The Soviet RDS-220 hydrogen bomb (code name Ivan or Vanya), known by Western nations as Tsar Bomba (Russian: Царь-бо́мба, tr. Tsar'-bómba, IPA: [t͡sarʲ ˈbombə], lit. Tsar bomb), was the most powerful nuclear weapon ever created. Tested on 30 October 1961 as an experimental verification of calculation principles and multi-stage thermonuclear weapon designs, it also remains the most powerful explosive ever detonated. It was also referred to as Kuzma's mother (Russian: Ку́зькина ма́ть, tr. Kúz'kina mát', IPA: [ˈkusʲkʲɪnə ˈmatʲ]), possibly referring to First secretary Nikita Khrushchev's promise to "show the United States a Kuzma's mother" (an idiom roughly translating to "We'll show you") at a 1960 session of United Nations General Assembly.
The bomb was detonated in secret but was detected by US Intelligence agencies. The US apparently had an instrumented KC-135R (Operation SpeedLight) in the area of the test, close enough to have been scorched by the blast. The bhangmeter results and other data suggested the bomb yielded about 58 megatons, and that was the accepted yield in the literature until the Soviet scientists revealed that their instruments indicated a yield of 50 megatons in 1991. As they had the instrumental data and access to the test site, their yield figure has been accepted as more correct.
In theory, the bomb would have had a yield in excess of 100 megatons if it had included a uranium-238 tamper, but because only one bomb was built, that capability has never been demonstrated. The single bomb was detonated at the Sukhoy Nos ("Dry Nose") cape of Severny Island, part of Novaya Zemlya.