XXV Reserve Corps was formed in October 1914. It was part of the first wave of new Corps formed at the outset of World War I consisting of XXII - XXVII Reserve Corps of 43rd - 54th Reserve Divisions (plus 6th Bavarian Reserve Division). The personnel was predominantly made up of kriegsfreiwillige (wartime volunteers) who did not wait to be called up. It was still in existence at the end of the war in the 3rd Army, Heeresgruppe Deutscher Kronprinz on the Western Front.
On formation in October 1914, XXV Reserve Corps consisted of two divisions. but was weaker than an Active Corps
Reserve Infantry Regiments consisted of three battalions but only had a machine gun platoon (of 2 machine guns) rather than a machine gun company (of 6 machine guns)
Reserve Jäger Battalions did not have a machine gun company on formation, though some were provided with a machine gun platoon
Reserve Cavalry Detachments were much smaller than the Reserve Cavalry Regiments formed on mobilisation
Reserve Field Artillery Regiments consisted of three abteilungen (2 gun and 1 howitzer) of three batteries each, but each battery had just 4 guns (rather than 6 of the Active and the Reserve Regiments formed on mobilisation)
In summary, XXV Reserve Corps mobilised with 26 infantry battalions, 10 machine gun platoons (20 machine guns), 2 cavalry detachments, 18 field artillery batteries (72 guns) and 2 pioneer companies.
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