He embarked for France on February 4, 1918, as a member of the 119th Company of the First Replacement Battalion, U.S. Marine Corps, arriving in Brest on February 26. His company then entered training at Châtillon-sur-Cher, while Overton went to officers' training school at Gondremont, France, near Bezange-la-Grande. He graduated at the head of his class on May 31, 1918, and was sent on June 1 for observation with the Forty Second Regiment of French Chasseurs stationed in the Vosges Mountains. He was initiated as an honorary member of the French Chasseurs and remained with the regiment from June 1–13. When the Marines became engaged at Chateau-Thierry in early June, he asked to be transferred from his company which was still in training to the front line, and on June 16 he arrived at a marine camp in the middle of the Battle of Belleau Wood, which had begun June 1 and would continue until June 26. There, Overton was assigned second lieutenant in the 18th Company, 6th Regiment, U. S. Marines, a part of the 4th Brigade and 2nd Division. He served at Belleau Wood until July 9. On July 2 he was promoted to first lieutenant, but would not learn of that before his death. From July 9–16 he was stationed at Nanteuil-sur-Marne. On July 16, his regiment along with the 5th Regiment were moved to the French front near Soissons to join the Second Battle of the Marne. The division was then a part of Marshal Ferdinand Foch's allied offensive on the Soissons salient begun July 18, 1918, his division under French General Charles Mangin.