The advance of the 6th Argyll and Sutherland Highlanders was slower, not so much on account of the German resistance to them frontally, but on account of the fire which came from the high ground on their right flank. However, by 10 P.M. they had established themselves on the canal bank from the rubber factory south of Prouvy westwards, capturing Haulchin and releasing 1500 French civilians. This advance was materially assisted by the Corps Cyclists, who patrolled the country well in front of the infantry, and enabled the latter to advance with few delays.
After dark, at 8 P.M., the 7th Argyll and Sutherland Highlanders resumed their advance, the 4th Seaforth Highlanders on the Divisional right at 10 P.M. This advance proceeded successfully, and by midnight the leading troops had reached the eastern edges of the Grand Bois and the Bois de l’Entrée, the line running thence north-westwards to the railway leading to Denain.
Throughout the night 20-21st October, which fortunately was light and clear, the advance continued. The 153rd Brigade had already reached the canal bank throughout their front, and had formed a defensive flank on their right along the railway line facing Thiant. The 7th Argyll and Sutherland Highlanders on the right of the 153rd Brigade also made great progress. In the grey of the morning their first company entered Thiant. Here they encountered a burst of machine-gun fire, but by 9 A.M. they had beaten down all resistance, and had worked through the village as far as to the banks of the Ecaillon. They, however, found the enemy in strength on the eastern banks, and so took up positions in houses and hedgerows on the edge of the stream. At 10 A.M. 21st October they gained touch with the Canadians, who had entered Prouvy.
The 4th Seaforth Highlanders and the 11th Brigade, 4th Division, who were now up in line with them on the high ground overlooking Monchaux and the river Ecaillon, were now unable to make further progress towards the banks of the river, as they found the western sides of the river valley were very exposed and covered by the fire of the enemy holding strong natural positions in sunken roads.
During the day the field artillery moved into positions west of Thiant.
From this point onwards, as the villages in front of the line were occupied by French civilians, the Divisional commander decided only to use 18-pounder shrapnel against them. Similarly, for the same reason, gas was not employed against the villages. This was a great deprivation, as a large supply of the long awaited mustard gas had just arrived.
Naturally the Germans used gas in similar circumstances freely.
Meanwhile the bridges thrown across the Selle were only sufficient for field-guns and horsed transport. Arrangements had therefore to be made by the C.R.E., Lieut.-Colonel Napier-Clavering, to provide bridges which would enable the Corps heavy artillery and lorry traffic to keep pace with the advance, so that all weapons would be available to engage the enemy should he decide to stand on the east banks of the Ecaillon.
Reconnaissances were therefore carried out by the 400th and 404th Field Companies, R.E., at Douchy and Noyelles for sites for the construction of heavy bridges over the river Selle. In both places the enemy had destroyed the original brick bridges, totally removing the central pier and one abutment in each case. The Douchy gap measured 72 feet and that at Noyelles 88 feet. No long girders were available to bridge these gaps without piers, and the difficulty of securing foundations for the piers on the mass of brick debris in the river-bed had therefore to be overcome.
For the Douchy bridge standard girder spans of 16 feet by 18 feet were available, so that work was begun by the 400th Field Company, R.E., on the 20th. By 10.30 A.M. on the 23rd the bridge was completed for all traffic except heavy tanks, thus enabling the heavy artillery to cross the river in time to take part in the attack to be delivered on the 24th.