W41

The B-41 (also known as Mk-41) was a thermonuclear weapon deployed by the United States Strategic Air Command in the early 1960s. It was the most powerful nuclear bomb ever developed by the United States, with a maximum yield of 25 megatons of TNT (100 petajoules). A top secret document (DCI Briefing to the JCS, 30 July 1963), states "The US has stockpiled bombs of 9 MT and 23 MT..." which would likely be referring to the B-41's actual yield(s). The B-41 was the only three-stage thermonuclear weapon fielded by the U.S.