Thomas A. Ryan entered the military service in Massachusetts. He served in the U.S. Army during World War I as a Corporal in the 101st Infantry Regiment, 26th Infantry "Yankee" Division. He died on July 23, 1918 and is now buried in Oise-Aisne American Cemetery, Seringes-et- Nesles, France. He was awarded the Distinguished Service Cross and it cites:
The Distinguished Service Cross is presented to Thomas A. Ryan, Private, U.S. Army, for extraordinary heroism in action while serving with Company D, 101st Infantry Regiment, 26th Division, A.E.F., near Epieds, France, July 23, 1918. Private Ryan, Sergeant Simeon L. Nickerson, andCorporal M. J. O'Connell volunteered to cross an open field in front of their company in order to ascertain the location of enemy machine-guns. While engaged in this courageous enterprise they were shot and killed. The heroic self-sacrifice of these three men saved the lives of many of their comrades, who would have been killed had the company attempted to make the advance as awhole. General Orders No. 116, War Department, 1918.