Borg sphere

The Borg sphere is a huge sphere-shaped starship used by the Borg Collective, sometimes designated as a long range tactical vessel. (VOY: "Drone")

At least one Borg Sphere has been observed to have time travel capabilities. On one such occasion, a Borg Sphere travelled back to the year 2063, in order to prevent the historical event known as First Contact. (Star Trek: First Contact)

During Voyager ' s attempt to get home in 2378, they were chased by Sphere 634, one of the few the Borg Queen had managed to keep in contact with. The sphere managed to weaken Voyager inside the collapsing transwarp corridors before capturing the ship. When the sphere arrived in the Alpha Quadrant, a fleet of 27 Federation starships opened fire on the sphere. It took a transphasic torpedo fired from Voyager to defeat it. (VOY: "Endgame")