Tsar Pushka, the Imperial Cannon, at the Moscow Kremlin
Tsar Pushka (Царь-пушка in Russian) is a huge cannon, founded in 1586 by a Russian founding master Andrey Chokhov. Weight - 40 tons, length - 5,34 m, calibre - 890 mm. This cannon was meant to defend the Kremlin in times of war, but it had never been used. It is decorated with reliefs, including the one depicting tsarFedor Ivanovich on a horse. The carriage was made in 1835. The cannon is placed inside the Moscow Kremlin next to the Tsar Kolokol.
This three stage weapon was actually a 100 megaton bomb design, but the uranium fusion tamper of the teritiary (and probably secondary) stage(s) was replaced by one made of lead to eliminate fast fission by the fusion neutrons.
The nickname Tsar Bomba is a reference to the Russian proclivity for making gigantic but useless artifacts for show.
The world's largest bell (the Tsar Kolokol) and cannon (the TsarPushka), neither of which are actually useful for anything, are on display at the Kremlin.
The Tsar Bomba was too large to fit entirely within the bomb bay of the Tu-95, the largest Soviet bomber of the day.
The Tsar Bomba was the culmination of a series of very high yield thermonuclear weapons designed by the USSR and USA (e.g., the Mark-17[2] and B41) during the 1950s.
Soviets restarted their tests two months before Tsar Bomba, and there was no de-jure moratorium in place at the time (the USA had already announced that it considered itself free to resume testing after further notice).