In 2366, the Romulan scout ship Pi crash landed on Galorndon Core, inside Federation space, while conducting an unspecified covert mission. The Pi was destroyed with an ultritium explosive after the crash to prevent its capture by Starfleet. (TNG: "The Enemy")
A few weeks later, another scout ship was encountered crossing the Neutral Zone by its occupant, Admiral Jarok, who used his vessel to defect to the Federation. Following a pursuit across the Neutral Zone from a Romulan Warbird, Jarok, too, destroyed his ship to prevent its capture by Starfleet. (TNG: "The Defector")
The Romulan scout ship was green, with a "bird of prey" look. It has the same basic shape as the much larger D'deridex class warbird.
Very little is known about the capabilities of these vessels, including whether or not they were equipped with cloaking devices, but they were equipped with deflector shields.
The Romulan scout ship, which was initially created for its single appearance in the episode "The Defector", was the last Romulan ship model built for Star Trek until the Romulan shuttle in the Star Trek: Deep Space Nine episode "In the Pale Moonlight". For more information on this studio model, see TNG studio models.
In Star Trek: Armada and its sequel, the Romulan scout ship was named as being of the Talon-class. Additionally, vessels of this type are listed in the Starships expansion volume of Decipher's Star Trek Roleplaying Game as Theta-class shuttle/surveyors. The Decipher Star Trek CCG, however, refers to the class as the Lanora-class scout. None of these designations have been used on-screen, therefore they cannot be considered canon.