The Delta Rana warship was an illusory starship created by the Douwd who had taken the form of Kevin Uxbridge. He used the illusion as a form of planetary defense system for Rana IV against the USS Enterprise-D. (TNG: "The Survivors") It was noted to have five times the mass of the Enterprise.
In 2366, when the USS Enterprise-D was investigating the destruction of the Federation colony on Rana IV, Kevin created this illusory warship in orbit of Rana IV in an attempt to force the Enterprise to leave the planet, and his home. This class of warship wasn't listed 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 Rana colony.
Initially this illusory vessel fired jacketed streams of positrons and antiprotons, an equivalent firepower of 40 megawatts, which caused no damage to the Enterprise. The Enterprise fired a warning shot at the ship, causing it 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. (TNG: "The Survivors")
Kevin made the ship reappear, some time after the Enterprise had returned to Rana IV. During its second appearance, the warship looked to the crew of the Enterprise to be much larger and much "meaner." 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 only superficial damage to the ship, but effectively taking down its shields. A second shot took out the rest of the Enterprise's 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 warship, but caused no damage to it. It was then determined that the warship's defenses were able to absorb any incoming weapons. The warship returned fire, taking out the Enterprise's shields and weapon systems control, as well as causing some internal damage to the ship and non-fatal injuries to sixty-six members of the crew. (TNG: "The Survivors")
When the Enterprise returned for a third time, Picard told Kevin that the Enterprise would stay in orbit to protect Kevin as long as the threat from the warship remained. Kevin had the warship appear for a third time. This time, the Enterprise kept its distance and 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, destroying it.
Picard had determined that the warship was directly serving the needs of Kevin Uxbridge to bait and later chase the Enterprise away from the planet. Kevin Uxbridge confirmed the assumption, and indicated that he had tried the same diversionary tactics on the Husnock warship, also to no avail. (TNG: "The Survivors")
The script notes for the episode indicate that the ship created by "Kevin" was a recreation of the Husnock warship that destroyed the colony. The Star Trek Encyclopedia (3rd ed., p. 199) 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 Star Trek: The Next Generation Companion (3rd ed., page 103), "The Husnock warship, built by Tony Meininger, 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." It was Meininger's first involvement with the Star Trek franchise (and his only one for TNG, albeit as an outside contractor), before moving on to become the main supplier of studio models for televised Star Trek starting with DS9: "Emissary"
In this episode, the model of the ship was modified slightly for the second appearance: a third weapon spike was added to the underside of the ship, so the ship did look "meaner" the second time.