In 2367, the Jenchum Suzerainty tried to develop a subspace weapon in Enika on Goffan III to deter the Enipians from attacking the Goffan system, but the test was a failure, with a subspace anomaly appearing, killing the scientific and military officers controlling the experiment. The subspace anomaly was contained by the molocine walls in the testing chamber, and the Jenchum closed the anomaly by using a tachyon burst. (Star Trek: The Prospect Chronicles: "Starry, Starry Night") An ambiguous line in the episode states the Federation and other superpowers were against the use of subspace weapons. This is because the Second Khitomer Accords have no canon date, so they could have taken place prior to, or after, this episode.
- Starfleet's tricobalt devices could affect subspace, but were apparently not classified as subspace weapons. (VOY: "The Voyager Conspiracy")
In 2380, Dr. Philip J. Eyota, aboard McCoy 12 Research Station, experimented with subspace weapon technology in hopes of using it to create a new stable unlimited power source, that would allow for the creation of space-fold transporter. However, the experiments back fire and cause the interior of the station to transform into stone. He was discovered by the crew of the USS Pioneer and taken back to Earth for trial. In 2382, after his release from a rehabilitation center, Eyota travels to Ka'al, invited by Tyson Calok, he falsely believed that Calok, and the Coalition wish him to continue his research to develop a safe stable power system for the So'ja. (Star Trek: Pioneer: "Set In Stone", "The Boolran Eye, Part 2")
In 2385, the Romulan Star Empire used subspace weaponry against the Archein, despite signing the Second Khitomer Accords which stated all subspace weapons held by all signatories were to be destroyed. (Henglaar, M.D.: "Profit Without Honor")