The Mission: Impossible franchise has always been about Tom Cruise doing incredible stunts. With each successive entry the actor has looked for new ways to put his body on the line. At this point what Tom Cruise is going to do in the Mission: Impossible movies is perhaps more interesting than what plot Ethan Hunt is going to find himself involved in. And it turns out that the franchise's focus on action literally traces back to the very first film in the series, as the movie's climactic train sequence was conceived of before there was a story.
It's the 25th anniversary of the original Mission: Impossible and a brand new Blu-ray release celebrating that includes a sit down interview with Tom Cruise conducted by current Mission: Impossible writer/director Christopher McQuarrie. In the interview Cruise reveals that director Brian de Palma had the idea to do a sequence on a train before they had put together any sort of plot for the film. They even started mapping out how such a sequence would be filmed before figuring out how any of it would fit in the actual movie. According to Cruise...
I remember the train. He was like ‘I wanna do a train.’ I was like ‘That’s fantastic.’ And so how do we do it? How are we going to shoot this thing? We would sit there with train cars, and we didn’t have the story. Surprise, there was no story. But we were like this is a cool idea.
The first Mission: Impossible movie ends with a sequence on board a high speed train moving through the Chunnel. Tom Cruise's character finds himself fighting the bad guys on top of the train and even jumping between the train and a helicopter. It's an impressive sequence, so it's no wonder everybody really wanted to do it, and they certainly found a way to make it fit in the movie. One can imagine the entire story was possibly put together in such a way as to justify the sequence.
The train sequence in the first Mission: Impossible is somewhat unique in the franchise as it is not an entirely practical shoot. The scenes were mostly shot on a sound stage and do include digital effects from ILM. However, some practical filming on a moving train was done, and Tom Cruise does all the work himself as one has come to expect from him.
One has to wonder if the fact that the train sequence in the first movie isn't entirely practical may have led to the fact that the new Mission: Impossible movie will also include sequences of fighting on top of a train. Perhaps Tom Cruise felt slighted not being able to do everything on location the first time around.