I've looked at Memory Alpha, Weapons in Star Trek amongst others but there does seem to be an answer. Looking at the List of TOS episodes I'm suspecting Balance of Terror.
Does anyone know when the Enterprise first used her phasers that we can actually see?
-
No. I wanted chronological order. The first time we see her firing. Not logical time.– Athena WidgetDec 1, 2015 at 14:59
1 Answer
In episode 10 of the first season, "The Corbomite Maneuver", Enterprise destroys a warning buoy after it begins emitting dangerous levels of radiation.