The First Battle of the Marne
By the end of August most of the Allied forces had been forced to fall back towards the Marne River, east and southeast of Paris. French and British commanders were in open disagreement over supposed failings on both sides and the British Secretary of State for War, Field Marshal Herbert Kitchener, had been forced to intervene. As the German 1st and 2nd Armies approached Paris they swerved southeast, away from Paris, in a bid to swallow the retreating French armies. In the process they exposed their right flank.
This was an opportunity Joffre was quick to seize. He laid plans to attack the Germans along the length of the front with his Sixth Army of 150,000 men and the BEF's force of 70,000, on the morning of September 6. Realizing the danger, on September 5, Von Kluck's 1st Army began to turn to face the west, the direction of the coming attack. The First Battle of the Marne began a day sooner than Joffre had planned. The German turn had created a 30-mile gap between the German 1st and 2nd Armies, reported gleefully by the crews of Allied reconnaissance aircraft. Troops from the BEF were dispatched to join the French Fifth Army in pouring through the gap. At the same time, the Fifth Army attacked von Bülow's 2nd Army in an effort to pin it down.
Between September 6 and 8, the Germans were still hopeful of a breakthrough against the French. The success of the German drive now hung in the balance. Joffre now ordered all French troops in Paris to march immediately to the Marne and join the 6th Army. Every form of available transport, including the Paris taxicab fleet, was pressed into service to move some 10,000 men to the front. The taxi drivers kept their meters running and when the battle was over they presented their bill. The French government paid the bill without protest.
A surprise attack by the French Fifth Army of Franchet d'Espèrey against the German 2nd Army, on September 8, widened the gap between the two German armies. It was a rapid success for Franchet d'Espèrey, who had succeeded Lanrezac, fired for his lack of attacking spirit.
By September 9, it was looking as if the German armies would be encircled and destroyed. The situation looked so desperate to the commanding officer, Chief of Staff Helmut von Moltke, that he suffered a nervous breakdown. A general retreat to the River Aisne was ordered where German forces planned to regroup. The German strategy of encircling and destroying the French Army had failed. "Six weeks to Paris and Victory", seemed little more than a dream. The Schlieffen Plan lay in tatters.
Troop Deployments at the First Battle of the Marne
One of the perennial topics of debate among World War I strategists is whether Moltke's revisions to Schlieffen's original plan ultimately led to its failure. If only Moltke had left well enough alone, it's been argued, the Schlieffen plan would have achieved its objective. There is no question that Moltke's revisions weakened the German forces on the Western Front and especially the right wing that was charged with breaking through the French lines and sweeping into northern France.
There are a number of extenuating circumstances that need to be weighed as well, however. First, no military plan, however well thought out, remains static for a decade. Conditions change. The political environment, each side's capabilities, an opponent's plans and responses all invariably force revisions. In 1905, Russia, having just been defeated by Japan in the Russo-Japanese war, posed far less of a threat to Germany than it would a decade later. Great Britain's eventual role was far less certain in 1905, than it would turn out to be in 1914. Moreover, the deployment of forces envisioned by Schlieffen in 1905 never actually existed. Schlieffen assumed a level of German strength that in 1905 was at best theoretical and at worst little more than wishful thinking. Moreover, it's worth emphasizing that notwithstanding the revisions that were made, the German General Staff still committed over 90 percent of its troop strength to the Western Front. Perhaps a few more divisions might have been the margin of victory and then again, it might not have made a difference. In the end, such is the fog of war.
On the other hand, there is no question that Moltke's unwillingness to cede German territory on either the Eastern Front or in Alsace-Lorraine changed one of the fundamental assumptions of the Schlieffen plan. Schlieffen had anticipated that French forces would be pulled deep into Alsace where they would not only be further removed from their defensive fortifications along the border, but also less able to help the French armies meeting the German right wing further to the west. By weakening the German right wing and strengthening the German center and left wing, Moltke short-circuited one of the key assumptions of Schlieffen's plan. The question of whether the Schlieffen plan could have worked and the consequences of Moltke's revisions to them will not be resolved here. It will remain instead a topic of heated debate and countless speculations among armchair generals.