In 1917, when the superintendent of schools offered a high school diploma to any student who joined the Army, 17-year-old Triplet accepted the offer. He joined the Missouri National Guard and served in France where he was gassed and shot in the shoulder. After being honorably discharged in 1919, he was admitted to West Point in 1920. He stayed in the Army after graduation, served in combat during World War II, and retired as a colonel in 1954.