuclear (fusion) explosions, in which compressed hydrogen was exploded by a primary fission bomb, which then set off a third fission stage of the bomb’s outer casing. Hydrogen was a cheap and accessible fuel, and the explosive potential of the fission-fusion-fission chain reaction was vastly greater than that of the atom bomb.

Over the next two years, H-bomb tests were conducted in Nevada before concern about radioactive fallout moved proceedings to the Marshall Islands of the Pacific. The first test explosion there made a crater in the ocean floor a mile wide and 175ft deep.

Russia’s H-bomb programme was not far behind. After its first test, in 1953, Pravda gloated: “As the result of the possession of the mighty power of thermonuclear fission … the explosion was of great strength. The power of the hydrogen bomb is many times greater than the power of atomic bombs.”

Consternation about the escalating scale of the nuclear arms race was world-wide. In the UK, Church leaders called for an international inspection and control body. The Times reported on a pilot exercise to assess the effect of a nuclear explosion over London, ground zero being 200 yards to the south east of Clapham Junction.

The conclusion, that “allowing for the evacuation of priority classes beforehand … and with warning of the attack, about 16,000 would be killed or trapped and 3,000 injured”, looked foolish before it was even published. In a similar study in New York, a US civil defence official said, with masterly understatement, “the ‘duck-when-you-hear-a-bang’ concept of civil defence is a thing of the past”.

The escalation culminated at Bikini Atoll on March 1, 1954, with the 15 megaton Castle Bravo, 1,200 times larger than the A-bombs that destroyed Hiroshima and Nagasaki, and the biggest atmospheric explosion ever carried out by the United States.

The worried world was not reassured to learn that the size of the explosion had been accidental. The Times reported President Eisenhower saying that “something must have happened at the test which surprised and astonished scientists”.

The Atomic Energy Commission denied that the explosion had been “out of control”, as had been suggested. “Its yield had been about double that of the calculated estimate – a margin of error ‘not incompatible with a totally new weapon’”.

The megatonnage, caused by a miscalculation at Los Alamos, was not the only “error”. A change in wind direction meant that radioactive fallout affected inhabited islands, whose residents were hastily evacuated, and a Japanese fishing boat 70 miles from the blast was blanketed with ash.

The fate of the 23 fishermen on the Fukurya Maru, or Lucky Dragon, did more than anything else to sound the alarm on nuclear proliferation. Interviewed by Life magazine, they described seeing the sky turn red, then iron grey, and hearing the explosion six minutes later, “like many thunders rolled into one”.

Then came the fallout. Captain Tsutsui said that ash “fell into my eye and began to burn”. The crew were too sick to eat and their skin started to itch. Some hours later, “our faces felt very hot, and then … began to turn this pencil-lead colour.”

The fishermen were sick for months; in September, one, Aikichi Kuboyama, died, his family receiving £1,000 in compensation. There was panic in Japan over contaminated fish stocks, and despite efforts to play down the longevity of radioactive damage, the world woke up to the knowledge that science had unleashed something that could not be undone.

Headed, "A hideous reality", a Times leader on March 26 asked, “if one side has bombs capable of blowing up half the world, is it necessary as a deterrent for the other side to have bombs capable of blowing up three-quarters of it?” It urged further efforts at an international détente:

“Mankind, if it is to survive, can never give up trying. Some day the decisive date for good or ill will arrive. It is at least worth seeing whether that date was not March 1.”

The public had already decided. This letter, published in The Times, summed up the feelings of a generation:

Sir, In the bus, on the way to school, I asked one of our small boys (aged 11) what he intended to be when he grew up. He replied, “Sir, I need not worry, as by that time there will be nowhere to grow up on.” Yours faithfully, etc.