Just a couple of quick questions. I just finished this episode and was wondering.....
1) Did the Romulans really only have impulse power engines? If so how did they build an empire and keep it with such slow transportation?
The "Balance of Terror" was based in large part on the 1957 film "The Enemy Below", and it was important to the story that the Romulan ship mirror the characteristics of the German U-Boat when compared to the Enterprise. When submerged U-Boats were significantly slower as they had to run off of batteries rather than use their diesel engines as they would on the surface.
The following represents the best information on the speeds of the two ships portrayed in "The Enemy Below":
German U-Boat Speeds: 17.7 knots on the surface, 7.6 knots submerged
U.S. Destroyer Speed: 24 knots
So I'm sure that the Romulan ship could reach warp equivalent speeds (though not as fast as the Enterprise), but while cloaked she was forced to run at impulse power (similar to the limited speeds of battery power the U-boat was limited to while submerged).
They knew that without proof of them having attacked, the Enterprise wouldn't cross the boarder, so all they had to do was stay cloaked while they were on the Earth's side and could drop the cloak (and their speed limited) once they crossed back. But all of the action takes place in enemy territory so they had to remain cloaked during that time (other than to fire their weapon).
2) When they were firing phasers why did it look like photon torpedoes?
It should be noted that this was a very early episode in Star Trek history. In production order, it followed these episodes:
"The Cage"
"Where No Man Has Gone Before"
"The Corbomite Maneuver"
"Mudd's Women"
"The Enemy Within"
"The Man Trap"
"The Naked Time"
"Charlie X"
And in all of those previous episodes the Enterprise had only fired it's weapons once (to destroy the cube marker in "The Corbomite Maneuver"). So, at this point the Enterprise's weapons were called phasers, but they needed something that worked like depth charges from "The Enemy Below".
Later they would separate the abilities shown in "Balance of Terror" to the photon torpedoes, but those hadn't been invented in Trek by this point. As I recall, there wasn't a
Starfleet or
United Federation of Planets by this point in Trek either. This is very early Trek and much of the back story we take for granted today didn't exist yet.