He graduated from the United States Army War College in 1916, and served at Eagle Pass, Texas, during and after the Pancho Villa Expedition.

He led the brigade, part of the 7th Division, from training in Texas to embarkation at Camp Merritt, New Jersey, to combat on the Western Front, arriving in time for the final offensive before the armistice with Germany which caused hostilities to cease.

In Command of the 58th Infantry, 4th Division, from 6 August 1917 to 1 February 1918, General Wahl demonstrated leadership of a high order, untiring energy, and sound judgment.

He then served on the board that appraised civilian claims against the army for property lost and damaged during the war, reverting to the permanent rank of colonel.

His son, George Douglas Wahl, was a career army officer who achieved the rank of brigadier general.