Before landing in France on D-Day, June 6, 1944, the Allies executed an elaborate deception plan designed to prevent the Germans from concentrating forces in Normandy. The lesser-known first part, Fortitude North, suggested a threat to Norway. The more famous Fortitude South indicated that the invasion would occur at the Pas de Calais rather than Normandy, largely by creating a fictitious army group under Gen. George S. Patton. While historians have...