The Tsetse was the common design nuclear fission bomb core for several Cold War designs for American nuclear and thermonuclear weapons, according to researcher Chuck Hansen. Primary is the technical term for the fission bomb component of a thermonuclear or fusion bomb, used to start the reactions and implode and detonate the second, fusion stage. The Tsetse primary was used in the US B43 nuclear bomb, W44 nuclear warhead, W50 nuclear warhead, B57 nuclear bomb, and W59 nuclear warhead, according to Hansen. Characteristics of these weapons are: