At 4.40 A.M. on the 21st of March the enemy opened an intense bombardment along practically the whole front of the Fifth and Third Armies, using a great quantity of gas shells. The infantry attack, launched in a thick fog after several hours of this bombardment, developed on the XVIIIth Corps front about 10.30 A.M. By noon the line had been penetrated at various points, although on all parts of the front isolated detachments held out most gallantly. The infantry of the 20th Division was ordered at 1 P.M. to concentrate behind the rear zone defences, and the artillery brigades moved forward to their allotted divisions, the 91st (Lieut.-Colonel Erskine) to the 36th Division and the 92nd (Lieut.-Colonel Balston) to the 30th. In the course of the day the enemy pushed forward, particularly on the right of the Corps line, where by 3 P.M. the situation had become critical. The 61st Brigade (Brig.-General Cochrane) was ordered therefore to man the bridge-heads at St Simon and Tugny immediately on arrival in that area. Pressed on the front and outflanked on the right, the 36th Division retired during the night south of the Somme. The 61st Infantry Brigade and the 91st Field Artillery Brigade covered this retirement, and from that time came under the orders of the 36th Division. Here we will leave them for the moment in order to trace the movements of the rest of the 20th Division during the following four days. On the left the Germans had penetrated the line at the junction of the XVIIIth and XIXth Corps and at Roupy, and had gained a footing in Grand Seraucourt. The 60th Brigade (Brig.-General Duncan) therefore pushed out covering troops on the defensive line from the Somme to Vaux, and as troops of the 30th Division were retiring on the left, the 59th Brigade (Brig.-General Hyslop) manned the defences between Vaux and the Corps left boundary at Trefcon. The 92nd Field Artillery Brigade under the 30th Division was in action south of Fluquières, covering a line between Roupy and Savy. All details were formed into a Divisional Reinforcement Battalion under Major Storr, second in command of the 12th King’s, and moved to a position between Matigny and Douilly. The 11th D.L.I. concentrated at Golancourt and sent “D” Company to reinforce the 61st Brigade. Divisional Headquarters came forward to Ham. This was the situation on the night of the 21st, when the enemy had advanced west and south-west of St Quentin for a distance of about three miles. Although he had made an important advance along the whole front, he had not yet broken through the battle zone.