Krenim temporal weapon ship
Weapon ship destroyed by Voyager in 2374. The ship was created by Krenim scientist Annorax, who was attempting to restore the Krenim Imperium.
The ship operated outside of regular space-time, and had the ability to erase an object and all of its influence throughout history. Annorax first used the ship to destroy the Krenim's greatest enemy, the Rilnar — unfortunately, this also destroyed an important antibody in the Krenim genetic structure. Fifty million Krenim died of the disease as a result. Annorax continued to use the weapon ship in an attempt to restore his people, and in doing so, wiped out many species.
The damage was finally reversed when Voyager destroyed the weapon ship, restoring the timeline.