The renegade Borg ship.
In late 2369, a group of rogue Borg began attacking Federation outposts and colonies in several outlying sectors with a new type of vessel. Starfleet designated this vessel the Borg Type 03, also informally known as the rogue Borg ship. This unusual design was asymmetrical and totally unlike the previously encountered Borg cube. However, the vessel was still heavily armed and massively armored, and capable of great destructive power.
Only one ship of this type has been observed; the ship attacked the research outpost on Ohniaka III, as well as the MS-1 colony, using previously-unknown transwarp conduits to appear suddenly over the target and launch a quick attack. In both cases it confronted the USS Enterprise-D, which responded to the colonies' distress signals. The Enterprise then followed the Borg ship through the conduits to locate their base of operations. (TNG: "Descent, Part I")
A graphic showing the designation of the ship.
As numerous Enterprise personnel searched the surface of the unnamed world for the missing Commander Data, a deadly game of cat-and-mouse played out in orbit. The Borg ship attacked, forcing the Enterprise, under the temporary command of Doctor Beverly Crusher, to flee to the edge of the star system. However, Crusher determined to retrieve the remaining crew who had been left behind, and returned to the planet, evading the Borg ship's attack long enough to retrieve most of the remaining personnel. However, the Enterprise delayed long enough that its warp drive was crippled by the Borg ship. Forced to flee again, but this time restricted to impulse speeds, Crusher ordered the Enterprise to activate an experimental metaphasic shield that allowed the ship to enter the nearby star's corona, where the Borg ship could not follow.
The Borg ship held position outside the corona, waiting for the Enterprise to emerge. However, the Enterprise used a particle beam to cause a solar flare that completely engulfed the Borg ship, destroying it. (TNG: "Descent, Part II")
Background
Rogue Borg ship in a pinball machine.
The design for the Rogue Borg ship was later reused to represent a display for a Borg multi-kinetic neutronic mine in VOY: "Scorpion, Part II".
The "Type 03" designation is visible on a monitor in "Descent, Part II".
This design was designated as the "Borg Assimilator Class" vessel in the PC game Star Trek Armada 2.
A mirrored version of this ship was used as a centerpiece in the Star Trek: The Next Generation pinball machine.