Everywhere French forces were repulsed with heavy losses, largely in encounter battles with the advancing Germans whose heavy artillery often destroyed French units long before they could bring their own lighter guns to bear. The French armies were thus already falling back when the German outflanking movement began to take effect.
The right wing of the German forces, General von Kluck’s First Army, passed through Brussels on 20 August and two days later found the Allied left flank in the industrial town of Mons. There the two corps of the British Expeditionary Force under Field Marshal Sir John French had been rushed into the line and had barely taken up their positions when they were attacked. With their French allies on their right, they were forced into a retreat that lasted for two sweltering weeks until, at the beginning of September, the Schlieffen plan came unstuck; the Allies counter-attacked; and the entire German strategy collapsed.
The story of the so-called Battle of the Marne has been retold innumerable times, and everybody involved has claimed the lion’s share of the credit. Perhaps the most cogent comment was that of Joffre, who later said that he did not know who had won the battle, but he knew who would have been blamed if it had been lost. Briefly what happened was this. Kluck had been ordered to sweep round to the west and south of Paris in order to encircle and complete the annihilation of the French armies.
But on 30 August he decided that, rather than carry out this hugely ambitious operation, he should give priority to maintaining contact with General von Bülow’s army on his left, which had been slowed down by French counter-attacks. With Moltke’s approval, he therefore deflected his line of advance to the south-east of Paris. Meanwhile Joffre had been using his railway network to switch forces from his right wing to the region of Paris, whence they now threatened Kluck’s exposed right flank. On 4 September Joffre halted the retreat of his main forces and simultaneously unleashed this new army against Kluck. When Kluck deployed to meet it, a gap opened between his left flank and Bülow’s right, into which British and French forces began to penetrate.
Von Moltke, 150 miles behind the front at Luxembourg and receiving only fragmentary messages from his army commanders, became uneasy. He had already weakened his forces by sending two army corps to the Eastern Front, where things seemed to be going badly wrong. On 8 September he sent his Chief of Intelligence, Colonel Hentsch, to see what was happening, with plenipotentiary powers to sort matters out. Hentsch found both army headquarters in a state of confusion, and confirmed their own inclination to retreat. The whole German line fell back to the line of the Aisne, the French and British cautiously following. There the Germans established themselves in positions that they were successfully to defend for the best part of four years to come.
The German Invasion of Belgium
