U.S. President Harry S. Truman publicly announces his decision to support the development of the hydrogen bomb, a weapon theorized to be hundreds of times more powerful than the atomic bombs dropped on Japan during World War II.

Five months earlier, the United States had lost its nuclear supremacy when the Soviet Union successfully detonated an atomic bomb at their test site in Kazakhstan. Then, several weeks after that, British and U.S. intelligence came to the staggering conclusion that German-born Klaus Fuchs, a top-ranking scientist in the U.S. nuclear program, was a spy for the Soviet Union. These two events, and the fact that the Soviets now knew everything that the Americans did about how to build a hydrogen bomb, led Truman to approve massive funding for the superpower race to complete the world’s first “superbomb,” as he described it in his public announcement on January 31.

On November 1, 1952, the United States successfully detonated “Mike,” the world’s first hydrogen bomb, on the Eniwetok Atoll in the Pacific Marshall Islands. The 10.4-megaton thermonuclear device, built upon the Teller-Ulam principles of staged radiation implosion, instantly vaporized an entire island and left behind a crater more than a mile wide. The incredible explosive force of Mike was also apparent from the sheer magnitude of its mushroom cloud–within 90 seconds the mushroom cloud climbed to 57,000 feet and entered the stratosphere. One minute later, it reached 108,000 feet, eventually stabilizing at a ceiling of 120,000 feet. Half an hour after the test, the mushroom stretched 60 miles across, with the base of the head joining the stem at 45,000 feet.

Three years later, on November 22, 1955, the Soviet Union detonated its first hydrogen bomb on the same principle of radiation implosion. Both superpowers were now in possession of the “hell bomb,” as it was known by many Americans, and the world lived under the threat of thermonuclear war for the first time in history.

READ MORE: Atomic Bomb History