The Delta Rana warship
The Delta Rana warship was a vessel created by the Douwd who took the form of Kevin Uxbridge. He had the ship appear in orbit of Delta Rana IV, the planet on which he lived. This warship did not appear in the Federation vehicle classification index, but at the time it was assumed to be the same Husnock warship which had previously attacked and obliterated the Delta Rana colony.
While the USS Enterprise-D was investigating the destruction of the colony on Delta Rana IV, the Douwd created this warship in attempt to force the Enterprise to leave the planet, and his home.
Firing streams of positrons and antiprotons.
Initially this recreated vessel fired jacketed streams of positrons and antiprotons, an equivalent firepower of forty megawatts, which caused no damage to the Enterprise. The Enterprise fired a warning shot at the ship, causing the ship to retreat from the system. The Enterprise attempted to pursue but was unable to close the gap between the two vessels, even after increasing velocity to Warp 9.37.
The ship later reappeared, some time after the Enterprise returned to Rana IV. During its second appearance, the warship looked to the crew of the Enterprise to be much larger and much "meaner."
The Delta Rana warship (upgraded configuration)
The Enterprise attempted to hail the ship to warn it to stay away from the planet. In response, the ship fired four hundred gigawatts of particle energy at the Enterprise, causing superficial damage to the ship, but effectively taking down its shields. A second shot took out the rest of the Enterprises shields and caused thermal damage to the hull. Ship sensors, however, were able to determine that the warship was in possession of enormous energy reserves, capable of striking with far more powerful bursts.
Following the second attack, the ship moved into orbit of Rana IV and assumed a position over the Uxbridge residence. The Enterprise fired a full phaser and photon torpedo barrage at the ships, but caused no damage to the warship whatsoever. It was then determined that the warships defenses were able to absorb incoming matter and energy. The warship returned fire taking out the Enterprise's shields, its weapon systems control as well as causing sixty-six casualties and some internal damage. Once the Enterprise began to limp away from the planet, the warship again left the system.
The unclassified warship would finally make a third appearance in the system. The Enterprise, which was now keeping its distance, allowed the warship to once again enter orbit over Rana IV -- at which time it destroyed the Uxbridge residence. Following the attack, the Enterprise fired a single photon torpedo at the warship, successfully destroying it.
Picard later determined that this warship was created by Kevin Uxbridge to bait and later chase the Enterprise away from the planet. Kevin Uxbridge confirmed this assumption, and indicated that he had tried the same diversionary tactics on the Husnock warship, also to no avail. (TNG: "The Survivors")
Background
The script notes for the episode indicate that the ship created by "Kevin" is a recreation of the Husnock warship that destroyed the colony. The Star Trek Encyclopedia as well as the Star Trek: The Next Generation Companion also support the supposition that this vessel was intended to be a Husnock ship.
This vessel was designed and built by Tony Meininger. According to the TNG Companion, "The Husnock warship...was one of the first not designed by a member of the TNG art staff. 'Usually there just isn't time to put into designing them if they're just a 'ship-of-the-week' that's going to be re-dressed later anyway,' said Rick Sternbach, adding that decisions on re-use are made by the alternating TNG visual-effects teams headed by Dan Curry and Rob Legato and their model contractors."
In this episode, the model of the ship was modified slightly for the second appearance: one weapon's spike was added to the underside of the ship, so the ship did look "meaner" the second time.