Less than one year after the United States tested its first hydrogen bomb, the Soviets detonate a 400-kiloton device in Kazakhstan. The explosive power was 30 times that of the U.S. atomic bomb dropped on Hiroshima, and the mushroom cloud produced by it stretched five miles into the sky. Known as the "Layer Cake," the bomb was fueled by layers of uranium and lithium deuteride, a hydrogen isotope. The Soviet bomb was smaller and more portable than the American hydrogen bomb, so its development once again upped the ante in the dangerous nuclear arms race between the Cold War superpowers.
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