A Federation freighter that suffered a catastrophic engine failure near Turkana IV in 2367, forcing its two crew into an escape pod that came down in the lawless colony below.
The USS Arcos is a small Federation freighter with a crew of two. In the episode Legacy, set in 2367, it sends a distress call after its engines fail close to Turkana IV, the collapsed colony where Tasha Yar was born.
The Enterprise arrives too late to save the ship, which explodes, but its two crewmen reach the surface in an escape pod. They are seized by the Alliance, one of the two armed factions that rule the colony's underground city.
The effort to free them brings the Enterprise crew into contact with the rival Coalition and with Ishara Yar, Tasha's sister, who offers to guide a rescue party while pursuing an aim of her own.