15. Romulan Warbird
The late-24th century Romulan warbird makes its first appearance at the climax of "Remembrance", emerging from a nebula before parking itself inside the Borg Artifact.
Much smaller (judging by the cockpit window) than previous warbirds, this ship looks a bit like a Romulan scout ship, but is designated as a "warbird" in behind-the-scenes footage from CBS All Access' Ready Room. Despite its prominence in the closing scene of episode one, we never got to see this warbird in action as it was more or less replaced by larger counterparts in later episodes.
Still the 2390s Romulan warbird appears in "Remembrance", "Maps and Legends", "Nepenthe", and even deep in the background in "Broken Pieces".