Must possess a green card (be a resident alien) and usually there's a few more hoops to jump through after that. Then usually after serving 1 1/2 years active duty (IIRC), can become a U.S. Citizen.
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" And any man who may be asked in this century what he did to make his life worthwhile, I think can respond with a good deal of pride and satisfaction: 'I served in the United States Navy.'"- John F. Kennedy
"NUKE-ular. It's pronounced NUKE-ular."- Homer Simpson
"You should never underestimate the predictability of stupidity."- Bullet Tooth Tony
Run, jump, lift, puke, repeat.