August 10, 1918, was a notable day for the French forces when Marshal Foch threw his First Army against the apex of the German salient southeast of Amiens. Montdidier was captured, and the salient was smashed in to an average depth of six miles on a thirteen-mile front, reaching a line extending from Andechy to the northeast of Montdidier to Elincourt, ten miles to the southeast. From Albert to the southern side of the Montdidier salient the whole Allied line was pushed eastward, reaching a maximum distance in the direction of Chaulnes, the principal railroad center of the Germans west of the Somme River.
The French launched their attack without any artillery preparation in the sector east of Montdidier between Courcelles-Epayelles and the Matz River. The Germans were on the alert, but the dash and suddenness of the French attack overcame their most determined efforts. In one hour after the French went forward their first objective, Ressons-sur-Matz, was won, and in the succeeding two hours they had captured Mortemer, Cuvilly, and Marqueglise. At some points the advance was five miles. By noon on August 10, 1918, the Germans in Montdidier found that they had been caught in the jaws of a trap. Converging French attacks from the north and south had succeeded in practically encircling the town. The French drive had also deprived the Germans from using the Montdidier-Chaulnes railway, which was the only line that supplied food and material to their fighting front at the bottom of the Montdidier pocket.
By the capture of Faverolles, which was stormed by the French in the morning of August 10, 1918, the Germans were hampered in their withdrawal of troops from Montdidier. The day closed with Von Hutier's forces in hurried retreat from the Montdidier-Noyon line.
The Allies had made their great advance with only moderate losses. The casualties, including killed, wounded, and missing, numbered less than 6,000, or not more than a fourth of the number of prisoners taken. In the course of the fighting eleven German divisions had been defeated and so badly cut up that a long time must elapse before they would be in a condition to be re-formed and ready for serious work.
North of the Ancre River the British had firmly established their positions and were pushing out patrols in the direction of Bray. In their advance south of the Somme they captured Warvillers, Vrely, Folies, Rozières, and Vauvillers. To the north of the Somme, where they were aided by the brilliant fighting of the Americans, Chipilly Spur was the scene of a determined struggle. After winning the Spur the Allies pressed on, driving the Germans before them. An interesting feature of the day's advance was the capture at Lihons of a complete German divisional headquarters and staff.
The Germans showed more than common ingenuity in devising traps to hinder the advance of the Allies. In many instances a large number of shells would be placed in pockets under the roads so arranged that the weight of a passing wagon or motor lorry would explode them. They also arranged barbed-wire entanglements so that attacking troops would explode mines, but the Allies had learned through bitter experience the gentle ways of the enemy, and took effective means to render the German traps ineffective. Poisoned food and poisoned water marked the enemy's backward trail, but the Allies had long before concerted measures to protect the troops from such Teutonic pleasantries.
The Allies continued to fight their way forward during the night of August 10, 1918, and on the following day the armies of Von Hutier and Von der Marwitz were in full retreat in the direction of Péronne, Nesle, and Ham. Important rear guards were sacrificed by the Germans to secure the safety of their main armies, and it became increasingly evident that they were running out of reserves.
The Allied line on the front from Albert south to the Oise was carried forward, especially to the south, where the French were operating by themselves. During the night Haig's troops advanced their line on the high ground between Etinehem and Dernancourt. Farther south on the other side of the Somme the Germans, having received reenforcements, delivered powerful attacks against the British positions at Lihons and succeeded in making a temporary breach in the British line. In a fierce counterattack the British drove them back with heavy losses and the line was completely restored.
The capture of the Massif of Lassigny by the French on August 12, 1918, was of first importance to the Allies, for the heights command a broad sweep of difficult country and when in German hands were a formidable obstacle to the Allied advance.
German positions at Roye were now threatened on three sides—north, west, and south—as the Allies pushed their lines forward. The British gained ground to the east of Fouquescourt, while the French captured the village of Armancourt, and Tilleloy and the Bois des Loges.