 Holdridge was commissioned a Second Lieutenant in the U.S. Army in 1917, and assigned to the Quartermaster Corps of the Army's Reserve (II Corps) at Camp Gordon, Georgia.He was promoted to First Lieutenant by 1920, and made Captain two years later, at which time he was assigned to duty with Headquarters Army Trains, with the First United States Army in New York City.This move reunited him with his wife, who had remained behind in New York after his posting to Georgia, and led to the birth in 1924 of their only child, John H. Holdridge.