The second stage of Foch's plan now had been reached. The German armies had again been brought back to the line which they had chosen in 1914, after their first rush had recoiled. It was less threatening by the loss of the St. Mihiel salient, but it had been enormously strengthened by four years of engineering. North of the defence line was the railway which, running through Brussels, Mons, Maubeuge, Mézières, Sedan, and Metz, was the chief artery of German communications, and Foch's plan was to cut this artery on either side of the great curve which the German line made when, after coming north to south from the coast, it turned west to east at La Fère. The right half of the thrust was to be made by Gouraud's army at Rheims and the Americans on the Argonne, where they were being steadily accumulated. The more deadly attack was to be made by the First, Third, and Fourth British, and the First French Armies, which should break through Cambrai and St. Quentin towards Maubeuge.
Complementary operations were designed for the armies of Humbert and Mangin at the nose of the curve, and it was expected that, under this comprehensive pressure, Ludendorff would be compelled to withdraw divisions from the coastal sector, where an attack by the British Second Army (Plumer) and the Belgian Army might then be successful against a weakened front. A portion of Degoutte's army was sent northward in readiness for such a blow, and to the Fifth British Army (now commanded by Birdwood) was assigned a task at Lille and Lens similar to that of Humbert and Mangin at St. Gobain.
There was a pause of nearly a week, in which the Germans awaited, and the Allies prepared the new move; and then, on 27th Sept., Haig's armies struck what Foch declared to be the blow from which there was no recovery. The battle of Epéhy had given the requisite positions for the attack on that section of the Hindenburg defences which the Germans named the Siegfried line. The plan was to send forward the First (Horne) and Third (Byng) British Armies to clear the way on a line from Sauchy-Lestrée to Gouzeaucourt, seizing the crossings of the Canal du Nord, and so preparing the way for an attack by the Fourth Army. The dangerous movement was accomplished (27th Sept.): the crossings seized, the canal held, and Cambrai threatened. On 29th Sept. the Fourth Army took up the combat, and in a tremendous action along a front of 20 miles, supported by attacks from the other British armies and the First French Army, got across the vital defences of the St. Quentin Canal in the Siegfried zone. The next day the fighting spread furiously along the front of all four armies: the breach was widened; a portion of the Scheldt Canal taken; and by 3rd Oct. the Fourth Army had pierced the Siegfried line vitally. By 9th Oct. the German defences
were no longer defences, and in this decisive encounter they had lost 36,000 prisoners and 380 guns.
Elsewhere victories had been won which appear minor only by comparison. American divisions had been transferred to the left bank of the Meuse at Verdun, and, supported by French divisions, had carried Montfaucon and Varennes (10,000 prisoners); on the other side of the Argonne Gouraud was advancing, and by 1st Oct. was 9 miles from his starting-point below Moronvilliers, and had accumulated 13,000 prisoners and 300 guns.
The results of these attacks were at once apparent, as Foch had predicted, in the north. His plan of an attack by Plumer's Second British Army, and by the Belgian Army stiffened by French divisions, was as successful as he had hoped. Under the weight of the Franco-Belgian-British attack on 28th Sept. the thinly held German front melted away. By nightfall the British held all the ridge between Wytschaete and the canal north of Hollebeke; the Belgians were in Houthulst Forest. By the end of September the blood-drenched ridge of Passchendaele, and all its tragic surroundings, had passed into the Allies' hands, and the German grip on the coast had been finally unloosed. This marked the beginning of the end. Since Foch attacked between the Aisne and the Marne on 15th July the Allies had taken a quarter of a million prisoners, 3669 guns, and 23,000 machine-guns. The rest of the campaign must either be a disaster of the first magnitude to the Germans, or, at best, a painful and ineffective retreat to the line of the Meuse.
What remained of the campaign was the work of clearing up; but this was not an easy task,