Turning to Rawlinson's Fourth Army, which were last seen in contact with the old Hindenburg Line along its formidable front from Vandhuile on the left to Gricourt on the right, it will be remembered that it consisted of Butler's Third Corps on the left, the Australian Corps in the centre, and Braithwaite's Ninth Corps on the right in contact with the French. The time had now come for an attack on the largest scale in order to endeavour to carry this Chinese Wall of Germany by storm. The part assigned to the Third Corps in this important operation was not a large one, and their front was now contracted to 2000 yards, while two of their divisions, the Fifty-eighth Londoners and the Seventy-fourth Yeomanry, were transferred to another area. There {150} remained only the Twelfth and Eighteenth Divisions in line, which had to cover the left flank of the main attack which was to be made by the Australian and Second American Corps, and by Braithwaite's Ninth Corps to the south of them. [Sidenote: Sept. 27.] At this point the great Canal de l'Escaut passes under a tunnel which is nearly six miles in length. Thus it is the only place in the whole line where tanks could be used to advantage. The general plan was that this section of the line should be carried by the Second American Corps as far north as the northern entrance of the tunnel. This done they would extend their gains to the left in a north-easterly direction beyond Vandhuile, so as to open up a way for the Fifth Corps. After the line had been taken Australian Divisions were to move forward through the Americans and push the advantage to the east. The rôle of the Third Corps was to cover the left of the Americans, and then, when the latter had moved northwards, to mop up Vandhuile, establish bridge-heads east of that point, and bridge the canal for the Thirty-eighth Welsh Division on the right of the Fifth Corps to get across.