If a legal permanent resident, he could join the
US Army (
source).
Legal Permanent Residents make up 2.8% of the active duty military.
About 8,000 Legal Permanent Residents enlist in the US Military each year, 4.3% of enlistments.
Since 1997, Non-Citizens rate of enlistments have remained stable.
Navy: 1995 - 4.7% 2003 - 5.8%
Army: 1995 - 4.3% 2003 - 4.2%
Marines: 1995 - 4.3% 2003 - 4.5%
Air Force: 1995 - 2.0% 2003 - 2.2%
Source
[Note: statistics source not cited]
In my 20 years' service, I've known German, Belize, Philippino, Thai, French Foreign Legion (he was not French, but spoke English with a French accent), a Brit or two, and Koreans who were in the US Army; though, the Koreans I knew were naturalized US citizens.
My
Ranger Buddy back in 1980 was German and had gone through the same Officer Candidate School class as I. Dunno how that worked because he said he was not a US citizen.
--Guy