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 , was the most powerful weapon in the U.S. nuclear arsenal after the last B41 nuclear bombs were retired in 1976. With its retirement, the largest bomb currently in service in the U.S. nuclear arsenal is the B83, with a maximum yield of . The B53 was replaced in the bunker-busting role by a variant of the two-stage B61 nuclear bomb.