Thirty years ago, a young Frenchman walking in Normandy came across an American soldier's rusted dog tag among the rocks at Nacqueville, west of the port of Cherbourg. The name read: "Addison W. Arthurs." Etienne Desquesnes, now 46, wanted to return it to the owner or his family. But who was Addison Arthurs? Mr. Desquesnes wrote to the U.S. embassy in Paris but never got an answer. He finally has one now, and just in time for Veterans Day, thanks to some Internet sleuthing by his friend, Bertrand Goucovitch, 49, an amateur D-Day historian, and the Pittsburgh Post-Gazette. After a...