Ultritium 342 was a high yield version of the standard industrial ultritium. This explosive was used in terraforming applications and large scale excavations. It was activated by a microwave pulse ignition device. In situations where nuclear explosives were not desirable, this explosive was the preferred choice. In 2367, this explosive was stored on aboard the Federation starship USS Enterprise-D.
In that year, Ultritium 342 was on a list of explosives that Lieutenant Commander Data and Counselor Deanna Troi searched through in an attempt to find one that could produce enough energy to release the USS Enterprise-D and an alien ship from the Tyken's Rift. (TNG: "Night Terrors")