The first battle of the Marne had scarcely opened on 6th Sept., 1914, when von Kluck, realizing that Maunoury's force on his extreme right was becoming dangerous, sent two army corps northwards to deal with it. Maunoury had already crossed the Marne and fought the first battle of the Ourcq on the 5th. The dispatch of the two German corps to keep him in check made a way now for the British troops, when, according to plan, they turned on the invaders with the object of assailing their flank with the French Sixth Army on their left; while the French Fifth Army, and the French armies to its right, made a simultaneous frontal attack.
Both Joffre and French were under the impression that the German thrust was still in full career when their counter-stroke was delivered. Already, however, the tide had begun to turn. Von Kluck, realizing too late—what should have been obvious from the first—that his communications were being seriously threatened on the Ourcq, saw that retreat was inevitable unless he could crush the forces gathering so ominously against his right flank. The opening of the battle of the Marne thus became on von Kluck's part an effort to overwhelm Maunoury on his right, while he kept the British army and French Fifth Army at bay with strong rear-guards and cavalry. The surprise of the day to the Germans was probably the remarkable part played by the British, who, instead of being practically wiped out, as the enemy fondly believed, attacked with an energy and dash which carried everything before them, and, but for filling their allotted rôle of maintaining alignment with the French armies on each flank, would doubtless have advanced farther than they did. As it was, the progress made was considerable. The Germans were driven back to the Grand Morin, and the line of that stream made good on the following day.
Meantime the French Fifth Army on their right, materially helped by this success, had also recovered a good deal of ground, while Foch and Langle de Cary, farther east, held their own against the fierce assaults of the German centre. A last desperate effort was being made to hack a way through at this point, and Sarrail, on Langle de Cary's right, had to give way a little along the Meuse. That day the Germans reached the most southerly point of their advance, at Provins. The deciding phase of the battle, however, was developing with dramatic swiftness on von Kluck's right wing. Maunoury was hard pressed by the repeated onslaughts of the enemy, whose heavy reinforcements at this point held the issue in the balance for several days. General Gallieni, the Governor of Paris, hurried up fresh troops to Maunoury in motor-buses and taxis, and the French line held.
The British army helped matters considerably by driving the Germans across the Grand Morin at Coulommiers on the 7th, and on the following day from the Petit Morin, thus also helping d'Esperey with the French Fifth Army, on its right, to continue his advance farther east as far as Montmirail. On the 9th came the decisive blows which removed all doubts as to the issue of the battle. Von Kluck's retreat on his left flank exposed the right of von Buelow's Second Army, which was further jeopardized by a gap which appeared on its left, where it should have linked up with von Hausen's Third Army. This double opening gave Foch, facing von Buelow in the marshes of St. Gond, the opportunity which he sought of smashing the enemy's centre. He seized it by a series of lightning blows which drove the German centre back on the morning of
the 10th in complete disorder, pursued by Foch's victorious infantry.
All the reinforcements sent to von Kluck were now of no avail against the French Sixth Army, which had been fighting against odds since 6th Sept., helped not a little by Pulteney's 3rd Corps on its right flank. Maunoury carried the Ourcq on the 9th, and Pulteney's corps was able to cross the Marne, after stiff fighting at La Ferté-sous-Jouarre, at dawn on the following day, when the German retreat became general. The left of the British 2nd Corps had crossed the Marne at Nanteuil, where the bridges were found unbroken and the enemy gone, on the morning of the 9th, but was ordered not to advance too far north until the 1st and 2nd Corps were firmly established on the northern bank. The 1st crossed later in the day at Charly-sur-Marne and Saulchéry, clearing the ground of the enemy and making many captures; but the 3rd Corps had a harder task at La Ferté-sous-Jouarre, and, as already mentioned, was not completely established on the other side until the following morning. The first battle of the Marne ended on the night of the 10th with the enemy in full retreat to the north and north-east and the Allies in hot pursuit. By the 12th he had been driven back from the Seine a distance of 65 miles, and the great German plan of a sudden crushing defeat of the Allies in the West had collapsed like a house of cards.
The hopes thus raised among the Allies of a speedy termination of the war in their favour were, on the other hand, equally illusory. Though the Germans lost heavily in officers and men, as well as in guns and other war material, their retreat was no disorderly flight. Many desperate rear-guard actions were fought all along the line, but the enemy retired steadily to prepared positions on the Aisne, where the eyes of all the commanders were to be opened to the possibilities of trench warfare under modern conditions. It needed many hard lessons before the truth was driven home.
When the first battle of the Aisne opened on 13th Sept., the British army already had its outposts on that river, the main body being in positions somewhat to the south, between Soissons and Bourg. Throwing bridges across during the night, the advance was continued on the opposite bank on the following day, though not without heavy British casualties, amounting to between 1500 and 2000, including 3 commanding officers. The 6th Division arrived from England at this stage, and joined its own 3rd Corps on the left. Further advance was stayed by the strength of the enemy's entrenched positions, in which he now determined to make his stand. Here he was backed by an overpowering superiority in artillery which, with fierce counter-attacks on the part of his infantry, gallantly repulsed though they were, caused such severe losses that the British Commander-in-Chief was forced to assume a defensive rôle, while Maunoury, de Castlenau, and Foch each made stupendous efforts to break the enemy's line and renew the war of movement and manœuvre on which their military principles had been based. All, however, ended in the same dreary deadlock of entrenchments.