At the top of this military roster, it says, "Roster of Supply Company, 19th Infantry. At Midnight January 31, 1919." For the Military Unit field, would I put "19th Infantry", or "Supply Company, 19th Infantry"?
You will put the latter. From the Field Help (purple question mark in the Military Unit field:
Type the entire name of the military unit as it was recorded, including the company, regiment, battalion, and so on if they were included. Do not correct misspellings or expand abbreviations.
Got it. Thank you!