Charleroi and Mons
By 20 August, Lanrezac's Fifth Army had begun to concentrate on a 40 km front along the Sambre, centred on Charleroi and extending east to the Belgian fortress of Namur. On his left, the Cavalry Corps of General Sordet linked the Fifth Army with the British Expeditionary Force at Mons. Lanrezac's army of 15 divisions, weakened by the transfer of troops to Lorraine, was confronted by the 38 German divisions from the Second Army (General Karl von Bülow) and Third Army moving south-west.
Nevertheless, Joffre ordered Lanrezac to attack across the Sambre. Before he could act on the morning of 21 August, the German Second Army launched the Battle of Charleroi with assaults across the Sambre, establishing two bridgeheads which the French, lacking artillery, were unable to reduce. Bülow attacked again on 22 August with three corps against the entire Fifth Army front. Fighting continued on 23 August when the French centre around Charleroi began to fall back.
Meanwhile the German Third Army had crossed the Meuse and launched a frontal attack against the French right, held by a corps commanded by General Louis Franchet d'Esperey. The Third Army attack threatened to cut off Lanrezac's line of retreat but Franchet d'Esperey's force stopped the German advance and delivered a successful counter-attack. However, with the evacuation of Namur and news of the French Fourth Army retreating from the Ardennes, Lanrezac ordered a withdrawal.
On 22 August, BEF patrols encountered the cavalry screen of the German First Army of General Alexander von Kluck near Soignies south-west of Brussels. The British Commander-in-Chief Field Marshal Sir John French initially ordered an attack, believing he was confronted by an inferior force. In truth the BEF of four infantry and one cavalry divisions, 80,000 men, faced over 160,000 German troops — the mass of Schlieffen's right wing. Fortunately for the British, on the night of 22 August French chose to take up defensive positions along the Mons-Condé Canal.
The Battle of Mons began on 23 August when Von Kluck, required to maintain contact with Bülow's Second Army on his left, launched a frontal attack on the British line with the main weight falling on the British II Corps of General Horace Smith-Dorrien. The massed rifle fire of the professional British soldiers — the Old Contemptibles — inflicted heavy casualties on the Germans who attacked en masse over terrain devoid of cover. The British held up the German advance until the evening when, now aware of the size of the opposing force, and with Sordet's cavalry in retreat leaving the right flank exposed, they began retiring to a second defensive line. For the moment, Von Kluck made no attempt at pursuit, allowing the BEF to disengage on 24 August.
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