XXIII 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 dissolved on 12 August 1918.
On formation in October 1914, XXIII 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, XXIII Reserve Corps mobilised with 26 infantry battalions, 8 machine gun platoons (16 machine guns), 2 cavalry detachments, 18 field artillery batteries (72 guns) and 2 pioneer companies.
Cron, Hermann (2002). Imperial German Army 1914-18: Organisation, Structure, Orders-of-Battle [first published: 1937]. Helion & Co. ISBN1-874622-70-1.
Ellis, John; Cox, Michael (1993). The World War I Databook. Aurum Press Ltd. ISBN1-85410-766-6.
Busche, Hartwig (1998). Formationsgeschichte der Deutschen Infanterie im Ersten Weltkrieg (1914 bis 1918) (in German). Institut für Preußische Historiographie.
Histories of Two Hundred and Fifty-One Divisions of the German Army which Participated in the War (1914-1918), compiled from records of Intelligence section of the General Staff, American Expeditionary Forces, at General Headquarters, Chaumont, France 1919. The London Stamp Exchange Ltd (1989). 1920. ISBN0-948130-87-3.
The German Forces in the Field; 7th Revision, 11th November 1918; Compiled by the General Staff, War Office. Imperial War Museum, London and The Battery Press, Inc (1995). 1918. ISBN1-870423-95-X.