An experimental multi-vector assault ship stolen by Romulans and recaptured with Voyager's help.
The USS Prometheus was the prototype of an advanced Starfleet class with a special multi-vector assault mode, in which the ship splits into three sections that can fight independently. It appears in the Voyager episode Message in a Bottle.
Voyager found a network of alien relay stations reaching toward the Alpha Quadrant and used it to send its Emergency Medical Hologram as a data stream to a Starfleet ship. The Doctor arrived aboard the Prometheus, only to find that Romulans disguised as Starfleet officers had seized the ship and killed most of its crew.
The Doctor teamed up with the ship's own Emergency Medical Hologram Mark II, and the two holograms worked to stop the Romulans, at one point triggering the multi-vector mode to fight off a Romulan warbird. With help from arriving Starfleet ships, they retook the Prometheus. The Doctor then returned to Voyager with the news that Starfleet now knew Voyager had survived.