When the First World War started, the two Saxon Army Corps, and the XII (Royal Saxon) Reserve Corps were mobilized as part of the 3rd Army under command of the former Saxon War Minister, Generaloberst Max von Hausen. The 3rd Army fought in the battle of the Frontiers, mainly in the battles of Dinant and Charleroi. After the Second Army‘s retreat after the First Battle of the Marne, Hausen saw his own flank exposed and ordered a retreat. After the stabilization of the front on the Aisne River, on September 9, 1914, Hausen was relieved of his command due to illness and replaced by General Karl von Einem.
The Saxon troops were used mostly at the Western Front. As the war progressed, through the necessary additions the units becoming increasingly mixed with troops from the other German states. During the war Saxony mobilized a total of about 750,000 soldiers, of whom about 229,000 did not return.