Explanation: GMT=Greenwich Mean Time, lat/long=latitude and longitude, HOB=height of burst above ground/water surface (negative height indicates depth below surface), % fission=percentage of yield from fission, notes includes crater diameter if applicable, "barge" indicates detonation on off-shore barge, "experimental" indicates device not closely related to a warhead design. See text for sources.

The 30 October test was that of the RDS-220 and was the highest yield nuclear detonation ever conducted. The largest nuclear weapon ever developed by any nuclear power was the Soviet RDS-220,[14] also nicknamed "Big Ivan", "Vanya" or "Tsar Bomba" (King of Bombs). It was a three-stage weapon weighing 24.8 metric tons and was 8 meters long. Its 2-meter diameter required a specially modified version of the Tu-95 Bear bomber for delivery. The single such Tu-95V carried the RDS-220 partially protruding from the bomb bay.[15, 16] The U.S.S.R. tested this design in an airdrop over Novaya Zemlya on 30 October 1961 at a yield of about 58 megatons.[17, 18, 22] However, this was a reduced yield "clean" version: the uranium sleeve on the tertiary stage was replaced with lead, and the fission yield was only 3% of the total yield.[15] The full yield version had a yield variously reported as 100 mt [16] or 150 mt [14]. About 80% of the fallout from the "Tsar Bomba" test was deposited as global fallout.[19]

Some sources report the burst altitude as 3500 m[12], while Russian sources give the burst altitude as 4000 m[20]. It was dropped from the Tu-95V bomber from an altitude of 10,500 m by parachute, allowing the bomber to reach a distance of 45 km before detonation. Reportedly buildings were damaged by the blast "hundreds of kilometers" from ground zero.[21]

The yield of the 30 October 1961 test remains the subject of some debate. Best estimate here is that the actual yield was 57-58 mt, based on the following:

• The U.S. estimate of 57-58 mt was based on bhangmeter (high-speed photometer) observations and other data from a USAF KC-135 flown near the blast--apparently to within 45 km--as analyzed by the Foreign Weapons Evaluation Panel (or Bethe Panel) to determine the yield.[15, 23, 24]
• A yield of 58 mt has been affirmed in scientific publications by Russian experts on the Soviet testing program.[29]
• Nikita Khrushchev in his memoirs claims that the device yield was estimated before the test as 50 mt, and that the actual yield proved greater at 57 mt.[26]
• Following the collapse of the Soviet Union, official Russian sources (e.g. the Russian atomic energy ministry) have released information on Soviet nuclear tests, reporting a yield of 50 mt.[20, 25] In many cases, discrepancies between the new Russian data and older Western estimates represent the large uncertainties involved in Western intelligence efforts to estimate yields from remote observation. In this case the U.S. data was acquired from close at hand (sufficiently close that the U.S. KC-135 suffered scorching on the fuselage from the flash[23]). Discrepancies with Russian data may represent continued Russian secrecy (e.g. exact yields for several high yield Soviet tests are still unannounced by Russia [20]), combined with the desire to minimize the issue of fallout associated with the test. The current Russian figures for the Tsar Bomba test, 50 mt yield at 4000 m altitude, place it safely 9% above the Russian agency's threshold defining "air explosions," where "the expanding fireball does not touch the ground surface" [27], whereas the Western data of 57-58 mt yield at 3500 m altitude place it 9% below this threshold.

The 1962 test series included up to eight tests over 4 mt (the yield of several are uncertain). These high yield tests were all conducted at Novaya Zemlya. MINATOM-reported burst height and yield and Western yield estimates are:

• on 5 August, 3600 m altitude, 21.1 mt (MINATOM) or 30 mt (Western);
• on 25 August, 2980 m altitude, 1.5 to 10 mt (MINATOM) or several mt (Western);
• on 27 August, 3000 m altitude, 4.2 mt (MINATOM) or 14 mt (Western);
• on 19 September, 3280 m altitude, 1.5 to 10 mt (MINATOM) or 20 mt (Western);
• on 25 September, 4090 m altitude, 19.1 mt (MINATOM) or 25 mt (Western);
• on 27 September, 3900 m altitude, over 10 mt (MINATOM) or less than 30 mt (Western);
• on 22 October, 3230 m altitude, 8.2 mt (MINATOM) or several mt (Western); and
• on 24 December, 3750 m altitude, 24.2 mt (MINATOM) or about 20 mt (Western).[12, 13]

The 19 September and (probably) the 27 September tests were competing designs for a high-yield warhead, probably for ICBM delivery. Andrei Sakharov describes his unsuccessful efforts to stop the test of the competing design on the grounds that it would unnessecarily increase global fallout.[28] The last multimegaton test, that on 24 December, was a reduced yield version of the Chelyabinsk high-yield weapon design (yield of the full-yield version was 50 mt).[12, 25]

Two high yield tests were conducted underground at the southern island of Novaya Zemlya in 1973. At least one probably exceeded 4 mt in yield. The yield of these and other Soviet underground tests were the subject of debate in the West for years, with some sources suggesting that published yield estimates were too high. Based on recent information from Russian sources, it appears if anything that the Western estimates had been too low. MINATOM has reported a total yield of 7.8 mt for the two 1973 tests at Novaya Zemlya. The first test, on 12 September, involved a salvo detonation of one device reported as 1.5 to 10 mt in yield plus two with yields between 0.15 and 1.5 mt. The total yield for this test was about 4 mt. The test on 27 October is reported by MINATOM as between 1.5 and 10 mt in yield. Western estimates have ranged from 2.8 to 4.9 mt; recent reports place the yield at 3.5 mt. If this is correct, the 12 September test yield was about 4.2 mt, of which about 3-3.5 mt was the larger device.[12, 13, 25, 30, 31, 32] Both tests were probably reduced yield versions of warheads for ICBMs nearing deployment.