Annorax's temporal weapon ship, which erased entire civilizations from history in his attempt to restore the Krenim Imperium, until Voyager destroyed it.
The Krenim weapon ship was a vast vessel built by the Krenim scientist Annorax to fire temporal incursions, waves that removed a target from the timeline altogether. Shielded by temporal technology, the ship and its crew existed outside the normal flow of time and were unaffected by the changes they caused.
Annorax had spent two centuries trying to restore the Krenim Imperium to its former glory after his first incursion accidentally erased the colony where his wife lived. Each alteration had unexpected consequences, and he had grown obsessed with achieving a perfect timeline in which everything he had lost was restored.
In Year of Hell, Voyager's path through Krenim space brought it into the weapon ship's sights, and months of battle left the starship battered and many of its crew dead. Janeway finally rammed Voyager into the weapon ship, destroying it. With the ship gone, history reset itself, Annorax's first incursion never took place, and Voyager passed peacefully through Krenim space.