On retiring, the corps was attached to the French Fifth Army during the Battle of Charleroi (21-3 August) and the Battle of Mons (23 August). By the end of 22 August, Lanrezac, commander of the Fifth Army, reported that Sordet's corps was "greatly exhausted" and that it had had to pull back, helping to open a gap of – enough for an enemy corps – between Fifth Army's left and the right of the BEF. Together with the news which reached him at noon next day that Belgian 4th Division were evacuating Namur, this helped decide Lanrezac to pull back from his position at Charleroi.