This man served in the 42nd Rainbow Division during WWI. How do I add a category to denote his service?
I'd start here:
The project has a number of recommendations as it relates to how to categorize and how to recognize veterans from WW I.
At the very least, you should be able to put him in: [[Category:United States Army, World War I]]
And I didn't see the 42ID as a category at this time, so if you wanted a category to be created, you'd just need to request it.
I stand corrected - apparently they were part of the Expeditionary forces:
[[Category: 42nd Infantry Division, United States Army, World War I]]