XXXX Reserve Corps was formed in December 1914. It was part of the second wave of new Corps formed in the early stages of World War I consisting of XXXVIII - XXXXI Reserve Corps of 75th - 82nd Reserve Divisions (plus 8th 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 6th Army, HeeresgruppeKronprinz Rupprecht on the Western Front.
On formation in December 1914, XXXX Reserve Corps consisted of two divisions. but was weaker than an Active Corps
the divisions were organised as triangular rather than square divisions with three infantry regiments rather than four, but had a brigade of two field artillery regiments
Reserve Infantry Regiments consisted of three battalions but lacked a machine gun company
Reserve Cavalry Detachments were much smaller than the Reserve Cavalry Regiments formed on mobilisation
Reserve Field Artillery Regiments consisted of two abteilungen (1 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, XXXX Reserve Corps mobilised with 18 infantry battalions, 2 cavalry detachments, 24 field artillery batteries (96 guns), 2 cyclist companies and 2 pioneer companies.
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