The Romulan Bird of Prey was designed by Wah Ming Chang in just two weeks’ time. He also built a small model of the ship although it isn’t clear if this was the same as the internally lit studio model that was sent to Film Effects of Hollywood where the footage was shot and used in both the episodes “Balance of Terror” and “The Deadly Years.”
Wah’s contributions to Star Trek were largely unknown at the time. He worked for the show independently from his home studio in Altadena, California. Due to union complications and restrictions, he wasn’t credited on screen even if Wah supplied most of props and many costumes, including the Romulan helmets in “Balance of Terror,” for The Original Series.
Producer Robert Justman, who considered Wah’s work superior to anything members of the propmakers’ union came up with, invented a ruse to make it appear that Wah’s creations were bought for the show off the shelf. His true involvement in the making of Star Trek only became known a decade after it first aired.
After filming, the Bird of Prey model disappeared which may account for the Romulans showing up in Klingon D7 cruisers in the third season episode “The Enterprise Incident.” It may also have been the case that the producers wanted to display the D7 model as much as possible as a courtesy to the model kit company Aluminum Model Toys which actually paid for it. In any event, the model’s whereabouts remain unknown.
The inconsistency of Romulans piloting Klingon ships was partly mended in the remastered version of “The Enterprise Incident” when an original Bird of Prey was added to the scene where three Romulan vessels surround the Enterprise. Romulan markings were also added to the underside of the D7s.
The remastered version of “Balance of Terror” includes a new shot showing the aft three quarters of the Bird of Prey.