Robert McCormick received a special temporary commission as a Colonel in the Illinois National Guard August 23, 1915 allowing him to travel in Russia and report on World War I for the Chicago Tribune. This commission expired when he returned to Chicago but on June 21, 1916, he received a new commission, this time as a Major in the First Calvary. He served with Brigadier General John J. Pershing when the First Cavalry shipped out to Brownsville, Texas to support the Mexican Border Campaign. Robert supplied the troops through significant personal contributions of weapons, ammunition and transport vehicles.
In 1917, Robert mustered into Federal service, becoming part of the First Infantry Division, and reported to Pershing’s headquarters in France. He served with the 5th Field Artillery of the American Expeditionary Forces and from April 20th to May 28, 1918, fought during the Battle of Cantigny. This battle affected him so strongly that after the war he renamed his Wheaton farm in its honor. He received the Distinguished Service Medal for his contributions to “the successful operations of the artillery of the American Expeditionary Forces.”
He was promoted to Lt. Colonel in June, 1918 and to Colonel of the 61st Field Artillery on September 5th. Honorably discharged on December 31st, 1918 he was known as “The Colonel” for the rest of his life.