Tunnell's neck injury in 1942 resulted in his being rejected in efforts to enlist in both the United States Army and Navy during World War II. In May 1943, Tunnell enlisted in the United States Coast Guard. From August 1943 to July 1944, he served on the USS "Etamin", a cargo ship that was manned by Coast Guard personnel and stationed in the South West Pacific Area. In April 1944, while unloading explosives and gasoline at Aitape in Papua New Guinea, the "Etamin" was struck by a torpedo dropped from a Japanese airplane; Tunnell saved a fellow crew member who was set afire in the blast, beat out the flames with his hands, sustained burns to his own hands, and carried the shipmate to safety. He was next stationed at San Francisco and Alameda from August 1944 to October 1945.