Hello there! As your question is related to looking for identification/information regarding military personnel, our Guide on Military Identification may be of use to you. It provides a number of different resources, including how to request service records from a number of national agencies around the world, as well as graphical aids to assist in deciphering rank, unit, and other forms of badges or insignia. While the users here may still be able to lend you more assistance, hopefully this will provide a good place to start!

Your great grandfather boasted extensive service in World War I. The United States was involved for about nineteen months, but frontline offensive operations only became commonplace from the spring of 1918 onwards as the number of American divisions arriving in France increased rapidly. As there was not separate medals denoting individual theaters of operations (the majority of American troops fought in France, but there were small numbers in Italy and Russia), the full-sized World War I Victory Medal was authorized to be worn with clasps denoting participation in major operations.

The "Defensive Sector" clasp was authorized for service in operations which did not already have their own clasps.

3/16" bronze stars corresponding to each operation given a clasp could be worn on the medal ribbon. The other two ribbons are the Army of Occupation of Germany Ribbon and the Certificate of Merit Ribbon; the latter is especially prized among historians and collectors, as it was rarely awarded, and after it became obsolete was often turned in and exchanged for the Distinguished Service Medal or the Distinguished Service Cross.