An early draft of Star Trek III had Commander Kruge stealing a Romulan ship for his quest against Kirk.
'The bird-of-prey was originally established to be Romulan in 'Balance of Terror' (TOS). Possibly the strangest ship in all of Star Trek history, the Klingon Bird of Prey is one of the most commonly seen Klingon vessels - yet it was originally meant to be a Romulan ship! As the Encyclopedia explains.
