Unimatrix 01 is a subsection of the Borg Collective. Borg drones assigned here operate in close association with the Borg Queen. Seven of Nine was the tertiary adjunct of Unimatrix 01 until her release from the Collective in 2374. (VOY episodes: "Dark Frontier", "Dark Frontier", "Scorpion, Part II")
During the Borg Invasion of 2381, Federation President Nanietta Bacco attempted to rally an allied fleet to fight off the invading Borg fleet, following USS Enterprise-E Captain Jean-Luc Picard's suggestion to send the force through a subspace tunnel and fight on the Borg's territory. As a member of a Federation think tank, Seven was doubtful of the effectiveness of the plan, but Admiral Hastur had more confidence, claiming it would be easier than attempting an invasion of Unimatrix 01. (ST - Destiny novel: Mere Mortals)
Connections[]
Unimatrix 01 article at Memory Alpha, the wiki for canon Star Trek.