Dorey led his regiment during the defensive actions of Aisne, Château-Thierry, Second Battle of the Marne, and in the Third Battle of the Aisne, Saint-Mihiel, Meuse-Argonne offensives. He distinguished himself in the combats north of Montfaucon on October 15, 1918, when during a 12 days' continuous fighting against stubborn resistance, his regiment suffered heavy casualties. Colonel Dorey, himself suffering from a painful wound, went forward from his post of command through a heavy enemy barrage to the front line, where he reorganized his forces and directed the attacking units for two days, until he was again severely wounded. His conspicuous bravery inspired his troops to the successful assault of a strongly fortified ravine and woods which were of vital importance and resulted in the capture of numerous prisoners and much material.