Well, Naruto himself would probably be really excited. He'd be running around the military base, trying to make friends with everyone. His positive attitude might initially seem out of place in the strict military environment but could also start to change the atmosphere, making it more lively.
One possible storyline could be a Naruto - style ninja being part of a special unit in the German Army during a fictional alternate history. Maybe they use their ninja skills for stealth missions. For example, sneaking into enemy camps to gather intelligence, much like how Naruto and his friends would gather information in their own world.
Well, he might use his powerful jutsu like the Rasengan. He could also summon his toads to help him out in the battle against the army. Maybe he uses his shadow clone technique to confuse the enemy and then strike them when they're vulnerable.
Here are a few novels that describe the charge from the perspective of the German army: How I Fight the German Army, Soldier 004: Soldier, and Snow White Blood Red. These novels described in detail the charging scenes on the battlefield and their combat experiences from the perspective of the German soldiers.
Well, he might start by using his charisma. Naruto has always been good at making friends. He could reach out to old allies from his village, like Shikamaru and Choji. Also, he might convince some of the outcast ninja who have been mistreated in other villages to join him. His reputation as a hero who saved the world would surely attract a lot of people.
I'm not entirely sure specifically what a 'naruto is german fanfiction' is about without reading it. It could be a fan - created story where Naruto characters are placed in a German - inspired setting, or perhaps it involves Naruto characters interacting with German culture in some fictional way.
The unique feature is the language. German fanfiction can add a different flavor to the Naruto world with German expressions and idioms. For example, it might use German words to describe the jutsu, which gives a fresh take.
Perhaps it's for exploration. Naruto is always curious about the world outside. The robots can be sent to explore dangerous or uncharted areas where it might be too risky for humans to go. They can collect information and report back to Naruto.
Maybe Naruto has some knowledge from an unexpected source. For example, he could have met a wandering inventor who taught him the basics of robotics. With his determination and quick learning ability, he then starts building the robot army. He might also use his chakra in some unique way to power or control the robots.