On mobilisation, III Reserve Corps was assigned to the 1st Army on the right wing of the forces that invaded France and Belgium as part of the Schlieffen Plan offensive in August 1914. It was detached from 1st Army to take part in the Siege of Antwerp thereby missing the 1st Army's early battles (Mons, Le Cateau, Marne, Aisne, Arras). With the conclusion of the siege on 10 October 1914, it was assigned to 4th Army and took part in the First Battle of Ypres.