He was commissioned second lieutenant in Field Artillery Branch and attached to the 12th Field Artillery Regiment, 2nd Division. Wahl promptly reached the ranks of first lieutenant and captain and embarked for France in fall 1917. He participated in the battles of Saint-Mihiel, Blanc Mont Ridge and Argonne forest and received three Silver Star citations for bravery, Purple Heart for wounds and French Croix de guerre 1914–1918 with Guilt Star.