Following the United States' entry into World War I in April 1917, Dorey was appointed aide-de-camp to his former superior and now commanding general of Camp Funston, Kansas, Major General Leonard Wood. Wood was responsible for the training of nearly 40,000 men and appointed Dorey as commanding officer of the Citizens' Military Training Camp, the first businessmen's training camp at Plattsburgh, New York. He later received temporary promotion to colonel and embarked for France in early 1918. Dorey assumed duty as commanding officer of the 4th Infantry Regiment and led it for the duration of the war.[3]
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 fighting north of Montfaucon on October 15, 1918, when during 12 days of continuous fighting against stubborn resistance, his regiment suffered heavy casualties. Colonel Dorey, himself suffering from a painful wound, went forward from his command post 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.[2]
Following the war, Dorey graduated from the Army War College in 1921, reached the rank of brigadier general in December 1922 and commanded the 14th Infantry Brigade from January 30, 1923, to February 12, 1925, and the 18th Infantry Brigade from December 1927 to October 16, 1928. He was promoted to major general in November 1933 and assumed command of the 2nd Infantry Division the following month.[3][4]
Dorey was ordered to Hawaii in June 1934 and commanded the Hawaiian Division until December 1935, with additional duty as temporary commanding general of the Hawaiian Department until March 1935. General Dorey retired from active duty on February 29, 1936, and settled at Fort Sam Houston, Texas.[3][4]