The VSS ShiKahr was a Vulcan starship of an alternate timeline in service during the mid-23rd century. The alternate timeline in which the ShiKahr existed was the result of the Romulans' Second History project, which interfered in the timeline at a key moment in Human history.
The ShiKahr was an alternate version of the USS Enterprise (NCC-1701), and a number of crew members from the Enterprise of the original timeline served on board the ShiKahr. This included Spock (who was the ship's captain), Pavel Chekov (the first officer), Doctor Leonard McCoy, and Montgomery Scott. James T. Kirk also served on the ShiKahr, and was a disgraced ensign whose promising career had been sidelined when he was found guilty of a murder during his time at the Starfleet Academy. In this timeline, Christopher Pike had previously served as first officer of the ShiKahr under Spock for a number of years before becoming captain of the VSS T'Ruda, one of the first humans of this timeline to be given his own command.
By the mid-23rd century, the Romulan interference in the time line had begun to cause the universe to collapse in upon itself, with a number of highly ranked officers going insane in the process. Captain Spock and Ensign Kirk traveled back in time and were successfully able to prevent the interference, preventing the time line from occurring and restoring history to its original shape. (TOS novel: Killing Time)