Captain Klein was the pilot of a F-84E Thunderjet fighter with the 182nd Fighter-Bomber Squadron, 136th Fighter Bomber Wing. On 25 July 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 31 December 1953. His remains were not recovered. His name is inscribed on the Courts of the Missing at the Honolulu Memorial.

Klein was awarded the Air Medal with Oak Leaf Cluster, the Purple Heart, the Korean Service Medal, the United Nations Service Medal, the National Defense Service Medal, the Korean Presidential Unit Citation and the Republic of Korea War Service Medal.