A class-4 tactical cube, a heavily armed vessel with its Central Plexus protected by multi-regenerative security grids. Tactical Cube 138 was infiltrated by U.S.S. Voyager crew members who attempted to introduce a virus into the Collective through its Central Plexus, in a plan to help the occupants of Unimatrix Zero reassert their individuality in the physical world. Once the Borg Queen understood the nature of that plan, she initiated a self-destruct sequence for the cube, in hopes of stopping the virus and destroying Voyager. The cube blew up with a massive shock wave, but Voyager and its crew escaped harm, and a resistance movement bent on undermining the Collective was set into motion.