Some common themes could be Naruto characters adapting to the US Army's discipline. For example, Naruto's determination in the Naruto world might translate to his eagerness to succeed in military training. Another theme could be teamwork. In Naruto, teamwork among the ninja squads is crucial, and in a US Army - Naruto fanfic, it could be about how Naruto and his friends from the series work together with US Army soldiers on missions. Also, there might be a theme of cultural clash, as the ninja culture from Naruto meets the military culture of the US Army.
Naruto could be a special forces type of soldier. His high energy and determination would make him excellent in combat situations. Sasuke could be in an intelligence role, using his Sharingan to gather information. Sakura, with her medical skills, would be a great field medic. They could all fit in as part of a special unit within the US Army.
Naruto could be a special ops agent. His agility and quick - thinking from his ninja training would make him perfect for dangerous and covert missions.
One way this could work is if Naruto's world somehow merged with ours and he was drawn to the US Army's values of courage and teamwork. His ninja skills like speed and stealth could be very useful in military operations. He might also bring his strong sense of justice, which could influence the way the army operates in terms of protecting the innocent.
Naruto's superhuman strength and speed could make him an excellent front - line soldier. His ability to jump great heights and distances would be useful in urban combat or when crossing difficult terrains.
One possible storyline could be Naruto being recruited into a special unit of the US Army. He could use his ninja skills like shadow clones for scouting or his Rasengan as a powerful weapon in combat situations against fictional threats.
I'm not entirely sure as I haven't read that specific 'fanfic'. It could potentially be a story where Naruto has some sort of encounter with an army and there are killings involved in a fictional scenario created by the fanfic writer.
It could be an organization similar to the Akatsuki, but with a different goal. Instead of collecting tailed beasts, they are focused on conquering villages. Their army would be made up of powerful and diverse fighters, and Naruto would have to face their leader, who has some sort of special power or ability that makes them a formidable foe.
One main theme is leadership. Naruto has to step up and lead the newly - found army. He has to make decisions and inspire the members. Another theme is unity. The army, which may consist of different types of people or beings, has to come together and work as one. For example, if there are members from different villages in the army, they need to put aside their old rivalries.
Well, I'm not sure of the exact name, but there's a 'naruto finds an army' fanfic where Naruto finds an army of ancient warriors. These warriors were sealed away long ago and Naruto accidentally releases them. At first, they are hostile, but Naruto manages to convince them to help him fight against a common enemy. The fanfic is really interesting as it combines elements of Naruto's world with ancient legends.