High Quality Content by WIKIPEDIA articles! 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 of TNT (38 PJ), was the most powerful weapon in the U.S. nuclear arsenal after the last B41 nuclear bombs were retired in 1976.