Hi Margie,

This site has helpful info on WW1 and naturalization rules, and tips on where to research those who naturalized while serving in the U.S. military:

United States World War I Naturalization and Citizenship
https://www.familysearch.org/wiki/en/United_States_World_War_I_Naturalization_and_Citizenship

Also, men who signed up for the military in WW1 prior to the draft cards, would not have filled out a draft card.  Unlike WW11, not all men were drafted.  So, if you see a WW1 draft card for someone, that does not mean that they ever served.

Regards,

Sherri Bobish