1. Draft Registration CardsMore than 24 million men (including immigrants who hadn't naturalized) registered for the draft in 1917 and 1918, although not all of them served. These are widely available on genealogy websites like Ancestry.com and FamilySearch.
2. State Adjutant General RostersMost states issued a roster of soldiers in World War I. Both Joe and Norbert are listed in The Official Roster of Ohio Soldiers, Sailors and Marines in the World War, 1917-18, on Ancestry.com as Ohio Soldiers in WWI, 1917-1918.

3. WWI Transport Service RecordsFold3 just published this collection of passenger lists of military transport ships. Norbert was listed with Supply Co. 336, leaving New York City Oct 27, 1918, and arriving in Liverpool Nov. 8. I had to scroll through the records to find a page with a date and ports.

He was on another ship Nov. 11, but I can't find a page noting where it took him. His last transport took him home: The USS Orizaba departed Brest, France, July 29, 1919, and arrived at Newport News, Va., Aug. 6.
4. Discharge Papers
Most discharged service members registered with their local courthouses on return to their communities. I can't find my WWI servicemen among the veteran discharges in FamilySearch's records for Hamilton County, Ohio, so here's the record for another man:

5. Veterans SurveysMany communities asked local veterans to complete surveys about their service in the World War. My cousin three times removed Louis E. Thoss filled out this one for the Kentucky Council of Defense (it's now part of the Kenton County Public Library's genealogy database).

The US Army Military History Institute also has a collection of WWI veterans questionnaires completed in the late 1970s, along with photos, letters, memoirs and other materials.
6. Military Headstone ApplicationWhen Joe died in 1941, his sister applied for a military headstone based on his WWI service. These are on National Archives microfilm, and digitized on Ancestry.com.

You'll find more ways to research your World War I ancestors in these articles:
- Top 10 websites for WWI research, in the July/August 2014 Family Tree Magazine digital issue (this includes those who fought for Great Britain and Canada)
- World War I online military records in the March/April
2017 Family Tree Magazine digital issue (focuses
on US involvement)
- Tracing World War I Women downloadable genealogy guide
Ancestry
| FamilySearch | Fold3 | Military records | World War One Genealogy