

Making it look like a Federation ship may make the other guy hesitate long enough to get off that vital first shot. A swift reacting enemy would have an advantage in combat. It is tactically vulnerable at these moments. It also takes time materialising and dematerialising during cloaking. The ship is testing a new ship mounted cloaking device which uses enormous amounts of fuel to operate. Which then begs the question why? Let's look at the episode for a moment. And only this one time, judging by later series ship depictions. That explains why it isn't the typical Romulan green hulled designs we see earlier in 'Enterprise' and later in TNG and beyond - its copying their main enemy's technology. The Romulan ship was based on stolen Federation ship designs. Well, according to this deleted scene, that mystery is finally solved. Many have previously commented on the resemblence of the TOS Bird Of Prey to Federation vessels.


One of particular interest is this one on the episode 'Balance Of Terror'. With, among other things, deleted scenes from the TOS episodes.
