John Henry Callahan was born on December 5, 1923 in Missouri. He was the son of Zenephan Hickman Callahan and Bertha Elvada Fox Callahan. He was killed during the Exercise Tiger--one of the large-scale rehearsals for the D-Day invasion of Normandy. This took place in April 1944 in Slapton Sands, Devon in the UK. An Allied naval convoy involved in the exercise was attacked by German submarines, and coordination and communication problems resulted in friendly fire deaths. At least 749 American servicemen were killed. Because of the impending invasion of Normandy, the incident was highly classified and the full story did not come out until years later after the war. He died on April 28, 1944 and is now buried in Cambridge American Cemetery, Cambridge, United Kingdom.