The Stornoway-class of Advanced Destroyers was a one-off experimental modification of a Rota-class destroyer, the EFS Stornoway. The Chemlaser and Blackhawk Missile launchers from the Rota-class were removed and replaced by an experimental weapons system known as a Graviton Cannon.
This device was an attempt to produce a far smaller version of a Gravitic Ram or Grav Lance, and was basically a super-sized Tractor Beam emitter. It produced a focused beam of asymetric gravity waves, pushing and pulling the bits of a target in different directions with gravity fields tens of thousands of times stronger than that of Earth. This tore apart starships and asteroids, although the effective range was very short. To compensate for the loss in point defense due to the elimination of the Blackhawk Missile tubes, the midships ring of Plasma Phalanxes were replaced by more powerful and longer-ranged Particle Phalanxes.
The EFS Stornoway completed modifications in 2242, and its test cruise was captained by Erich Von Shrakenberg, and the weapon was first fired by tactical officer Herbert Gergenstein. Despite successful tests, the short range was not judged to be effective enough to justify the high cost of the weapon system, and the program was cancelled. No other ships were ever modified in this way. The Stornoway continued in commision throughout the Third Civil War, but was sent to the scrapyard in 2250. The Graviton Cannon was apparenty salvaged at some point and attached to a corvette, but when it was used in an Imperial Fleet raid on the Elysia system in 2265, the second time it was fired, it malfunctioned and blew out the artificial gravity system on the ship, killing the entire crew.
Behind the Scenes
The EFS Stornoway was the very first ship Martin Hohner designed for this game, specifically as the vessel of his Season 4.2 character Eric Von Shrakenbeg. The Graviton Cannon concept was something he came up with for a Star Trek fanfic he never got around to writing, and the pulse-fusion drive was based on Project Orion and the ships seen in The Stone Dogs by S.M. Stirling. The other weapons systems on this class have gone through several retcons as the wider technobabble of this universe was more firmly established.