The Devil army is divided into Legions. Each Legion is specialized in one particular job. Be it conquest, infiltration, scouting or military domination.
The most known Devil legions are:
Legion I – The Reapers (aka Harvesters)
Legion II – The Magi (Imps)
Legion III – The Dominators (Cavalry)
Legion V – The Tyrants
Legion VI – The Scouts (Rangers)
Legion X – The Conquerors (Legionnaires)
Legions IV, IX, XXV – The Breeders (crossroad devils, Erynies, Ambassadors)
The Legions are housed on several Infernal planes and when a member is slain they are reborn on the lower levels of their headquarters after 1d4+1 days. As a result the Headquarters are designed as impenetrable fortresses. Usually the higher ranking members and the leader defend the fort itself and even at overwhelming opposing forces the fort does not fall.