The link between Castle Bravo and modern environmentalism

By William Souder, March 3, 2014

Sixty years ago, in the predawn hours of March 1, 1954, a Japanese tuna boat named Daigo Fukuryu Maru (“Lucky Dragon no. 5”) was fishing near the Marshall Islands in the central Pacific. Its engine off, the ship drifted silently on a glassy sea. Overhead, the stars illuminated a few wandering clouds. Suddenly a blinding wall of light appeared on the western horizon. As the crew rushed on deck, the light changed from white to yellow, and then to orange and finally a deep red—a monster light that continued to grow and rise into the sky. After a few minutes, the 99-ton ship lurched as a deafening roar passed over it.

Racing to the chart room, the ship’s radio operator—a man named Aikichi Kuboyama—made a hasty calculation. Estimating that the sound wave had reached the ship about seven minutes after they first saw the light, Kuboyama figured they were roughly 87 miles away from whatever had happened. Looking at his chart, Kuboyama saw that there was nothing in that direction but open water and a few small piles of sand called Bikini Atoll, 85 miles to the west.

Terrified, the crew began the long process of hauling in their line. After a few hours it began to snow—or, rather, something like snow started to fall from the sky. When the men looked at it closely—a few tasted it—the stuff seemed more like ash or sand. It was sticky and irritated the men’s hands as they worked to get under way. Down it came, coating the ship and the men, getting into their hair and clothing, and in due course finding its way inside, into the crew’s quarters, the galley, everywhere. As the “Lucky Dragon” headed for home, the crew fell sick with nausea. A yellowish discharge oozed from their eyes, and their skin steadily darkened until it was nearly black. By then they were convinced they had somehow gotten too close to a test of an atomic bomb. They hadn’t been lucky after all.

The test at Bikini Atoll that day—code named Castle Bravo—was of the first practical hydrogen bomb. A year and a half earlier, the United States had exploded the first hydrogen device, which was the size of a small building. The device in the Castle Bravo test, dubbed “Shrimp,” was small enough to be carried on a bomber. It was packing a big surprise. Moments after touching the trigger on the other side of a lagoon 30 miles away, the men conducting the test felt the command bunker moving backward before they even heard the explosion. They realized they were feeling the ground shock, which travels through the earth faster than the speed of sound.

It turned out that, owing to a miscalculation of how lithium isotopes in the explosive fuel would react, Shrimp had produced a blast two and a half times more powerful than expected—some 15 megatons, or the equivalent of 1,000 Little Boys, the bomb that had destroyed Hiroshima. Hot gas and debris from the blast—highly irradiated sand and pulverized coral—shot through the troposphere to a height of about 115,000 feet.

And then it started coming back down, some of it atop the ship.

The crew would spend months being treated for radiation sickness in a Tokyo hospital. All but the radio operator Kuboyama eventually recovered, although many later suffered from liver and blood disorders.

The Castle Bravo incident caused international consternation. The United States and the Soviet Union were already locked in a fierce nuclear arms race that would continue through the 1950s and into the 1960s. And as these much more powerful fusion devices began to be routinely tested above ground, the Earth’s atmosphere would become steadily more contaminated with bomb debris. This fell back to earth—much more quickly than many scientists expected—as radioactive fallout, which would come to be seen as the greatest danger in a nuclear war.

A few years later, marine biologist and author Rachel Carson recounted Kuboyama’s death in the most sensational book of 1962: Silent Spring. A stern polemic on the dangerous overuse of synthetic pesticides such as DDT, Carson’s book explained how these chemical poisons were a threat to wildlife and to human health. Silent Spring alarmed the public and made Carson the target of an angry, well-financed smear campaign by the chemical industry.

One of Carson’s challenges in writing Silent Spring was how to convince her readers of the then-novel idea that an unseen chemical contaminant that might be anywhere (or everywhere) might cause unanticipated collateral damage to ecosystems. She solved this problem by perceiving a parallel between pesticides and radiation. Invisible, ubiquitous, and accumulating in the tissues of living things over time, pesticides and radioactive fallout from nuclear testing were, Carson argued, the twin existential problems of the modern age.

In June 1962, as Silent Spring was being serialized in The New Yorker magazine, the United States alone tested 17 nuclear devices. That year, a nuclear explosion occurred somewhere in the world every few days. Fearful of the steady rain of fallout—which had begun turning up in cow’s milk in the American Midwest—the public was receptive to the idea that pesticides belonged in the same category as radiation. In Silent Spring, Carson told the story of a farmer who had died after spending a day dusting his land with DDT, and how it was reminiscent of the story of the radio operator Kuboyama. “Like Kuboyama, the farmer had been a healthy man gleaning his living from the land as Kuboyama had taken his from the sea,” Carson wrote. “For each man a poison drifting out of the sky carried a death sentence.”

Silent Spring, long since acknowledged as one of the most important books of the 20th century, was published in September 1962. A month later the island of Cuba was under a US naval blockade, and America and the Soviet Union were on the brink of war. When Rachel Carson announced to the public that pesticides had become “the sinister and little-recognized partners of radiation in changing the very nature of the world,” everyone got the message.

Editor's note: An editorial that deals with Castle Bravo and other early hydrogen bomb tests can be found in the May 1954 issue of the Bulletin of the Atomic Scientists.

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