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") The torpedo technology itself was uninstalled from the Phoenix-X in 2383. The Captain sent its schematics to Starfleet Corps of Engineers under an anonymous identity. ("Transphasic Meltdown")