__1961: __The Soviet Union detonates the largest nuclear or thermonuclear weapon ever constructed.

The Tsar Bomba (as it was known in the West; the Soviets referred to it as Big Ivan or, more officially, RDS-220) was a three-stage hydrogen device with a 100-megaton capacity. Andrei Sakharov, who later suffered a crisis of conscience and became a celebrated Soviet anti-nuclear dissident, was the project leader and senior weapons designer.

Soviet Premier Nikita Khrushchev ordered the building of the bomb during a meeting with Sakharov in July 1961. To say it was completed quickly is to say the least: The elapsed time from conception to detonation was a mere 16 weeks.

The bomb weighed 27 tons and was so big that the largest Soviet bomber, a Tu-95 "Bear," had to be heavily modified to accommodate both its girth and its weight.

The Tsar Bomba was built for midair detonation. An elaborate, five-stage parachute system was designed, with a main canopy area of 5,400 square feet to slow the bomb's descent, so the plane had time to clear the area.

That was accomplished with relative ease, but other design problems arose as the bomb neared completion. This might have caused a delay in testing if Sakharov hadn't overruled the skeptics while ramming through a few late modifications.

The bomb was dropped at around 11:30 a.m. Moscow time from an altitude of 6 miles above the Mityushikha Bay test range on the Arctic Sea island of Novaya Zemlya. It detonated in three stages at an altitude of 2.5 miles.

The explosion resulted in a cloud that boiled 210,000 feet (40 miles) into the sky. Its force obliterated every building in the deserted village of Severny, 34 miles from ground zero, and damaged structures more than 600 miles away.

Had the Tsar Bomba been detonated with its full 100-megaton force, the resulting fallout would have totaled 25 percent of all fallout emitted since Hiroshima. Although the actual yield has been disputed over the years, the number usually assigned is 50 megatons of TNT (more than 3,300 Hiroshima-size bombs).

Even at half its capacity, the bomb resulted in by far the largest man-made explosion ever. Its flash was visible from 600 miles away. According to one witness who visited ground zero in the aftermath: "The ground surface of the island has been leveled, swept and licked so that it looks like a skating rink. The same goes for rocks. The snow has melted and their sides and edges are shiny. There is not a trace of unevenness in the ground.... Everything in this area has been swept clean, scoured, melted and blown away."

For his role in the test, bomber pilot and mission commander Maj. Andrei E. Durnovtsev was promoted to lieutenant colonel and made a Hero of the Soviet Union.

The bomb came along at a time of tense relations between the United States and the USSR. Nearly two years had passed since Khrushchev's speech declaring the Soviet Union's support for wars of national liberation, only six months since the U.S. fiasco at the Bay of Pigs, and barely two months since the construction of the Berlin Wall. The two countries were actually involved in nuclear-test-ban negotiations, and the timing of the test was seen largely as a measure of Khrushchev's dissatisfaction with the way things were going.

In reality, the Tsar Bomba was impractical, more effective as a propaganda weapon than anything else. The bomb was too large to be delivered by an ICBM, meaning it could only be delivered by strategic bomber. The only three American metropolitan areas sprawling enough to warrant being targeted by such a weapon (New York, Chicago and Los Angeles) required at least eight hours of flying time over enemy airspace and were therefore unreachable, owing to U.S. air defenses.

Still, the bomb was an excellent example of the Russian penchant for gigantism. Even the western nickname itself, Tsar Bomba, or "King of the Bombs," was inspired by other Russian behemoths: Tsar Kolokol, the world's largest bell, and Tsar Pushka, the world's largest cannon, both on display at the Kremlin.

Two Tsar Bombas were built. The one they didn't drop, a dummy, remains on display at the Russian Atomic Museum in Arzamas-16 (now Sarov), the formerly secret city where the bomb was built.

Source: Various