Franchini joined the United States Army in June 1917, even though he was not yet a citizen of the United States. He was placed in Battery F, 5th Division of the 19th Field Artillery Regiment, where he operated a 70mm gun. He spent ten months in training at a base near Leon Springs, Texas. Sent overseas, he landed in Brest, France, and conditioned there before being sent to the Vosges for combat. He spent eight months in combat, participating in the battles of Saint-Mihiel and Château-Thierry. As part of the occupation he was assigned to Koblenz and remained there until he was discharged on October 18, 1919.