Vulcan defense vessel

From Memory Alpha, the free Star Trek reference.

Vulcan defense vessels were starships assigned to defend the Vulcan system in the 2360s.

In 2368, after the Romulans' attempted invasion of Vulcan using a convoy of stolen T'Pau-type Vulcan transports was discovered, a group of Vulcan defense vessels were sent to assist the USS Enterprise-D in intercepting the ships before they returned across the Romulan Neutral Zone. The convoy was, however, destroyed by a Romulan D'deridex-class warbird before the defense vessels could arrive. (TNG: "Unification II")

Whether these vessels were Starfleet, Vulcan only, or some other organization's is not known. It is also not known whether the ships were a single class of ships or a general descriptive phrase for a fleet of different classes.