Moscow built a 100-megaton bomb called the TSAR BOMBA (“King of Bombs” officially the RDS-220), tested the day before Halloween, on October 30, 1961. TSAR was deliberately tested to only half strength, 50-60 megatons, by removing the third stage. No bomber could survive if TSAR were tested to full strength. At 100 megatons, TSAR would have covered much of Russia with radioactive fallout, though tested in far Novaya Zemlya beyond the Arctic Circle.
TSAR was a three-stage thermonuclear weapon. The first stage used fission to compress a thermonuclear second stage, just like in a normal H-bomb, except the first and second stages were more powerful, yielding 50-60 megatons, already twice as powerful as the biggest U.S. H-bomb ever built.
TSAR’s thermonuclear second stage was designed to compress another thermonuclear third stage and to fission a uranium tamper. All three stages would release an estimated 100-150 megatons. The third stage would also, by fissioning uranium, produce enormous amounts of radioactive fallout.
As noted above, TSAR’s third stage was not tested to reduce blast and fallout.
TSAR is the most powerful nuclear weapon ever built, even at half strength yielding the biggest explosion ever produced by mankind — releasing more than 10 times the energy of all the ordnance exploded in World War II. 100 megatons is energetically equivalent to 10,000 Hiroshima A-bombs or 1,000 U.S. W80 H-bombs (yield 100 kilotons). The most powerful bomb ever deployed by the U.S. is the B41 (yield 25 megatons) scrapped in 1976.
When testing the TSAR — even though tested only to half strength — the Soviets estimated their bomber crew only had a 50 percent chance of surviving its blast and thermal effects. Its enormous fireball was visible at a distance of 1,000 kilometers (620 miles). TSAR’s shockwave was observed rippling the atmosphere at a distance of 700 kilometers (430 miles).
Moscow tested TSAR over the wastelands of Novaya Zemlya, a remote island surrounded by the Arctic Ocean, to isolate its effects from the Russian mainland and humanity. All buildings within the test range, both wooden and brick, were destroyed, including the village of Severny located 55 kilometers (34 miles) from ground zero. The thermal pulse would have caused third degree burns at a distance of 100 kilometers (62 miles) and was felt by an observer 270 kilometers (170 miles) from ground zero. Windows and doors were broken at a distance from ground zero of 900 kilometers (560 miles), including in Finland and Sweden.
Even though TSAR was not a ground contact burst, but airburst at an altitude of 4 kilometers (13,000 feet), it caused an earthquake-like seismic shockwave, registering at 5.5, that circled the planet three times.
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