March 1 - Bikini's weather outlook downgraded to "unfavorable" and Joint Task Force 7 directs several ships to move 20 miles to the south to remove them from the expected fallout zone. Despite weather reports showing that winds are blowing in the direction of inhabited islands, the March 1 Bravo hydrogen bomb test is detonated at Bikini. At 15 megatons, it is 1,000 times the strength of the Hiroshima bomb.

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.
 

Within hours a gritty, white ash is enveloping islanders on Rongelap and Ailinginae Atolls. A few hours later, American weathermen are exposed to the snowstorm of fallout on Rongerik, and still later the people of Utrik and other islands experience the fallout "mist". Those exposed experience nausea, vomiting and itching skin and eyes. March 3 Rongelap islanders are evacuated 48 hours later, and Utrik is evacuated 72 hours after Bravo. Both groups are taken to Kwajalein for observation. Skin burns on the heavily exposed people begin to develop, and later their hair falls out. The U.S. Atomic Energy Commission issues a statement to the press calling Bravo a "routine atomic test", and stating that some Americans and Marshallese were "unexpectedly exposed to some radioactivity. There were no burns. All were reported well."

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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.

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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.

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The Rongelapese, not understanding what was happening, watched as two suns rose that morning, observed with amazement as the radioactive dust soon formed a layer on their island two inches deep turning the drinking water a brackish yellow. Children played in the fallout; their mothers watched in horror as night came and they began to show the physical signs of exposure. The people experienced severe vomiting and diarrhea, their hair began to fall out, the island fell into a state of terrified panic. The people had received no explanations or warnings whatsoever from the United States government. Two days after the test the people of Rongelap were finally taken to Kwajalein for medical treatment.