It appears that the 151st Infantry Division was part of the Indiana National Guard and not Ohio.
He was then discharged from the National Guard into the American Expeditionary Forces.
Here is some information from Wikepedia about the AEF:
President Woodrow Wilson initially planned to give command of the AEF to General Frederick Funston, but after Funston's sudden death, Wilson appointed Major General John J. "Black Jack" Pershing in May 1917; Pershing remained in command for the entire war. Pershing insisted that American soldiers should be well-trained before going to Europe. As a result, few troops arrived before 1918. In addition, Pershing insisted that the American force would not be used merely to fill gaps in the French and British armies, and he resisted European efforts to have U.S. troops deployed as individual replacements in decimated Allied units. This attitude was not always well received by the Allied leaders who distrusted the potential of an army lacking experience in large-scale warfare.
By June 1917, 14,000 U.S. soldiers had already arrived in France, and by May 1918 over one million U.S. troops were stationed in France, half of them being on the front lines. Since the transport ships needed to bring American troops to Europe were scarce at the beginning, the army pressed into service cruise ships, seized German ships, and borrowed Allied ships to transport American soldiers from New York, New Jersey, and Newport News,Virginia. The mobilization effort taxed the American military to the limit and required new organizational strategies and command structures to transport great numbers of troops and supplies quickly and efficiently. The French harbors of Bordeaux, La Pallice, Saint Nazaire and Brest became the entry points into the French railway system which brought the US forces and their supplies to the front. American engineers in France built 82 new ship berths, nearly 1,000 miles of additional standard-gauge tracks and 100,000 miles of telephone and telegraph lines.
The first American troops, who were often called "Doughboys", first landed in Europe in June 1917. However the AEF did not participate at the front until late October 1917, when the 1st Division, a formation of experienced regular soldiers and the first division to arrive in France, entered the trenches near Nancy....
American Army and Marine Corps troops played a key role in helping stop the German thrust towards Paris, during the Second Battle of the Marne in June 1918 (at Château-Thierry and Belleau Wood). The first major and distinctly American offensive was the reduction of the Saint Mihiel salient in September 1918. During the Battle of Saint-Mihiel, beginning September 12, 1918, Pershing commanded the American First Army, comprising seven divisions and more than 500,000 men, in the largest offensive operation ever undertaken by United States armed forces to date. This successful offensive was followed by the Meuse-Argonne offensive, lasting from September 26 to November 11, 1918, during which General Pershing commanded more than one million American and French combatants. In these two military operations, Allied forces recovered more than two hundred square miles (520 km²) of French territory from the German army. By the time the Armistice had suspended all combat on November 11, 1918, the American Expeditionary Forces had evolved into a modern, combat-tested army.