In 2375, when she was the night shift helmsman, they answered a distress call. The bio-neural circuitry of the weapon was malfunctioning and it believed itself to be an organic being, claiming it could not remember what its mission was. After the ship's holographic doctor beamed it to sickbay, the device suppressed The Doctor's programming and took control of his holomatrix. It then revealed its purpose and demanded that Captain Kathryn Janeway take it to its target or it would destroy Voyager.
After unsuccessful attempts to deactivate or reason with the weapon, Ensign Harry Kim discovered that the warhead was one of a small contingent that had, in fact, been ordered to stand-down by the Strategic Control Matrix. After successfully convincing the weapon's AI of the validity of its orders, Kim and the AI attempted to convince the other warheads of the mistake. However, since they had passed the two light year threshold after which nothing could cancel the attack, the AI requested that it be beamed out to join the others, reflecting that it was simply completing its mission to protect its people even if the target had changed. Voyager released the weapon and, after it and its fellows had gone to warp, it detonated itself among the remainder of the malfunctioning warheads, destroying them all.
She thanked Harry Kim on behalf of the junior staff for saving the ship from the Druoda warhead, a sentient alien missile that had taken over The Doctor's holo-program. Kim asks her to do him a favor, no more distress calls tonight. (VOY: "Warhead")