While much has been written about the Battle of the Bulge--Hitler's gigantic counteroffensive in the Ardennes Forest--the question of exactly how Germany was able to secretly mass its strategic reserves opposite the U.S. front remains as shrouded in mystery today as it was at the time. In December 1944, the snow-covered Ardennes was so quiet it was termed by Allied planners "the Ghost Front." The U.S. placed its greenest units among the wooded hills,...