Editing Bird-of-Prey (section)

===Inconsistencies===
The question of whether the Bird-of-Prey had warp capability is one that has divided fandom. The Star Trek Encyclopedia claims that the vessel only had impulse engines. Scotty's precise line from "Balance of Terror", however, actually says "their power is simple impulse", possibly referring to their power generators, not necessarily their propulsion system. Kirk did say "We can outrun them", which seems to imply that the "impulse" Scotty was referring to was in fact the propulsion system. It seems reasonable to assume that Scotty meant that they did not use the same type of power system (matter/antimatter reaction) used by the Federation, and that the Romulan ship was capable of propelling itself faster than light with the (rather large) engines it mounted, inducing a warp effect by a simpler, brute-force method. 

Whatever was said, the Romulans must have some form of faster-than-light drive or they could not have engaged the Earth in an interstellar war in the 22nd century. Perhaps the fuller meaning of Scotty's line is that the Romulans did not have FTL drive of the same type or capabilities as the current type of warp drive used by the Enterprise, or that the early cloak required so much power that it couldn't be used at the same time as warp engines. 

Visual evidence (such as the presence of warp nacelle-like objects on the model) also suggest that the ship had faster-than-light capability, as does the fact that the Enterprise was traveling at warp speeds for much of the engagement with the Romulans. 

Some fans speculate that the powerful plasma weapon in conjunction with the equally powerful cloaking device proved too debilitating for both the ship's power and the Bird-of-Prey's propulsion system (which may very well have been warp drive), leading the Romulan Star Empire to negotiate with the Klingons for an exchange of the cloaking technology for their ships and schematics. 

Other evidence proves that theory wrong. In season four of Star Trek: Enterprise, the three-part Romulan story arc features a refitted warbird that was warp-capable. That would make it seem highly unlikely that the Bird-of-Prey wouldn't have warp drive when it was built more than a hundred years later. 

The bottom line is that no matter what Scotty's "their power is simple impulse" line was meant to mean, the fact of the matter is that the ship had to be traveling faster than light in order to travel the distance they traveled. If Scotty's line was indeed referring to the ship's speed, then really all that we need to do is realize that this was either just an error or the speed the Romulan Bird-of-Prey chose to maintain or could only maintain. The latter of the two seems most likely since it was clearly established in "Balance of Terror" that the Bird-of-Prey's fuel was "low" and "all but gone" with the fuel reserve completely "gone." 

The frequent mentions of fuel status also tie in nicely with dialog from "The Doomsday Machine" (among other episodes) that suggests that impulse power (ie, a fusion reaction) can propel a starship at faster than light speeds, but at a severe loss of "fuel efficiency", and possibly a lower top speed. 
 

With these combined abilities, the Bird-of-Prey was able to strike its enemies at will, practically undetected and unchallenged. (TOS: "Balance of Terror", "The Deadly Years")