[1] Fay B. Prickett, Robert B. McBride Jr., Horace L. McBride, William R. Woodward, Thomas Lyle Martin, Roland P. Shugg, Otto F. Lange, Louis E. Hibbs, Joseph M. Tully, Thomas D. Finley, William M. Hoge, Ludson D. Worsham, Dwight Johns, Calvin DeWitt Jr., Robert Neyland, Wilhelm D. Styer and James Joseph O'Hare, all of them destined to attain general officer rank, were among Reinhart's fellow graduates.

His first assignment after graduation was with the 5th Field Artillery Regiment, then stationed at Camp Bliss, Texas, where he served from September 1916 until June 1917, a few weeks after the American entry into World War I.

Following this, Reinhart, promoted to the temporary rank of major in July,[1] commanded the 1st Battalion, 17th Field Artillery Regiment (Battle of Soissons, Ypres-Lys, and Meuse-Argonne).

In Command of a battery and subsequently a battalion of the 17th Field Artillery, 2d Division, Major Reinhart gave proof of high qualities of leadership and military attainments, notably during the operations near Soissons in July 1918, when he skillfully maneuvered his battalion in front of the infantry under machine-gun fire from the enemy with but few casualties to his command.

After giving up his previous assignment with VI Corps, he served at Chaumont as a member of the historical section of the AEF's general staff.

He joined Lieutenant General George Patton's U.S. Third Army at the Sarre River, and fought with it on the Western Front across Germany and Austria.

His soldiers took the German cities of Saarlautern, Neunkirchen, Oberursel, Friedberg, Hattenback, Bebra, Rottenburg (Bavaria), Treffurt, Langensalza, Neumarkt, Regensburg, and Passau—as well as Schärding, Eferding, Linz, and Enns in Austria.

At the end of combat, Reinhart and the 65th Infantry Division were over 100 miles (160 kilometers) east of a north and south line through Berlin, Germany.

By now a major general, Reinhart arrived in Erlauf, a hamlet in Austria, where he met the Soviets and shook hands with his counterpart.