Borg Tactical Cube
From Star Trek : Freedom's Wiki
The Borg Class 4 Tactical Vessel was a type of heavily armed Borg Cube utilized by the Borg Collective. The tactical cube differed from the standard Borg cube in several ways, the most notable being the extensive hull armor that covered a large portion of the exterior hull of the ship. The interior was also slightly altered from what is known of Borg 'architecture'. The vessel's Central Plexus was protected by multi-regenerative security fields.
Only one such vessel was observed by Starfleet – by USS Voyager in 2376. The tactical cube was caused to self-destruct by the Borg Queen during a brief civil war within the Collective. (VOY: "Unimatrix Zero", "Unimatrix Zero, Part II")
