As far I know "USAI" has always meant "United States Army Intelligence". My husband was a trained as a radarman and was on a CVE during the war. When the war ended a service man was discharged according to a point system. Married men with dependants were awarded the most points, then married men w/o dependants, then single men. My husband said it seemed to him they wanted to keep the single men in the longest to talk them into "shipping over" (Re-enlisting). He was kept on base doing odd jobs, nothing to do with radar work, and trucked to others bases for what he calls "busy work". Could be your relative was assigned "busy work" that involved an Army unit.