The Vector was a type of Imperial-class Star Destroyer. This vessel belonged to the Imperial Navy and was in operation before the Battle of Yavin took place.
Acting on the orders of Darth Vader, the ship journeyed to the planet Meglumine in 1 BBY with its crew. Their mission was to obtain materials connected to the Blackwing virus. The plan was to transport these materials to a testing site on the planet Khonji Seven. However, while the ship was in transit within the Mid Rim, one of the tanks containing the virus broke open. This resulted in the infection of most of the crew, turning them into mindless creatures. The Vector carried at least 46,700 Imperial individuals, including 9,700 stormtroopers. Almost all of them perished due to the virus. A group of thirty, among them Commander Gorrister, isolated themselves in a section of the ship, seeking refuge in the Freebird shuttle.
The Purge, a prison barge, encountered the Vector ten weeks later, after experiencing engine trouble. A team from the Purge, headed by Captain of the Guard Jareth Sartoris, boarded the Vector to recover parts from the ship's engines. However, within hours of the team's return to the Purge, the majority of the barge's population also became infected with the virus. With the barge crippled and escape impossible, the prison ship's survivors boarded the Vector, hoping to use it as a means of escape. Of the six survivors who transferred from the Purge to the Star Destroyer, four managed to escape.
The novel Death Troopers, authored by Joe Schreiber, primarily takes place on the Vector. While the ship's name isn't mentioned in the novel, it is revealed in the in-universe Twitter account of an Imperial stormtrooper, which was created before the book's release. The account details his experiences aboard the Vector leading up to the events described in the novel.
The name Vector is likely derived from the epidemiological term that refers to an organism that carries a disease-causing agent.