The IRW Tiamatra was a Romulan starship of a warbird type active in the late 24th century.

When the Borg invasion became critical, the Tiamatra was one of the vessels to amass at the Azure Nebula. While there, it worked to determine the proper soliton wave frequency to open subspace tunnels twenty-five and twenty-seven, along with the Klingon ship IKS Chorbog. However, seven thousand Borg cubes attacked from their tunnel, completely obliterating the allied fleet. (ST - Destiny novel: Mere Mortals)

Although unspecified, it can be assumed but not determined that the Tiamatra was a Romulan warbird. Since it was not specified, it is unknown if it was loyal to the Romulan Star Empire or the Imperial Romulan State.