Here is the basic gist. I am doing a family history and there was a captain of my grandfather who he cared about a lot. I have little to no information on him. Is there anyway of finding the unit and who this might have been?

I found a basic record for my grandfather on NARA though I am afraid this is all it has as far as designations.

GRADE: ALPHA DESIGNATION PVT# Private
GRADE: CODE 8 Private
BRANCH: ALPHA DESIGNATION BI# Branch Immaterial - Warrant Officers, USA
BRANCH: CODE 00 Branch Immaterial - Warrant Officers, USA

Any ideas where to start?

Thx in advance.