In earlier drafts of the story, instead of Han joining the Empire, he actually joined a diverse rebel army fighting against Imperial forces.
During his time as a foot soldier in the WWI-esque battle, he would find himself paired up with Chewbacca, and the massive Wookie would save him from a looming Imperial walker.
In a recent interview with Screen Rant, Industrial Light and Magic senior art director Aaron McBride addressed the relationship between Han and Chewie in Solo: A Star Wars Story and explained how it evolved over time.
His time as a cocky hotshot pilot eventually would get him into trouble (with comparisons made to Top Gun), and he would be sent to the fight the Empire on the battlefield in the ground war on Mimban.