The J3 torpedo (later known as the J47 torpedo) was an experimental torpedo the Dominion tried testing out in 2374. Information on it was taken in by the USS Phoenix-X and for years had been secretly worked on by Lieutenant GoyCho. (Star Trek: Phoenix-X: "The Tiloniam System", "The Tilonian System", "Experimentalism")
In 2374, the Dominion attempted to simultaneously test the torpedo and use it for plans of destruction. A fleet of their ships were able to destroy the Tiloniam system star using the torpedoes. But a few malfunctioning torpedoes were unsuccessful in an attack against the Phoenix-X. ("The Tiloniam System", "The Tilonian System")
The J3 torpedo was finally thought to be completed in 2382 aboard the Phoenix-X. Along with the Romulan starship Caterina, both vessels attempted to test out the torpedoes. A test was successful with the Caterina, but when it came to the Phoenix-X, there was interference by a virus of some sort. The virus eventually renamed the torpedo the J47 torpedo and rendered the whole experiment inconclusive. ("The 47's")
- The torpedo's characteristics are comparable to the tricobalt device.