I would start with trying to get some military records on him. As you know his WWII regiment, I'd start with those. These might list his earlier service in WWI & list the Regiment/Division.
~ There is information re: obtaining Military records on the National Archives site: http://www.nara.gov/research/ordering/milordr.html#nprc
Later Military service records are in the Nat. Personnel Records Center in St. Louis, and many of the WWI records were destroyed in a fire. There are links at the Archive site above that explain more.
~This web site: http://www.geocities.com/lks_friday/COLUMN-013.htm
Has a great article on WWI Service Cards and although written with Texas records in mind, there is a link for where to write for other states.
~ You might also want to see if there is a web site for his WWII Regiment - 210th (I'm not sure what A.A. stands for) - (The Destroyer Escort my Dad served on has its own site) -
~ Also check out the US Army Military History Institute's web site: http://carlisle-www.army.mil/usamhi/
They have a wealth of information and you can send questions by e-mail or can phone them.
Hope this helps. Let me know how you make out...I really would like to know what you find out.
Take Care, Eileen Campos