This unusual design was asymmetrical and totally unlike the previously encountered Borg cube and Borg scout ship, causing Captain Jean-Luc Picard to speculate whether it was something they had constructed, or an alien vessel that they captured and assimilated. Whatever its origins, the vessel was still heavily armed and massively armored, as direct phaser and photon torpedo strikes from a Galaxy-class starship caused no damage to the ship.
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")
As numerous Enterprise personnel searched the surface of the unnamed world for the missing Lieutenant 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 resolved 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 fusion eruption that completely engulfed the Borg ship, destroying it. (TNG: "Descent, Part II")
The designation "Type 03" was visible on a tactical scan analysis appearing in "Descent, Part II". This classification is presumably because this was the third class of Borg starship design encountered by Starfleet (after the cube and the scout ship). The authors of the Star Trek Encyclopedia (2nd ed., p. 50) identified it as the "Type-2 Borg ship".
This design was designated as an "Assimilator" in the PC game Star Trek: Armada II. This a reference to its in-game special weapon, that can assimilate the crew members of a target and add them to the player's or computer's own crew reserves.
In the novel Greater than the Sum and in Star Trek Online's "Delta Rising" expansion, Hugh commands one of these vessels, christened the Liberator, under the auspices of the Cooperative. In the game, the ship class is called a "Type 03 Command Vessel", the most powerful class of vessel used by the Cooperative. The ship became available to players in February 2020 as the "Liberated Borg Command Juggernaut", obtained from the "Borg Lock Box".