The battle of Sambre (or Charleroi), 21-23 August 1914, was perhaps the most important part of the wider Battle of the Frontiers of France (First World War). The German war plan, based on the Schlieffen Plan, was for three German armies to sweep through Belgium, bypassing the fortified Franco-German border. Those armies would then continue their advance south and south west towards Paris, before turned east to pin the main French armies against the German or Swiss borders. In contrast the French had planned to launch an invasion of German through Alsace-Lorraine. When war broke out five French armies were lined up along France’s eastern border, with the Fifth Army, under General Charles Lanrezac at the north of the line.
Lanrezac’s army began the war at the southern end of the Franco-Belgium border. General Joffre, the French Commander in Chief, did not expect the Germans to advance through northern Belgium, and even after the German violation of Belgium neutrality remained convinced that any attack would come south of the Meuse. Lanrezac did not share this opinion, and repeatedly warned Joffre about the possibility of a German attack that would outflank the entire French line. Finally, between 14 and 20 August Joffre began to share some of his concerns. The Fifth Army was ordered to move north to guard the line of the Sambre River, a tributary of the Meuse. The French were still taking up their positions on the Sambre when the Germans attacked.
Joffre had been entirely wrong about the German plan. Two entire German armies, the First under General Alexander von Kluck and the Second under General Karl von Bülow, had crossed the Meuse into northern Belgium, and were sweeping around the exposed left flank of the French line, while the Third Army under General Max von Hausen was approaching along line of the Meuse. The French Fifth Army, supported only by the tiny but professional BEF, was about to face an attack by three entire German armies.
Lanrezac’s plan was to defend the high ground south of the Sambre, while leaving small outposts to defend the bridges across the river. Unfortunately French intelligence about the river was woeful, misreporting even the number of bridges. When the Germans reached the river, they found a number of undefended bridges.
Aware of the dangers of attacking across a river into the line of villages along the Sambre, the Germans were planning a combined attack by the Second and Third armies. The Second would attack from the north, across the Sambre, the Third from the east, across the Meuse, trapping the French army in a pincer manoeuvre. This plan was pre-empted on 21 August. The first German units to reach the Sambre, from the Second Army, found a number of undefended bridges. Two units, the 2nd Guard Division and the 19th Division, successfully crossed the river and gained control of two large bends in the river.
This need not have been a problem for Lanrezac, who still held the line of higher ground, but on 22 August he gave two of his subordinate commanders’ permission to launch a counterattack. Nine French divisions attacked three German divisions and suffered a bloody repulse. A dangerous gap was now beginning to develop on Lanrezac’s right, between the Fifth and Fourth Armies.
On 23 August Lanrezac attempted to launch a further counterattack, but without success. Meanwhile the Germans forced their way across the Meuse, close to its junction with the Sambre, threatening Lanrezac’s right wing. On his left the BEF held off the German First Army at Mons, but by the end of the day Lanrezac was in danger of being cut off. At 11.00 pm on 23 August Lanrezac ordered the retreat. With their French allies in retreat, the BEF was also forced to pull back. The retreat would last for the next two weeks.