Captain Klein was the pilot of a F-84E Thunderjet fighter with the 182nd Fighter-Bomber Squadron, 136th Fighter Bomber Wing. On July 25, 1951, while on a combat mission near Wonsan, North Korea, his aircraft received a direct hit by anti-aircraft fire, crashed and burst into flames. He was declared Missing in Action and was presumed dead on December 31, 1953. His remains were not recovered. His name is inscribed on the Courts of the Missing at the Honolulu Memorial.