http://chroniclingamerica.loc.gov/lccn/ ... d-1/seq-1/
Shortly after the United State declared war on Germany, much to the chagrin of his mother, Vanderbilt enlisted in the U.S. Army in July 1917, at the age of 19. He was originally assigned to the headquarters of the ammunition train of the 27th Division of the New York National Guard, commanded by Major General John F. O'Ryan. His first posting was in Spartanburg, South Carolina where he was a wagoner driving mules.  As this assignment was not to his liking, Vanderbilt made a deal with General O'Ryan's orderly into changing his orders to go with the division overseas. In exchange, Vanderbilt became the orderly's assistant and helped with various chores. 
He went overseas with the division in May 1918 aboard the transport Great Northern. Upon arriving in Brest, France, he was assigned as an orderly to the commander of the U.S. Army stockade there. Vanderbilt disliked his commander, whom he referred to as "my torturer". By chance, he was able to get a temporary assignment as driver to General Douglas Haig, the commander of the British forces in France. He got the posting when he was in a group of soldiers who asked if anyone knew how to drive a Rolls Royce. Vanderbilt raised his hand since his family only used Rolls-Royces and he was familiar with the peculiarities of their operation. 
After his posting with General Haig, Vanderbilt was reassigned to the 27th Division's headquarters where he served as a driver delivering dispatches. While driving on one mission, Vanderbilt had a near fatal accident.
Vanderbilt's father was promoted to brigadier general in July 1918 and was reassigned as a brigade commander at Camp Lewis in Washington state. Both Vanderbilts returned to the United States in August 1918 after three months of service in France. The younger Vanderbilt was promoted to the rank of wagoner (equivalent to a corporal) on August 24th and served as a transportation instructor at American Lake, near Camp Lewis for the remainder of his military service.
Vanderbilt was honorably discharged from the Army on January 25, 1919.  Shortly thereafter, he was promoted to 2nd lieutenant of the Infantry branch in the Officers Reserve Corps. 
He went on to go through seven wives and wrote books and made films and squandered some money he probably didn't earn.