After the catastrophe on the Somme in 1917, General Ludendorff was persuaded by a group of his junior staff officers to withdraw to a line running north-south behind the Canal du Nord between the Somme and the Scarpe River. By this move he saved his troops from a second Somme and shortened his line. More important, he gained the opportunity to prepare on virgin ground and far away from hostilities for defensive tactics which his bright young men, notably Colonel Fritz von Lossberg, had evolved for divisions after observing the French use for smaller units.
Old Stuff. Until 1917, each side attacked or defended linear fronts. In attack their tendency was to stretch and strain. On defense they tended to crack. Sent to the rear, Colonel Lossberg proceeded to construct a new kind of major fortification, based on zonal defense. He built what the Allies called the Hindenburg Line. It was not Hindenburg's and it was not a line. The Germans called it the Siegfried Stellung (Siegfried Position).
The tactical principle of the Siegfried Position was that of defense in depth; the idea being that an offensive force may crack a narrow wall but will be stopped or bounced back by a series of cushions and springs backing up each other. Colonel Lossberg's new type of front was some two miles deep, divided into forward zone, battle zone, rearward battle zone and two more rearward zones for mobile reserves.
Built of wire, wood, earth and some concrete, the Siegfried Position consisted of barbed wire entanglements, behind which came intrenchments and pillboxes connected with secondary intrenchments. Behind these were independent forts and strong points. From these, reserve troops, stationed far enough in the rear to be out of reach of enemy artillery, could be thrust out in any direction in counterattacks when the attacking enemy was exhausted by its advance. At this point the zonal defense system became an ideal means of launching a powerful offensive.
In April 1917, Colonel Lossberg was rewarded with the job of Ludendorff's Chief of Staff, and even though 18 months later his fortifications had fallen and his cause was lost, he had earned his brassard. When on September 29, 1918 the men of the U. S. II Corps went up against the final defenses of his Siegfried Position at Bellicourt, they had hell's own time. Between Bellicourt and Bony the St. Quentin Canal passed through a tunnel. In complete safety from shellfire the Germans massed reserve troops who lived in there on barges, ate in kitchens carved from the side of the tunnel and could mount to their hidden outside fighting positions through a maze of upward warrens. No sooner had the Americans seized one mouth of the tunnel than the Germans poured out of their surface positions and riddled them from the rear. The Americans finally cleared the area but not before the 107th Infantry had lost 337 men killed and 658 wounded, the heaviest loss on a single day for any U. S. regiment.