Why the Hindenburg Line Failed

The Hindenburg Line, as it was known by the Allied  armies, was the strongest defensive system built during the First World War. Its reputation for impregnability was matched only by its ambitious design. Jagging across most of the Western Front in Belgium and northern France, nothing like it had ever been seen before. Requiring an enormous amount of labor and material, its extensive fortifications included deep zig-zagging trench lines fortified with reinforced concrete shelters, heavily armed strongpoints, and wide belts of barbed wire combined to form an intimidating barrier for any attacking army and to maximize the firepower of war's two greatest killers—artillery and machine guns. 

This nearly complete section east of Lens show the main of the Hindenburg Line: a position commanding the countryside,  hidden concrete bunkers (see photo below), two thick belts of barbed wire, protecting the main position,  and thinner belts for the advance and communications trenches.

The fortifications also skillfully integrated natural topographic features such as ravines, villages, and waterways to afford every possible advantage to the defending troops and make any Allied advance as difficult and dangerous as possible. Perhaps its most ingenious use of terrain was creating the world's longest anti-tank ditch from the St. Quentin Canal. To drive the Germans from French soil, the Allies knew they had to overcome these obstacles—and it was a deadly task requiring new weapons and tactics. 

The origin of the Hindenburg, or Siegfried, fortifications lay in two major German defeats of 1916. The first was the Fifth Army's offensive at Verdun, which failed to weaken the French Army through attrition. The battle turned into a bloody six-month (February to July) stalemate that left both the German and French armies exhausted. 

The second was the Anglo-French offensive on the Somme that began in July and relentlessly wore down the German First and Second Armies and slowly pushed the front line back to create a salient. These two lengthy and intense battles inflicted more than 700,000 casualties on the German Army and consumed vast quantities of weapons and munitions, leaving it in a much weaker state relative to the British and French Armies.

The Hindenburg Line symbolized the quandary in which Germany found itself on the Western Front in the second half of the war. On one hand, it could not afford any more costly battles like Verdun or the Somme and it needed the fortifications to even the military balance. On the other hand, once the United States entered the war, Germany could not win the war by merely occupying fortifications and keeping its army on the defensive. 

The original purpose of the Siegfried positions was to conserve the German strength while inflicting unacceptable casualties upon the French and British Armies, possibly forcing the Allies to negotiate a favorable peace treaty while Germany still occupied Belgium and northern France. To that end, OHL's best option may have been to continue strengthening the fortifications and not abandon them for a desperate offensive that was uncertain of delivering a knockout blow to the Allies. But Germany did not have the resources to build an impregnable defensive front. After the initial round of construction that built the Siegfried and Wotan positions, the labor and material needed to build new, and maintain existing, fortifications steadily decreased.

Furthermore, the German Army was unable to realize the intended benefit of the fortifications. After withdrawal to the Siegfried-Stellung, casualties remained high throughout 1917 because OHL's defensive principles were unevenly applied and, perhaps more important, because Ludendorff was unwilling to authorize withdrawals before frontline units were depleted. Thus, at Arras in April and May 1917, German divisions steadfastly held long established, and often unfavorable, trench lines instead of withdrawing to reserve positions or the better-sited fortifications of the Wotan-Stellung.

A Reinforced Concrete Shelter Under Construction 

During the ill-fated Nivelle Offensive, German frontline units employing the new defensive tactics devastated two French armies, but as the French continued the offensive, the German victory was diminished because Ludendorff would not allow German units to withdraw before they suffered significant casualties.

Finally, the long bloody battle of Third Ypres cost the Germans dearly because, even with Lossberg directing the defense, the army could not pull back to escape British artillery fire. In all three 1917 battles, the Allies and Germans both suffered heavy casualties, but it was the Germans who could afford it the least.

When American troops first appeared on the front in late October 1917, Ludendorff decided (ironically, on 11 November) to return to the offensive, believing the time was right to defeat the exhausted British Army and bring the weary French and inexperienced Americans to the negotiating table. The 1918 spring offensives had some success, bringing the German Army within artillery range of Paris, but fresh American divisions arrived on the battlefield, denying victory and sapping German morale. By the time it became necessary for the German Army to fall back to the Siegfried, Wotan, and the other withdrawal positions, it was too weak and demoralized to properly defend them. The Allies, employing new combined arms tactics and weapons, especially the tank, were able to nullify any advantages the fortifications provided to the German Army. Germany's last line of defense was a forlorn hope. 

Source: Over the Top, January 2017, based on The Hindenburg Line, by Patrick Osborn & Marc Romanych. Highly recommended and can be ordered HERE.