Sorry, I'm not a military historian. You could contact the people at www.cantigny.org/museums/
They are the "Big Red One" First Army history people. They may have information to help.
If all you are doing is cataloging people look to see if you can use Address Book type software. If you have any programming background using MS-ACCESS Address Book as a base you could add a few additional fields to store unit information, citations, battle names, etc.
Also, you could use business software for department structure, or social networking software to maintain relationships between people in units.