(I have looked through trekguide.com for this, but must not be doing it right...or maybe I am imagining things. In any event, hunting over 28.8 is wearing me down...)

Does anyone remember an episode in the original Star Trek that bears some resemblance to The 5th Element where there's an alien...and they fire photon torpedos at it...and the more they fire, the bigger/stronger it gets?

Am I imagining this? Anyone remember it and know the episode name? How. in the end, did Kirk and Company prevail???