He will likely be assigned to a military intelligence unit depending on his exact qualifications. He can expect to serve anywhere, from front line Ranger and Special Forces units as the unit translator to liason work to translating documents in the rear. Since the jihadis seem to shun radio and telephone transmissions, he will likely be doing face to face interrogations and translations.
One guy I knew in the Army was a Russian translator who's job it was to escort convoys of building materials from Helsinki to Moscow for the new embassy.
His weapon and his unit will be his bodyguard. And he will work as long as the unit he is assigned to works. He may have to fight, but I hope he never has to.
As far as green to gold, he can work towards Officer Candidate School (OCS). He needs to have a good record and get the recommendation of his superiors to get accepted.
I wish your friend luck.
Personal experience. I was a Russian linguist back in the day.