Boosted fission devices were a major innovation in the development of nuclear weapons. By placing a deuterium-tritium core inside of a plutonium pit, designers could use fission to cause fusion, which in turn causes greater fission. The result is a much stronger and more efficient weapon without the need for additional fissile material. It also served as a stepping stone to a true hydrogen bomb. Photos of TVA power plant is licensed under CC 2.0: https://creativecommons.org/licenses/by-sa/2.0/