 Murphy had wanted to be a soldier all his youth and dreamed about combat. The death of his mother in May 1941 added even more impetus to his desire to achieve that goal. When he heard the news of Japan's 7 December attack on Pearl Harbor he tried to enlist in the Marines, the Navy and the Army, but was turned down for being underweight and underage. He added weight with a change in diet, and gave the Army an affidavit from his sister Corinne that falsified his birth date by a year. Murphy enlisted on 30 June 1942 in Dallas. During his physical examination his height was recorded as 5 feet 5.5 inches (1.66 m) and his weight as 112 pounds (50.8 kg). Assigned to the infantry, during basic training at Camp Wolters, Texas, Murphy earned the Marksman Badge with Rifle Clasp and the Expert Badge with Bayonet Clasp. While participating in a close-order drill during that hot Texas summer, he passed out. His company commander thought his build was too slight for service in the infantry, and tried to have him transferred to a cook and bakers' school, but Murphy insisted on becoming a combat soldier. He completed the 13-week basic training course and in October was given leave to visit his family, after which he was sent to Fort George G. Meade in Maryland for advanced infantry training until January 1943.
