Enhanced fusion was a type of nuclear fusion technology, also called "super-atomic" by Human researchers. Enhance fusion was extremely dangerous; the use of this technology had destroyed the civilization of Delphi Centaurus VI sometime prior to the mid 20th century.
In the 1960s, the United States government initiated Project Hercules, a top secret effort to develop enhanced fusion technology for military use. By late 1968, an enhanced fusion bomb had been built, and was prepared for test detonation. Aegis agent Gary Seven noted that such a test could potentially shroud half of the country with radiation if anything went wrong. (TOS - Star Trek: Assignment: Earth comic: "Brighter Than a Thousand Suns")