Following the Japanese attack on Pearl Harbor, Masters was promoted to the rank of captain in January 1942 and participated in the Russian convoy operations with British Home Fleet in the Norwegian Sea. Upon his promotion to major in September 1942, Masters was detached from "Tuscaloosa" and ordered to China, where he was appointed Commander of U.S. Naval Unit One, U.S. Naval Group China under Rear Admiral Milton E. Miles. Within this assignment, he was tasked with the training of Kuomintang guerrillas and was promoted to the rank of lieutenant colonel in January 1944.