There were some changes of troops at this date in {143} preparation for the big attack upon the Hindenburg switch line which was impending. The Twenty-second Corps (Godley) now formed on the left of the Canadians, took over the Fifty-first Division, and also occupied the south bank of the Scarpe with the Eleventh Division. It retained the Forty-ninth Division (Cameron) in reserve. On the other hand, the Fourth British Division was attached to the Canadians, and came into their centre at Remy and Haucourt. At dawn on August 30 the Canadian First Division attacked Upton Wood and the trenches near, with the object of straightening the line and maintaining close touch with the Seventeenth Corps on the right. This movement was splendidly successful, and 500 prisoners were taken. The Fourth British Division advanced at the same time and their line in the evening was just east of Eterpigny. Next day they were held up once at St. Servin Farm, but took it at the second attempt. Meanwhile, the Eleventh Division was moving steadily forward on the south bank of the river. It was relieved on October 1 by the Fifty-sixth London Division, acting under the Twenty-second Corps. On September 1 the Canadian Corps was outside the Arras-Cambrai Road, with the Fourth British Division forming its left flank, the Fourth Canadian its centre, and the First Canadian on the right. It was a day of local attacks and bickerings, but great preparations were on foot for the morrow. The first light of dawn had hardly begun to glimmer in front of the eager lines of infantry before the signal was given for the advance upon the Drocourt-Quéant line. This line is not the main Hindenburg Line, but it is a northern extension of the Hindenburg system, {144} and it may be said to cover the towns of Douai and Cambrai. The advance of the First Army was on a front of five brigades--one belonging to the British Fourth Division on the left, and two of each first line Canadian Division to their right. The general idea of the day's operations--among the most important of the war--was to break through the German line upon a narrow front, and afterwards to roll up the flanks of the enemy, both north and south. This having been done, the main attack was to push through, seize the higher ground overlooking the Canal du Nord, and if possible cross the Canal and seize the farther bank. [Sidenote: Sept. 2.] The attack should be from the Sensée River, southwards, and the function of the Twenty-second Corps was to form a defensive flank on the left of the attack, taking up consecutive positions eastwards along the River Sensée, and working in close collaboration with the British Fourth Division.