In 1901, he was commissioned a
second lieutenant in the 12th Infantry Regiment of the
New York National Guard and he remained a member of the National Guard for 33 years. He was promoted to first lieutenant in December 1902 and served as an aide-de-camp to the Governor of New York from September 1903 to December 1904. He was promoted to captain in June 1907 and served as an aide to the division commander from October 1908 until being promoted to lieutenant colonel and inspector general in June 1912. Along with most of the National Guard, Vanderbilt was mobilized on 30 June 1916 and served on the Mexican border in the
Pancho Villa Expedition, during the
Mexican Border War. When the United States
declared war on Germany and entered
World War I in April 1917. Vanderbilt was promoted to colonel on 20 July and placed in command of the 22nd Engineer Regiment of the New York National Guard. The regiment was re-designated as the 102nd Engineer Regiment on 1 October 1917 and became part of the newly organized
27th Division, which was composed of activated units of the
New York National Guard. The 27th Division departed New York for
Camp Wadsworth in
Spartanburg, South Carolina in September 1917 and was shipped overseas to France in May and June 1918. In July 1918, shortly after his arrival in France, Vanderbilt was promoted to
brigadier general. Shortly thereafter, he returned from France to the United States and was assigned to
Camp Lewis in
Washington state, where he arrived on August 20 and assumed command of the 25th Brigade, which was part of the 13th Division of which he was acting commander from August 20 to September 11, 1918. As most new recruits and draftees were being sent to France to replace casualties, the 13th Division never reached full strength until November 1, 1918, which was just nine days before the
armistice with Germany which ended hostilities, and, therefore, it was never sent overseas. General Vanderbilt was reassigned on December 20, 1918, and resigned his commission in the US Army on January 3, 1919.
Military awards For his services during the war, General Vanderbilt was decorated with the
Army Distinguished Service Medal by the War Department and the New York State
Conspicuous Service Cross (recipient #190). He was also made a commander of the
Order of the Crown of Belgium and was awarded that country's
Croix de Guerre. The government of France invested him as a Commander of the
Legion of Honor. He was also a recipient of the
Mexican Border Service Medal and
World War I Victory Medal. His citation for the Army Distinguished Service Medal, awarded in 1919, is as follows: ''The President of the United States of America, authorized by Act of Congress, July 9, 1918, takes pleasure in presenting the Army Distinguished Service Medal to Brigadier General Cornelius Vanderbilt, United States Army, for exceptionally meritorious and distinguished services to the Government of the United States, in a duty of great responsibility during World War I. As Commanding Officer, 102d Engineers, and as Engineer Officer of the 27th Division, General Vanderbilt's marked qualities of leadership and thorough training and instruction developed a high state of military efficiency in his command, as demonstrated throughout its entire service.''
Post war service After the war, Vanderbilt remained active in the New York National Guard and Organized Reserve. He commanded the
77th Infantry Division of the
Organized Reserve Corps from May 1922 to January 1929, and from November 1929 until relinquishing command in January 1935. ==Postwar life==