Pursuit 4 was a space bug, an auxiliary vehicle specifically customized for military combat and rescue operations in the 23rd century. In the year 2266, Pursuit 4 was one of three such vessels assigned to the Federation starship USS Enterprise.
History and specifics[]
Space bugs like Pursuit 4 were painted red. They were armed with four phaser cannons, two on the roof of the craft and two attached to the forward hull. They had three rear engines and three atmospheric stabilizer fins.
In 2266, Spock ordered Pursuit 4 and Pursuit 7 to provide cover fire while Space Rescue Bug 5 retrieved captives from a disabled Agonite space eagle. (TOS comic: "The Eagles Have Landed")