Who Mourns for Adonais? - S2-E2
Corrected entry: Spock says they've only managed to punch holes in the force field large enough to fire through. But when the Enterprise fires, the force field (in the shape of Apollo's hand) is no longer there at all. (00:44:30)
Correction: When the Enterprise fires on the temple, the force field IS visible. However, as they continue to fire and damage the power source, the force field starts to fade and flicker in and out, until it is gone.
Bishop73