Kidou Senshi Gundam: Rust Horizon

An Earth Federation Forces soldier named Nanao was in North America searching for the whereabouts of a new commander named Leo Barnaak who went missing before his arrival. Barnaak crash-landed in the Zeon sphere of influence, and Nanao and other platoon members risk their lives in pursuit of him, but find themselves in a desperate predicament as they meet with Zeon forces.

(Source: Shueisha, translated)