In early 2377, tactical cube 138 was engaged by the starship USS Voyager in which Captain Janeway, Commander Tuvok, and Lieutenant Torres beamed aboard to deploy a nanovirus into the cube's central plexus. As part of the plan, the away team was assimilated into the Collective, while the virus worked to separated the members of Unimatrix Zero from the hive mind.
In the end, the Borg Queen initiated the self-destruct sequence for Tactical Cube 138 in an attempt to kill Janeway, Tuvok, and Torres. The starship USS Voyager, however, beamed them away just before the cube's destruction. (VOY: "Unimatrix Zero", "Unimatrix Zero, Part II")