On mobilisation, XVII Corps was assigned to the 8th Army to defend East Prussia, while the rest of the Army executed the Schlieffen Plan offensive in August 1914. It took part in the battles of Gumbinnen, Tannenberg and 1st Masurian Lakes. Immediately after the latter, it joined the 9th Army in Lower Silesia, where it fought at the Battle of the Vistula River.