Thanks to General Foch's further activities, General von Bülow had troubles upon his left wing. When dawn of this same day or torrential rain, September 9, 1914, broke over the hill-road that runs from Mareuil to Fère-Champenoise, at which point lay the left of General von Bülow's army, it witnessed a number of 75-millimeter guns on selected gun sites commanding the right flank of the German right center. General Foch's daring, the success of the maneuver, and the fact that the conduct of all the French armies on that day and the day following seems to be with the full cognizance of this venture, led inevitably to the conclusion that those brilliant feats, conceived by General Foch, had been communicated to General Joffre in time for the French General Staff to direct the French armies to the right and left of General Foch to cooperate with his action. Had General Foch been less ably supported, his wedge might have proved a weak salient open to attack on both sides. But General Foch's main army to the west kept General von Bülow busy, and General Langle's army to the east fought too stubbornly for the Duke of Württemberg to dare detach any forces for the relief of General von Bülow. General von Hausen's Saxon Army was weak, at best.
What were the forces that operated to make this particular point so weak are not generally known. As, however, the divisions from Alsace were much in evidence three or four days later, it is more than probable that these divisions were intended for service at this point, and also to reenforce General von Kluck's army, but that, by the quick offensive assumed by General Joffre on the Ourcq, and, owing to the roundabout nature of the German means of communication, these expected reenforcements had not arrived. The German official dispatches point out that General von Bülow's retreat was necessitated by the retreat of General von Kluck. Of this there is no doubt, but even military necessity does not quite explain why General von Bülow bolted so precipitately. His losses were fearful, and the offensive of General Foch rendered it necessary for the Germans to fall back on the Aisne.
The armies of the Duke of Württemberg and of the crown prince may be considered together, for they were combined in an effort to pierce the French line near the angle at Bar-le-Duc. General Langle held on desperately against the repeated attacks of the Duke of Württemberg. Ground was lost and recovered, lost again and recovered, and every trifling vantage point of ground was fought for with a bitter intensity. Though active, with all the other armies, on September 5 and 6, 1914, it was not until September 7 that General Langle found himself strained to his utmost nerve. If he could hold, he could do no more, and when night fell on September 7, no person was more relieved than General Langle. Yet the next day was even worse. Instead of slackening in the evil weather, the German drive became more furious. The exhausted Fourth Army fought as though in a hideous nightmare, defended their lines in a sullen obstinacy that seemed almost stuporous, and countercharged in a blind frenzy that approached to delirium. It was doubtful if General Langle's army could hold out much longer. But, when General von Bülow was compelled to retreat, when General Foch turned his attention to General von Hausen's Saxon Army, and when General Joffre found himself in a position to rush reenforcements and reserves to the aid of General Langle, a new color was given to the affair. The defense stiffened, and as rapidly as it stiffened, so much the more did it become patent that the Duke of Württemberg could not afford to be in an exposed position far in advance of all the other attacking armies. Wednesday, September 9, 1914, revealed to the German center the need of falling back on the crown prince's army, which was the pivot on which the whole campaign swung.