Given the challenge of escorting colossal machines across hostile lands, a small group of unexpected heroes manage to have a lot of fun, get into a lot of trouble, and save the world.

What time frame? What genre (feels sci-fi...but better to know) ? Why care about band of main protagonists (flaws)? What is clearly at stake? Please write this movie, don't loose the part of escorting the machinery that was the draw for me to even review this logline. I like that concept. I imagined mammoth mechanical beasts having to make an epic journey through a desert wastelands filled with bandits looking to capture the machines for wealth. I would watch this film. Thanks!

In preparation for imminent war against the Junkarthe siblings' militia, a small band of reckless heroes must escort colossal machines to orchestrate the ultimate defensive.

Thank you for the very helpful comments! I'm going to think them over a little more and report back.

Adding on to what's been said above, I'd like to see more of an antagonistic force. The wastelands are pretty antagonistic, but can you state it in a way that sounds more imposing? Is there a ticking clock? What happens if they fail?

no wait.. In preparation for imminent war against [adverb] X a small band of reckless heroes must escort colossal machines across hostile lands to orchestrate the ultimate defensive.?

... Yes, only to encounter the antagonist. But if you give away 'to much' in the logline the audience is not going to see the movie.
"In preparation for imminent war against [adverb] X a small band of reckless heroes must escort colossal machines to orchestrate the ultimate defensive."

I like it. It isn't quite there as the previous comments have mentioned, but I think it is great at getting across a fun and stylistic tone that makes it sound like an enjoyable concept.

Not bad. But a little more is needed. ....only to encounter (something). It feels like the bones of a story and not an entire story.

In preparation for imminent war, a small band of reckless heroes must escort colossal machines to orchestrate the ultimate defensive.