The D'Kyr was a Vulcan D'Kyr-type combat cruiser that was in service with the Vulcan High Command in the mid-22nd century.
Enterprise was supposed to rendezvous with the D'Kyr when its mission was canceled in March 2152. Subcommander T'Pol and Doctor Phlox were to be dropped off on the D'Kyr for transport home.
When Enterprise failed to make the rendezvous, the D'Kyr monitored the encounter between Enterprise and several Suliban cell ships. After escaping the Suliban helix, Enterprise managed to make the rendezvous, and Captain Jonathan Archer convinced the Starfleet Command Council to allow his ship's mission to continue. (ENT: "Shockwave, Part II")