Last year, I used the Texas Tech University web site cited earlier to learn about my unit activities in Viet Nam in 1970. After a short while, I was finally able to figure out how to do searchs and download the Command Chronologies for the 1st Marine Divison and my regiment (5th) and battalion (2/5). The Command Chronologies are a monthly summary of events and also include the daily Staff Journal. I was surprised the regiment staff journal on a number of occasions had more information about an incident than the battalion staff journal.
I assume the U.S. Army had similar monthly reports, but I don't know what the precise term is for them. I would suggest you start with your division, then work down to battalion/company level.
Good luck in your search for documentation.