The Silver Carrier was an empty and abandoned rocket that the Cybermen used to infiltrate Space Station W3, hoping to use W3 as a beacon for their invasion fleet. The Second Doctor and Jamie arrived on the ship and were attacked by the servo robot, which was still operating and in charge of the ship, despite it being abandoned. They were then rescued by members of the staff of W3.
Originally a supply ship for Station 5, it was, according to Zoe, discovered nine weeks overdue and 90 million miles off course. The whereabouts of its crew were never determined. (TV: The Wheel in Space)