Due to miscalculation, the most powerful US thermonuclear bomb test, codenamed Castle Bravo, in 1954 created a major ecological and environmental disaster.

A radioactive cloud formed after the Castle Bravo explosion. Photo: US Air Force

On the morning of January 3, 1954, before the sun had risen, the crew of the Japanese ship Daigo Fukuryu Maru, which was fishing off the Marshall Islands in the North Pacific, suddenly saw a bright light in the sky and heard a sound like thunder.

Minutes later, they picked up gray dust on the ship, which many later recalled as “the ashes of death.” By evening, several of them were nauseous and had strange burns on their bodies for no apparent reason. It was not until March 14, when they returned to the mainland, that they learned that they had been exposed to radiation from an infamous American thermonuclear bomb test, according to Slate.fr.

Castle Bravo was the code name for the first dry-fuel thermonuclear bomb test, detonated at Bikini Atoll, Marshall Islands, opening the series of tests of the US's Operation Castle campaign. This was the most powerful thermonuclear bomb detonated by the US with an energy level reaching 15 Megatons (1000 times the energy of one of the two nuclear bombs the US dropped on Japan), far exceeding the initial expected level of 4-6 Megatons.

The explosion created a fireball that could be seen as far away as Kwajalein Island, 450 km away. The force of the blast left a crater 70 m deep and 2,000 m in diameter.

According to Soviet nuclear scientists, the explosion released more energy than expected because American scientists made a mistake in choosing the lithium isotope to make the bomb. This led to a thermonuclear reaction that was so powerful that it could not be controlled.

Before conducting the test, American experts carefully calculated the level of radiation dispersion. Residents living on islands 60 km from the explosion epicenter were evacuated to avoid radiation contamination. Ships moving in the area were also notified not to enter the restricted area.

However, misprediction of weather conditions and sudden changes in wind direction caused the radioactive cloud to be pushed to a higher altitude than expected and to spread beyond the expectations of American experts by nearly 100 km, creating a white dust shower over a very wide area.

According to recorded video footage, the mushroom-shaped radioactive cloud with a diameter of 11 km formed from the explosion reached an altitude of 14 km in just the first minute and then reached an altitude of 40 km with a diameter of 100 km within the next 10 minutes, spreading radiation within a range of 160 km from the epicenter of the explosion, seriously affecting residents living on nearby islands.

Slate.fr experts say the thermonuclear bomb test caused a real environmental disaster. Hundreds of people living on many small islands up to 180 km from the epicenter of the explosion were still exposed to high levels of radiation. Many of them also died one after another from radiation-related illnesses.

In addition, many crew members of ships passing near the bomb testing area were also affected, including the case of radiation exposure of 116 crew members of the US Navy aircraft carrier USS Bairoki, which put these soldiers at high risk of cancer.

The Daigo Fukuryu Maru's communications officer died in the fall of 1954 from acute radiation sickness, and three other crew members died a few years later from various cancers. These sailors were severely exposed to radiation because they had not received an evacuation notice from the US Navy and had inadvertently entered an area 60 km from the epicenter of the explosion.

According to Alex Wellerstein, a history professor from Stevens Institute of Technology (USA), the Castle Bravo thermonuclear bomb test was a warning to the arrogance and ignorance of nuclear scientists at that time when they created a weapon whose power and consequences they did not foresee.

According to VNE