The T'Pau (NSP-17938) was a Vulcan Mahl'kom group Apollo-class transport that was in service with the Vulcan National Merchant Fleet in the mid-24th century. T'Pau was named in honor of the Vulcan matriarch T'Pau.
The T'Pau was decommissioned in 2364, and was later sent to Surplus Depot Z15 at Qualor II, where it was registered on stardate 41334.2, and stationed at Section-18-Gamma-12. At that time, it was stripped of materials, armaments and sensors, its navigational deflector array being routed to the holding vessel USS Tripoli. During this, a file was created for this ship and stored in the Qualor II Depot Z15 Inventory Database.
In 2368, the array was found in debris from a Ferengi cargo ship. Upon investigation at Qualor II, it was discovered that the ship had been stolen from its resting place in the surplus depot by a Ferengi arms dealer named Omag, who transferred it to a Barolian freighter near Galorndon Core. The Barolians later transferred it to the Romulans, who in turn, refurbished the vessel and used it as part of a "peace" envoy, a ploy used by the Romulans in their failed attempt to conquer Vulcan. The ship was later destroyed by a Romulan warbird to prevent the crew of the USS Enterprise-D from taking custody of it and the Romulan troops aboard. (TNG: "Unification I", "Unification II")
For the remastered episode, the vehicle id had been changed from NSP-17938 to NSP-17938 (Mahl'Kom Group). 
It was the second time, following the appearance of the long range shuttle Surak in Star Trek: The Motion Picture, that a Vulcan ship was seen on screen. (ENT Season 3 Blu-ray, "Impulse" text commentary)