Most modern weapons are fission-fusion-fission designs with the latter fission step using neutrons from the preceding fusion step. Most of the energy in most "H

Most modern weapons are fission-fusion-fission designs with the latter fission step using neutrons from the preceding fusion step. Most of the energy in most "H-bomb" designs comes from fission: https://en.wikipedia.org/wiki/Thermonuclear_weapon https://en.wikipedia.org/wiki/Thermonuclear_weapon A notable example where this wasn't the case was the test of the Tsar Bomba where the final fission component was left out largely because of the enormous amount of fall-out this would create - reducing the yield from 100Mt to 50Mt. The resulting explosion did have a very high fusion component.