Cobalt is a chemical element with the symbol Co and atomic number 27. Cobalt is a ferromagnetic metal. It is a naturally-occurring element, and was commonly found in a number of ores. Cobalt was used in numerous alloys, and some cobalt-based materials were also used in weapons.
The Lysian Central Command space station was armed with thirty-nine cobalt-fusion warheads. (TNG: "Conundrum") Other military uses of cobalt included cobalt-thorium devices, cobalt bombs, and the nerve agent cobalt diselenide. (DS9: "The Maquis, Part I", "For the Uniform"; TOS: "Obsession")