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In an attempt to end the war in the Pacific without a costly invasion of Japan, the US dropped two atomic bombs on the Japanese cities of Hiroshima and Nagasaki on August 6 and 9, 1945 respectively. A uranium gun-type atomic bomb named Little Boy was dropped on Hiroshima. When Emperor Hirohito did not heed President Truman’s call for surrender, the US dropped a plutonium implosion-type bomb named Fat Man on Nagasaki.

The two atomic bombings, together with the Soviet Union’s declaration of war on Japan, finally convinced Emperor Hirohito to surrender to the Allies, effectively ending World War II. Use of the atomic weapons demonstrated America’s technological superiority, but also increased existing tensions with the Soviet Union, setting the stage for the Cold War.

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On November 1, 1952 at 7:15am local time (October 31, 1915 hours GMT), the United States tested its first thermonuclear device (hydrogen bomb) on the island of Elugelab in the Eniwetok Atoll in the Marshall Islands about 3,000 miles west of Hawaii. Code named Ivy Mike, the device was detonated remotely from a distance of about 30 miles.

The resulting fireball was 3 miles wide and reached a height of 120,000 feet. The mushroom cloud that followed the fireball was 100 miles wide. The yield of the explosion was a little over 10 megatons, more than 700 times larger than the atomic bomb dropped on Hiroshima. Elugelab was vaporized and the crater left behind was more than a mile wide and more than 160 feet deep.

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Known as Big Ivan to the Soviets and as Tsar Bomba in the US, RDS-220 was the largest nuclear weapon ever built. Designed as a 100 megaton hydrogen bomb, its yield was reduced by 50% when it was tested. The device was air-dropped from an altitude just above 34,000 feet over the Mityushikha Bay test site on Novaya Zemlya Island on October 30, 1961.

It detonated at 13,000 feet and its fireball still reached the earth. The blast pressure was measured at 300 psi and the flash of light was visible more than 600 miles away. The mushroom cloud reached an altitude of 210,000 feet.

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In early November of 1983 the world may have come closer to nuclear war than at any time since the Cuban Missile Crisis. NATO was conducting what it considered a routine exercise named Able Archer, a simulation designed to train and test the procedures for shifting from conventional to nuclear war.

However, the Soviet Union interpreted the exercise as a prelude to a first strike by the United States. Much remains classified about what came to be known as the War Scare of 1983. But the National Security Archive has amassed and published a large collection of documents that are available online. Included in this library is a 100-page report by the President’s Foreign Intelligence Advisory Board from February of 1990 entitled The Soviet “War Scare.” Declassified in 2012, the moderately redacted report concludes that the intelligence community did not “attach sufficient weight to the possibility that the war scare was real”, and as a result “the President was given assessments of Soviet attitudes and actions that understated the risks to the United States.” The Board further concluded that the US had “inadvertently placed our relations with the Soviet Union on a hair trigger.”