The corps consisted of two or more divisions and various support troops, covering a geographical area.
Some corps areas also disposed of fortress troops; each of the 25 corps had a Field Aviation Unit (Feldflieger Abteilung) attached to it normally equipped with six unarmed "A" or "B" class unarmed two-seat observation aircraft apiece.
Originally each military district was linked to an army corps; thus Wehrkreis I took over the area that I. Armeekorps had been responsible for and sent replacements to the same formation.
The first sixteen reserve corps raised followed the same pattern; X. Reserve-Korps was made up of reservists from the same area as X. Armeekorps.
However, these links between rear areas and front line units were broken as the war went on and later corps were raised with troops from all over Germany.