Is your inquiry specific to those branches alone or does it include our states’ National Guard services? Either way...I don’t know but I would like to know.
He is looking to immigrate to the US and find a “full time” career in the US military. While I know there are skeleton staffs in the NatGuard units who are full time, those jobs are usually highly sought after by long timers.
He wants to go active duty, do his tours, gain citizenship, and become an American before he settles down.
If your friend has a much needed skill set, such as strong language skills in other languages, scientific background, or a medical doctor then there are ways to sneak past the “U.S military will not help in obtaining a greencard”.
The easiest way to find out is to contact a recruiter.
I know somebody that was a soldier in the Swedish Military, then became a U.S Marine, then went back to the Swedish Military.
Yes it happens.
Had a LT worked for me who was from New Zealand. Enlisted in the Corps, did his term, got out, got his college degree then came back in as an officer.