One of The West Wing's best episodes (and my absolute favorite) covered that very subject (from season 1, "In Excelsis Deo"). A homeless man perished on the Mall, and the character Toby was called to identify him because his business card was found in the man's pocket. When Toby arrived, he didn't know the man, but he recognized the tattoo on the guy's arm as a Marine battallion tattoo. He'd come back from Korea and never really recovered or reassimilated into society.

It's an incredibly sad state when they train soldiers to go to battle but not take care of them on their return as part of the same process.