The German offensive was facilitated by the abnormally dry season, which reduced the strength of the water-defences of the British right, and a dense fog favoured the attack on our forward positions. The Germans got their infantry across the Oise canal north of La Fère without being noticed, and many of our outposts were surrounded before it was known that the attack had begun, although a brief bombardment by gas and other shells had drenched our line and areas miles behind it all along the front (see Map, p. 338). The forward zone resisted heroically, but by noon the Germans were through it west of La Fère and were in our battle-zone north of St. Quentin at Ronssoy. Between these two extremes of Gough's front they reached in the afternoon Maissemy, north of St. Quentin, and the line Essigny-Benay south of it. Farther north less progress had been made against Byng's Third Army, but the Germans had reached St. Leger in their effort to thrust a wedge between Arras and Cambrai, and many villages had been captured. The prospect was gloomy for the morrow, since, although the Germans had already used sixty-four divisions they were prepared to throw in fresh ones each succeeding day, and it would be several days before reinforcements could reach the Somme either from our reserves in Flanders or the French reserves in Champagne. The Germans made comparatively little headway on the 22nd against the Third Army; but Gough's last reserves were thrown in without stopping the German advance on our right, and the meagre French division which Fayolle was able to send across the Oise could not dam the torrent. At night the enemy had penetrated our third defensive position, and Gough ordered a retreat to the unfinished bridgehead on the Somme. Byng's right had to conform to this movement, which did not stop east of the Somme; for on the 23rd the Germans had crossed the river south-east of Ham, more than a dozen miles from their starting-point, and the Péronne bridgehead had to be abandoned. Even on the west bank Gough's right was thus endangered, and his left was threatened by a German attempt to break a gap north of Péronne between his army and Byng's Third. This effort on the Somme, where it runs due west from Péronne to Amiens, now became the chief and most promising objective of the German strategy. The link between our two armies was extremely fragile, and misunderstandings arose between the two staffs. Fortunately the worst disaster was averted by Byng's timely withdrawal from Monchy, which disconcerted and postponed the German attack on Arras.