Ivy Mike, 1 November 1952 - first full-scale thermonuclear test

The Ivy Mike device weighed 82 tons

The island of Elugelab before the test

The island of Elugelab after the test

1 November 1952 - Ivy Mike

The Ivy Mike device measured 6 x 2 metres.

It was on the eve of Halloween 1952 in the United States when 9,000 kilometres away, American scientists tested the first hydrogen bomb on the Marshall Islands. With an explosive yield of 10.4 megatons, the Ivy Mike (M for megaton) test had around 700 times the explosive power of the weapon dropped on Hiroshima seven years earlier, killing 160,000 people. Ivy Mike set the infamous record of the largest explosion until then and would be the fourth largest U.S. nuclear test ever conducted.

The island of Elugelab is missing.Gordon Dean, chairman of the Atomic Energy Commission summarizing the events to President Eisenhower
Something I will never forget was the heat. Not the blast...the heat just kept coming, just kept coming on and on. Its really quite a terrifying experience because the heat doesn't go off....on kiloton shots its a flash and its over, but on those big shots its really terrifying.Harold Agnew, Observing from a ship 40 km away
Ivy Mike introduced the two-staged design typical for modern thermonuclear weapons.

The Ivy Mike test was built on the principles of a thermonuclear device first tested one year earlier during the George test. It used a Nagasaki-type implosion device to trigger a secondary bomb - a 30 centimetre thick tank in the shape of a cylinder filled with cooled liquid deuterium, a stable isotope of hydrogen. While the trigger used the principle of nuclear fission, the secondary drew its energy from fusion, the same reaction that powers the sun.

Ivy Mike measured six metres in height and two metres in diameter. Due to its shape, the scientists also called it “sausage”. Weighing 82 tons, the device was not a deliverable weapon and required a hangar sized building to house it. Soviet engineers allegedly (and derisively) referred to it as a "thermonuclear installation".

As the cloud cooled, it began to billow outward. Its colors lost their infernal intensity, paled to harmless-looking but deadly pastels. Then, slowly the 100-mile-wide cauliflower drifted away and disappeared.TIME Magazine, issue 26 April 1954

The detonation produced a cloud that boiled up to 50 kilometres into the stratosphere, reaching a width of over 100 kilometres. At a distance of 50 kilometres, scientists observed the explosion from a boat. They had underestimated the yield and could see the cloud right over their heads and feel the irradiated coral debris raining down on them. The Elugelab (“Flora”) Island, where Ivy Mike was installed, was entirely vaporized, leaving only a 50 metre deep crater. The radioactive fallout was blown over the Pacific and the neighbouring Marshall Islands; see chapter effects of U.S. nuclear testing.

Jawaharlal Nethu (left), with Mahatma Gandhi

Unlike with other tests, all information about the Ivy Mike test was initially kept secret in order to prevent the Soviet side from gaining any information, in particular about radioactive measurements. In 1954, two years after Ivy Mike, some of the original footage was released to the public. It was quickly picked up by media in the United States and in other countries, fuelling protests against nuclear testing. The Soviet Union warned that devices like Ivy Mike could destroy “the fruits of a thousand years of human toil”. That same year, Prime Minister of India Jawaharlal Nehru called for a “standstill agreement” on nuclear tests.

The TX-16 JUGHEAD was deployed as the direct descendant of the Ivy Mike device.

Yet Ivy Mike was followed by many other hydrogen bomb tests. Five deployable bombs built on its structure were produced in January 1954. These weaponized versions were scheduled to be tested during the Operation Castle, a test series of hydrogen based bombs in March of the same year, but they were not detonated due to the “success” of the Castle Bravo test. Yielding 15 megatons, this was the largest U.S. nuclear test and is considered the worst radiological incident in U.S. nuclear testing history, with fallout contaminating populated islands and a Japanese fishing trawler.


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Next featured nuclear test:

8 November - Grapple X, UK's first thermonuclear test