Gentlemen,
Maybe many units were "nationalized" on March 5, 1941? The Unit Randy speaks of, the 33rd Infantry, was activated on that day, but as he said they eventually ended up in the Pacific. Maybe he transferred to another unit between the time the unit was activated and the time they headed to the Pacific? At this point I do not see another Illinois National Guard unit being federalized. Here's a link to a book that lists all of the National Guard units activated during WW II:
http://ufdc.ufl.edu/UF00047651/00001/62j
Gary
p.s. Dennis, I located your father's enlistment record dated 5 Mar 1941 and for branch it lists the following:
Medical Department - For Enlisted Men of the Medical Department (includes Enlisted Men of the Medical Department on Duty with the Dental Corps)
Proud Grandson of Randall Gates
Mechanic, A and H&S Companies, 292nd Engineer Combat Battalion, 1149th Engineer Combat Group