Following the defeat of the Western Allies at Charleroi and at Mons, the British Expeditionary Force withdrew past Maubeuge, their base of operations after arriving in France. On 24 August 1914, the advancing Germans arrived at the fortresses of Maubeuge and laid siege to its garrison of 45,000 soldiers. The next day, the VII Reserve Corps were left behind the main German armies to take the city. Bombardment of the forts began on 30 August, with KMK Battery 3 tasked with reducing Fort Sarts, but it mistakenly shelled an interval fortification in front of Sarts. By 5 September, a hole in the fortress ring had been opened by German 21 cm guns, but they had by now exhausted their ammunition supply. To widen that gap, the siege guns then expended their remaining ammunition against Forts Leveau, Héronfontaine, and Cerfontaine on 7 September, and destroyed them in quick succession. The two remaining French forts surrendered that same day and the Germans occupied Maubeuge on 8 September.