John DeGennero was just 15 years old and playing at a park on the Sunday the Japanese attacked Pearl Harbor on December 7, 1941. After turning 17 in 1943, he joined the U.S. Marine Corps, determined to help win the war. Over the next two years, that teenager perfected a skill that would be crucial to winning the Battle of Iwo Jima. In this edition of "Veterans Chronicles," Mr. DeGennaro tells us about boot camp at Parris Island and then specializing in the science of sound ranging. From there he describes arriving at Iwo Jima and barely surviving his first night on the beach, watching the flag raising atop Mt. Suribachi, and the sounding ranging work he did to pinpoint and eliminate Japanese artillery positions on the island - and for which his unit was honored with a presidential citation. Finally, DeGennaro shares what the plan for his unit would have been if an invasion of Japan had been necessary - a plan he says that would likely have wiped out his entire division.