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On March 1, 1954 the United States detonated a hydrogen bomb on the Pacific island of Bikini. It was the most powerful nuclear device ever detonated by the United States, with a yield of 15 megatons which far exceeded the expected 4 to 6 megatons. This bomb was about 1,000 times more powerful than the atomic bomb that destroyed Hiroshima in World War II. The bomb formed a fireball almost four and a half miles across within a second. This fireball was visible on the Kwajalein atoll over 250 miles away. The mushroom cloud reached a height of 47,000 feet and a diameter of 7 miles in about a minute and eventually spread about 100 miles across. The cloud contaminated more than seven thousand miles of the surrounding Pacific Ocean and seriously affected the crew of a Japanese fishing boat that was within 80 miles of the test zone. Two hundred sixty-four people were exposed to large doses of radiation because the explosion and fall-out were much greater than expected. Hopalong Cassidy was the title character in a hugely popular television series of the time. Hopalong could always be counted on to come to the rescue, but even he could not help with the H-bomb.

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