Miller decided for the career in the Marines and was commissioned second lieutenant on June 3, 1949. He was subsequently ordered to the Basic School at Quantico, Virginia, for officer training, which he completed in June 1950. Miller then joined the 3rd Battalion, 1st Marines and embarked for Korea as commander of the light machine gun platoon in "I" Company. He led his unit during the combat operations in Chosin Reservoir and was promoted to first lieutenant in June 1951.