Husnock warship that harassed the Enterprise-D at Delta Rana IV, actually an illusion created by the grieving Douwd Kevin Uxbridge.
The Husnock warship appeared over the devastated Federation colony on Delta Rana IV in The Survivors. It attacked the Enterprise-D and then fled faster than the starship could pursue, returning whenever the crew lingered near the planet.
The vessel was not real. It was a projection created by Kevin Uxbridge, a powerful being known as a Douwd who had lived among the colonists as a human. When the Husnock wiped out the colony and killed his wife, Kevin destroyed every Husnock in existence in a moment of rage, and he used the phantom warship to drive visitors away from his secret.