Early in the morning on March 1, 1954, the hydrogen bomb, code named Bravo,
was detonated on the surface of the reef in the northwestern corner of Bikini
Atoll. The area was illuminated by a huge and expanding flash of blinding
light. A raging fireball of intense heat that measured into the millions of
degrees shot skyward at a rate of 300 miles an hour. Within minutes the
monstrous cloud, filled with nuclear debris, shot up more than 20 miles and
generated winds hundreds of miles per hour. These fiery gusts blasted the
surrounding islands and stripped the branches and coconuts from the trees.
Joint Task Force ships, which were stationed about 40 miles east and south of Bikini in positions enabling them to monitor the test, detected the eastward movement of the radioactive cloud from the 15 megaton blast. They recorded a steady increase in radiation levels that became so high that all men were ordered below decks and all hatches and watertight doors were sealed.
Millions of tons of sand, coral, plant and sea life from Bikini's reef, from three islands [Bokonijien, Aerokojlol, Nam] and the surrounding lagoon waters were sent high into the air by the blast. One-and-a-half hours after the explosion, 23 fishermen aboard the Japanese fishing vessel, the Lucky Dragon, watched in awe as a "gritty white ash" began to fall on them. The men aboard the ship were oblivious to the fact that the ash was the fallout from a hydrogen bomb test. Shortly after being exposed to the fallout their skin began to itch and they experienced nausea and vomiting. One man died.
Meanwhile, on Rongelap Atoll (located about 125 miles east of Bikini), three to four hours after the blast, the same white, snow-like ash began to fall from the sky onto the 64 people living there and also onto the 18 people residing on Ailinginae Atoll. Bravo was a thousand times more powerful than the Fat Man and Little Boy atomic bombs that were dropped on Nagasaki and Hiroshima during the end of World War II. Its "success" was beyond the wildest dreams of the American scientists who were involved in the detonation--they thought that the blast would only carry a payload of approximately 3 megatons.
Castle Bravo was a lithium-deuteride fuelled H-bomb exploded 1st March 1954 at Bikini Atoll. It yielded 15 megatons and had a fireball 4 miles in diameter. It was much bigger than the test crews had been expecting. It engulfed its 7,500 foot diagnostic pipe array all the way out to the earth-banked instrument bunker, which barely survived. Test crews were trapped in experiment bunkers well outside the expected limits of its effects. It menaced task force ships, one of which held Marshall Rosenbluth, a U.S. theoretical physicist, "I was on a ship that was thirty miles away, and we had this horrible white stuff raining down on us. I got 10 rads [100 chest x-rays] of radiation from it. It was pretty frightening. There was a huge fireball with these turbulent rolls going in and out. The thing was glowing. It looked to me like a diseased brain up in the sky. It spread until the edge of it looked as if it was almost directly overhead. It was a much more awesome sight than a puny little atomic bomb. It was a pretty sobering and shattering experience." Bravo vaporized a crater 250' deep and 6,500' in diameter out of the atoll rock. The 'horrible white stuff' was calcium precipitated from vaporized coral.