A Vulcan defense vessel was a type of starship assigned to defend the Vulcan system in the 2360s. In 2368, after the Romulans' attempted invasion of Vulcan using a convoy of stolen Apollo-class 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" )