Medical Transport 136 was a Kraylor vessel with a few decks, warp capacity, and armed with phasers.
Medical Transport 136 differed from other Kraylor medical transports by being used on a secret mission by a research team, lead by Lokan, to develop a cloaking device for their fleet. While en route to their homeworld with the specifications, they were ambushed by their enemy, the Anarri. It was only through the intervention of the Delta Flyer that allowed the vessel to survive.
Ensign Harry Kim took command of the starship at Lokan's request and with permission of Voyager's Captain Janeway, where he renamed the vessel Nightingale. (VOY: "Nightingale")