A Star Trek film, Planet of the Titans, would have gone back to the dawn of time

Just imagine it. Captain James T. Kirk [William Shatner], Spock [Leonard Nimoy], and Dr. Leonard "Bones' Mcoy [DeForest Kelley], along with the rest of the crew of Star Trek: The Original Series heading back to the dawn of history to help out the first humans. Yes, this almost happened after Star Trek's syndicated ratings went through the roof.

Of course Paramount wanted to see if they could make more money off of the series so the team put their collective heads together and tried to come up with a concept that would work. They considered another animated show, a television movie, and even another live-action series, but no one could quite pin down what should be done. Eventually, it was decided that a theatrical film would work and so the concepts began. [via Den of Geek]

Star Trek: Planet of the Titans would have taken The Original Series crew way back in history to a point in time where mankind hadn't yet discovered fire. That would have been something that the Enterprise crew would have proffered. That would have been difficult to explain, considering the Prime Directive forbids the interference of natural development of planets and aliens. Obviously, though, there would have been a moment during the film that fire was required, and Captain Kirk would have had no other choice but to provide it.

Alas, the movie didn't make it past development, though, concept art by Ralph McQuarrie was commissioned, which included an Enterprise refit, and though it wasn't used in the that movie, it was used in Star Trek III: The Search for Spock and some episodes of Star Trek: The Next Generation. You can see the images at ForgottenTrek.com like this one. This definitely sounds like a different type of Trek. And who knows? This concepte could still come to fruition in a Star Trek series or later movie.