In the early 1960’s, the Soviet Union designed and tested the Tsar Bomba. It was 26 ft long and 8 ft in diameter – too big to fit within the bomber itself. It released 57 megatons of energy which is more than 1,500 times that of the Hiroshima and Nagasaki bombs combined.
– WTF Fun Facts
Source: http://www.bbc.com/future/story/20170816-the-monster-atomic-bomb-that-was-too-big-to-use