Clovis was assigned to the Mexico border for the following year. At the outbreak of the war, he was assigned to L-Company, 9th Infantry, 2nd Division at the rank of sergeant. He was one of the first Americans to go overseas with General Pershing after war was declared on Germany. On April 14, 1918 while in France’s Toul sector front line, Clovis and about 150 members of L-Company Americans and French Allied soldiers were stationed within a trench line holding the position. Without any warning, about 600 German soldiers swept over a barbed wire entanglement barrier and assaulted the outnumbered Allied troops in the trench. During the ensuing fighting, Clovis was wounded in his right arm by a hand grenade that had exploded near him. The German soldiers were able to overcome and capture the Allied troops. Subsequently the German soldiers were in the process of marching the captured Allied troops back towards German held lines, Clovis bolted from the marching ranks heading towards Allied trenches while being fired upon by his captors. Fortunately he was not hit by the gun fire. Upon reaching the safety of the Allied trench, Clovis was greeted by several German soldiers still occupying control of the trench. Clovis engaged in hand-to-hand combat with the German soldiers and he was eventually knocked unconscious by a rife-butt which smashed his shoulder.
Left for dead, the German soldiers retreated from their position. Clovis was later discovered by Allied troops and was transported back to a hospital where he remained there for two months recuperating from his injuries. After being released from the hospital, Clovis returned to duty and took part in the Chateau Thierry offensive of July 18, 1918 where he sustained a bullet wound in his right leg. This injury ended Clovis’ military career. Clovis returned to the United States from France and he received an Honorable Discharge from the United States Army at Fort Monroe, Virginia on 1st day of December, 1919.