The battle of the Selle, 17-25 October 1918, saw the British force the Germans out of a new defensive line along the River Selle that they had been forced to take up being forced out of the Hindenburg Line. The battle of Cambrai-St. Quentin, 27 September-9 October 1918, had been Haig’s contribution to Marshal Foch’s great autumn offensive, designed to force the Germans out of the Hindenburg Line. It had succeeded, but the Allied advance had then slowed in the face of increasing German resistance, and by 10 October the Germans were taking up a new position on the River Selle, close to Le Cateau.
The British needed two weeks to prepare to attack the new position. Cambrai-St. Quentin had been a costly battle – the British had suffered 140,000 casualties during the battle, and needed time to reorganise and to bring up their artillery.
On 17 October Rawlinson’s Fourth Army attacked on a ten mile front south of Le Cateau. Their aim was to reach a line between Valenciennes and the Sambre and Oise Canal. From there the key German railway centre at Aulnoye would be in artillery range. The Fourth Army attack made slow progress – after two days the right wing had made the biggest advance, a move of five miles.
The attack was then widened. By the evening of 19 October the First Army (Horne) had fought its way into a position where it could take part in an attack north of Le Cateau. Early on the morning of 20 October the First and Third Armies attacked north of Le Cateau. By the end of the day they had advanced two miles. In earlier battles that would have been a dangerous distance to have moved, and would have placed the British right in the middle of the German fighting zone, but the fighting had moved out of the German fortified zone and into open country, and the Germans had only had ten days to build up their defences on the Selle.
Early on 23 October Haig launched a night attack with all three of his British armies, the First, Second and Fourth. This time the British advanced six miles in two days. The British were now twenty miles behind the rear line of the Hindenburg Line, and the Germans were on the back foot. They formed another new line between Valenciennes and the Sambre, but that line was penetrated on 4 November (battle of the Sambre), after which the speed of the Allied advance increased. The British advanced as far between 4-11 November as they had between 27 September and 3 November, and as the war ended the Canadians liberated Mons.