Do you have WWI enlistment information?

It is possible he registered for the draft. The First World War selective service (draft) records (including the 4th registration) are in the custody of the National Archives at Atlanta, 5780 Jonesboro Road, Morrow, GA 30260. The email address is altanta.archives@nara.gov.

If you can identify the US Army World War I regiment in which your uncle served there may be information in the collection "Records of Divisions, 1917-1920" catalog # 301641. Stored at US National Archives at College Park MD are over 5,000 boxes arranged by the standard military decimal code for each Division and they contain a wide variety of information that is NOT indexed. The paper finding aid lists many of the boxes, while the box list in the catalog is out-of-date. This is challenging research, but if you are interested in ordinary, everyday soldiers it contains some fascinating documents, for example letters written by parents in 1919 asking the commanding office if their son can be discharged to come home and help on the farm, also soldiers asking if they can be discharged in Europe to visit their parents at their home in Italy. There are different documents in different divisions, more documents for the 3rd division which was in Europe several years and fewer boxes of documents for a division that was discharged early in 1919. To read a few examples, search [sites google "family information from us army" us archives].