Dreadnought
A dreadnaught is a type of interstellar cruise missile built by the Cardassian Union. The Cardassians used them to attack Maquis worlds. It carries a payload of a thousand kilograms of antimatter, giving it a theoretical yield of over 40 GigaTons.
The Cardassians may have used them to attack Maquis targets in the DMZ without openly violating their treaty commitments. Since a Dreadnaught missile has no crew, it isn't technically a starship, although it does have a maintenance compartment with life support. The missile also has it's own weapons and defenses to prevent interception.
"Dreadnaught," the Voyager episode
B'Elanna Torres reprogrammed one of these missiles that was captured by the Maquis after failing to detonate, directing it to attack a Cardassian world. When the Caretaker brought the device to the Delta Quadrant, it selected Rakosa V -- a nearby planet that resembled its assigned target -- and proceeded to attack. The crew of the USS Voyager was forced to destroy it, but they were greatly hampered by its onboard defenses.
We see Torres's thought processes at work with this device. She used large quantities of advanced technology in a machine designed to blow up, and included a paranoid array of "what if" instructions to keep it from being defused if it were intercepted. Among these scenarios was one in which the Cardassians captured her and brainwashed her into trying to defuse the device for them.