<P> Fission: 100% oralloy </P> <Tr> <Th> Blast yield </Th> <Td> 9 megatons </Td> </Tr> <P> The Mk / B53 was a high - yield bunker buster thermonuclear weapon developed by the United States during the Cold War . Deployed on Strategic Air Command bombers, the B53, with a yield of 9 megatons, was the most powerful weapon in the U.S. nuclear arsenal after the last B41 nuclear bombs were retired in 1976 . </P> <P> The B53 was the basis of the W - 53 warhead carried by the Titan II Missile, which was decommissioned in 1987 . Although not in active service for many years before 2010, fifty B53s were retained during that time as part of the "hedge" portion of the Enduring Stockpile until its complete dismantling in 2011 . The last B53 was disassembled on 25 October 2011, a year ahead of schedule . </P>

What is the largest nuclear bomb america has