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On Monday March 1st, 1954, at 6:45 in the morning, the US carried out its largest nuclear detonation ever – CASTLE BRAVO – at the Bikini Atoll in the south Pacific Marshall Islands. Both military servicemen and Marshall Islanders got to experience first-hand what Armageddon would truly be like. The explosion turned out to be 2.5 times bigger than planned and caused far higher levels of radioactive fallout than ever predicted. Castle Bravo was the worst radiological disaster in American atomic history.
The Manhattan Project, lead by Robert Oppenheimer, developed the first atomic bombs used on Hiroshima and Nagasaki Japan. Not long after, the Soviet Union developed the bomb as well, leading to the nuclear arms race and The Cold War. This lead to the issue, for both sides, of where to test such deadly weapons and deal with the resulting radioactive fall out.
The Marshal Islands’ isolation had proved a blessing throughout their history. The small island chain, about 1,800 miles from Papua New Guinea, was free from outside conflict until World War II, when it served as a Japanese outpost. After the war, the US took over the atolls, which is when their remoteness became their curse.
The U.S. military realized its isolation made it ideal for testing nuclear bombs. In 1946, the US military governor asked the native Bikini Atoll residents to temporarily relocate for “the good of mankind.” The islanders agreed believing they would be able to return to their homes after a few months. Bikini Atoll would remain uninhabitable for more than 70 years.
The Bravo bomb was the first in Operation Castle, a series of thermonuclear tests by the US military.
Nicknamed Shrimp, the bomb weighed 23,500 pounds and was America’s first weaponized hydrogen bomb meant to be delivered by bomber. “Shrimp” ended up yielding the equivalent of 15 megatons of TNT. Scientists had seriously miscalculated and expected only FIVE. They based the location of observation posts and ships outside a “Safety Exclusion Zone” on a 5 megaton yield.
Zero hour for Castle Bravo was at just after dawn at 6:45 am local time. Officers, scientists, and serviceman yawned and drank black coffee as they stretched and waited. From the moment the bomb detonated, everyone knew something had gone terribly wrong. A so-called ‘tritium bonus’ occurred in the nuclear reaction, causing extremely energetic fusion. An explosion began that can only be described as Apocalyptic.
The flash was overwhelming, even by the standards of atomic bombs. Men saw their bones appear as shadows through their skin. Blinding light burst through the smallest cracks in secured doors. Bravo’s blast wave was far more intense than expected. 30 miles away from Ground Zero, Navy sailors said the heat was “like having a blowtorch applied to their uniforms.” Battle-hardened World War II veterans took to their knees to pray, believing the atmosphere had caught fire and they were witnessing the end of the world.
Seconds after detonation, a mushroom cloud 4.5 miles wide began to rapidy grow. It rose 1,000 feet per second into the sky, topping out at 130,000 feet. The shock wave destroyed buildings outside of the expected damage zone, and nearly knocked observation planes out of the sky, miles away. The fireball itself was hotter than the surface of the sun!
Castle Bravo ended up being 1,000 times more powerful than Hiroshima and Nagasaki.
The explosion left a 250 feet deep crater on the ocean floor, a diameter of 6,500 feet. But that was just the beginning of the disaster. It released so much radioactive debris into the atmosphere that it fell over 7,000 square miles. It contaminated the inhabitants of ALL the nearby Marshall atolls, the US servicemen present, and even the unfortunate crew of a Japanese fishing trawler, miles away.
To make matters worse, weather forecasters predicted that high-altitude winds would blow the fallout away from inhabited islands. Instead, the wind blew the radioactive cloud toward them. Fallout rained down on ships and sailors. Captains ordered entire crews below decks, and sealed all hatches for days to escape contamination. Despite knowing the risk of spreading fallout to nearby inhabited islands, Major General Percy Clarkson had ordered the test to continue as planned.
The wind spread radioactive particles downwind, affecting the inhabited atolls of Rongelap, Utirik, and Ailinginae. Fallout dusted U.S. servicemen stationed on nearby Rongerik Island. Approximately 5 hours after the detonation, it began to rain radioactive fallout at Rongelap. Within hours, the atoll was covered with a fine, white powder. None of the inhabitants knew it was radioactive fallout.
Delighted children giggled and played in the ‘snow,’ even licking it off their hands
About 90 minutes after the explosion, the fallout reached an unfortunate Japanese fishing boat, the Daigo Fukuryū Maru (Fifth Lucky Dragon), 80 miles east of the test site. All 23 crew members were severely exposed to high levels of radiation, one dying months later. Their irradiated fish were brought back to Japan and unknowingly entered the market, later causing a panic. With the memory of Hiroshima only 9 years earlier, this created a diplomatic nightmare and provoked international outrage. The U.S. eventually agreed to pay more than $15 million in compensation to the Fukuryu Maru survivors.
Emergency evacuations by the US were too slow to limit lethal doses of radiation and islanders didn’t know about the consequences of fallout. The U.S. military evacuated Rongelap 2 days after the test, relocating them to Majuro, the capital. Within a week, the U.S. launched a study on the effects of radiation on the islanders and provided medical care. The military however never explained to the inhabitants that a study was being conducted on them. Rarely was a translator even present. Marshallese were given potassium iodide pills with no explanation as to why. For years later, Marshall islanders experienced numerous health problems, including birth defects and thyroid cancer.
Since Castle Bravo, the U.S. has had to provide more than $1 billion to the affected atolls which includes medical treatment, health care, island rehabilitation and resettlement. The two countries reached a bilateral agreement designed to award compensation to victims of cancers and other serious health effects, such as burns and birth defects.
Atmospheric wind shear and ocean currents continued to spread fallout from the explosion.
Traces of radioactive material were later found in Japan, Australia and even India. Castle Bravo was not the first test at Bikini Atoll, the US held 67 atmospheric tests in the Pacific Ocean through 1958. And the US was not the only country conducting atmospheric testing in its territories. The Soviet Union equaled the US in its Cold War nuclear testing program.
Marshall Islanders finally began to return home in the early 1970s, nearly 30 years after testing began. However, surveillance in 1978 found that the inhabitants of Bikini Atoll exhibited dangerously high levels of radioactivity and the entire population was once again evacuated. The island natives are still in forced exile. Today, the danger comes from consuming contaminated food or water. The detonation crater is still visible from the air and looks like a fierce dragon took a chomp out of the atoll. In a way, it had.
Castle Bravo triggered a backlash around the world against atmospheric nuclear testing. In 1955, the United Nations created the Scientific Committee on the Effects of Atomic Radiation. In 1963, the Limited Test Ban Treaty between the U.S. and the Soviet Union, finally prohibited nuclear testing in the atmosphere or underwater. For better or worse, nuclear tests could henceforth only be conducted underground.
Castle Bravo’s fallout even inspired the creation of a Japanese science fiction movie legend, the great reptile Godzilla, “King of Monsters.” Using nuclear power to instead generate electricity became a whole different issue and led to later disasters like Three Mile Island in the US, Chernobyl in Ukraine and Fukushima in Japan.