13 Times Star Trek Broke Its Own Prime Directive
12. For The World Is Hollow And I Have Touched The Sky - Original Star Trek
Captain James T. Kirk is known for many things, not the least of which being his tendency to break the prime directive like it's going out of style. But at least with this one, his actions were pretty justified.
In the episode For The World Is Hollow And I Have Touched The Sky, a Generation class ship called the Yonada that's disguised as an asteroid, and also just happens to be headed on a collision course with a populated planet. After some shenanigans involving McCoy falling in love with a woman he met that same day, and finding some ancient text for the aliens living aboard the Yonada, Kirk manages to get the ship back on its correct course.
This is a more light breaking of the prime directive since, technically speaking you could argue that Kirk finding those texts if interfering with the alien society of the Yonada. But on the other hand, if he HADN'T found it, the ship would have collided with the planet and killed untold amounts of people. So I think the federation will let bygones be bygones this time.