History books may claim WWII began in 1939, but Germany's preparations for the war began years earlier. Long before the first shot was fired, Hitler began a slow build up in the East. Under the guise of waterway projects, dams and drawbridges, Germany began work on what would become their most technologically advanced front. By 1938, the Germans had eighty kilometers of tobruks, bunkers, tunnels and factories built into the Festungfront Oder-Warth-Bogen. Though Hitler would brag about the Siegfried Line and the Atlantic Wall, he'd keep the Eastern front to himself. As Germans scoffed over unprotected Eastern borders, flamethrowers and guns were trained to the east, ready for attack. How and why did Hitler keep this front a secret? And how did he build it right under the Allies' noses? How did a line built to house 25,000 soldiers fall to the Russians in just three days? And what can Germany's forgotten front tell us about Germany's hidden military might?