The Corps was perhaps the most useful and cohesive of the various high-level formations used by the Grand Army of the Republic and the Imperial Army—large enough to take most enemy worlds, it remained a key component in the armies of both the Clone Wars and the Galactic Civil War.
Army Corps in the Clone WarsEdit
In the Clone Wars, a standard Army Corps consisted of four Legions of Clone troopers, 36,864 men in total; it was commanded by a Clone Marshal Commander and a Jedi General. Four Corps in turn formed a Sector Army.
However, a number of formations that would strictly be subordinate Legions within these Corps also used the term "Corps" in their designations. This may possibly reflect their growth into autonomous units of Corps size on their own, but at least some of them remained part of their parent Corps even when called "Corps" themselves—making it often very hard to know whether a unit was a Corps or a Legion in terms of its place in the hierarchy, or its number of troops. In practice, the situation was probably very fluid, with various legions in various stages of evolution, with extra troops, increasing autonomy from their parent Corps, and new Corps designations of their own.
One unit that was certainly a Corps was the 9th Assault Corps—because Commander Gree's 41st Elite Corps was one of its subordinate Legions. The 21st Nova Corps, the Galactic Marines led by Commander Bacara and Ki-Adi-Mundi, were also probably a Corps within the 4th Sector Army at some point in their existence, but the 327th Star Corps, led by Commander Bly and Jedi Master Aayla Secura, is officially a corps, as it includes the 7th Legion.
Army Corps under the EmpireEdit
The Imperial Army was a much larger war machine than its predecessor had been, and composed largely of recruits from the civilian population rather than warrior clones. The white-armored elite troops who had been the backbone of the GAR had now been separated from the regular Army, and formed into a distinct arm known as the Stormtrooper Corps: as its name suggests, this was now organized as a single massive Corps, divided directly into component Legions, which could be assigned to Sector Group commands.
Within the rest of the Army, however, Corps-level units retained a significance comparable to that which they had held during the Clone Wars. Many Corps had their headquarters aboard a massive KDY-Evkamar military transport, which served to coordinate subordinate units on various planets and warships across the sector, and a barracks for troops in transit from one assignment to another. The same ship could also carry an entire Corps into orbit for a planetary-assault deployment, a single Corps was regarded as a sufficient force to reconquer a planet that had thrown off Imperial rule—typically, in the face of odds of more than four to one.
A typical Corps in the Imperial Army was still divided into four multi-regiment tactical formations, but these were known as Battlegroups rather than Legions; and often, these Battlegroups were reorganized from Divisions which had been under planetary or sector command in the days of the Old Republic.
There were four standard types of Corps—Line Corps, Armor Corps, Assault Corps and elite Atrisian Corps; and one Corps of each type formed a standard Army; but there were also autonomous Corps HQs, which functioned in a rather different way.
Composed of three Line Battlegroups and one Reinforced Battlegroup, this was essentially an infantry Corps with some embedded transport, artillery and armor support. It could field 48,514 front-line troopers from a total muster of 69,199 men, with 2,599 transports and at least 371 armored vehicles
An Armor Corps consisted of three Armored Battlegroups and one Mobile Battlegroup—a total of 48,192 soldiers and 74,794 men overall, with a minimum of 1,292 armored vehicles and 5,128 transports. It was a heavy assault formation, designed to crush resistance, push forward through the enemy, and retain control of the territory it had taken.
A Mobile Corps was supposedly designed more for maneuver warfare than the sort of frontal assaults that an Armor Corps was typically deployed in; but in practice, its three Mobile Battlegroups and one Armored Battlegroup were little different in their overall balance of armored vehicles and transports than the elements of an Armor Corps, and the two types of unit could be used interchangeably. A Mobile Corps mustered 48,504 combat personnel from a total of 71,615, with 5,548 transports and at least 1,113 armored vehicles.
With two Reinforced Battlegroups, one Armored Battlegroup, and one Line Battlegroup, an Atrisian Corps was an elite unit with a balance of firepower and infantry, with a better assault capability than a Line Corps, but more able to deploy troops in large numbers to hold terrain than an Armor or Mobile Corps.
A Corps HQ consisted of fifteen senior adjutants and 388 support personnel, guarded by a security company and six picket platoons, and burdened with 50 ISB agents and three CompForce support platoons. As its name suggests, a Corps HQ served as the administrative and organizational center of each Corps—but there were, in fact, far more Corps HQs than there were Corps in the Imperial Army, as a Corps HQ, complete with a Major General in command, also served as the key military component of the typical planetary garrison.
Such HQs provided a basis around which a Corps-strength unit could be improvised in a crisis with whatever troops the Sector Army might be able to spare; the rest of the time, it was often said that they offered very pleasant assignments for very average Major Generals. Under normal circumstances, much of the garrison commander's duties were taken up with representing Imperial authority on his planet, and acquiring leverage over the civilian diplomatic, trade, and research personnel attached to his command; but he also had four battalions of troops at his disposal to maintain order and hold the line until help could arrive. While barely amounting to the equivalent of a single regiment, it is suggested that this detachment was a powerful mobile unit, typically consisting of something like a battalion of stormtroopers, two battalions of AT-ATs, and one of AT-STs, coupled with a Ground Support Wing of two TIE/gt squadrons, one TIE/sa bomber squadron and a TIE/fc spotter flight.
This balance of forces would have given the Corps HQ garrison an impressive combination of firepower, armor, reconnaissance, and maneuverability for its size. However, it is hard to conceive of the nearly 200 tanks and almost as many support vehicles of an armored brigade fitting inside the prefabricated garrison base that was the physical presence of a Corps HQ, and the another Rebel source, discussing the garrison base in detail, implies a deployment of just ten AT-ATs and ten AT-STs.
The same source suggests that a typical garrison's Ground Support Wing, nominally of 40 TIEs, comprised in practice three squadrons of whatever TIE Fighters were available, plus a flight of two TIE Bombers, with more bombers being added if the situation warranted them: this ties in with The Imperial Sourcebook's references to Army commanders having difficulty obtaining their correct compliment of TIEs, and adds weight to the evidence of this source's analysis.
Turning back to the armored units, the smaller figures can best be interpreted as representing a single armor company, with three tank platoons where The Imperial Sourcebook speaks of three battalions: two heavy platoons of five AT-ATs each, and one light platoon of nine AT-STs, plus a tenth AT-ST as a company command vehicle. It is unusual to find heavy and light armor mixed in this way, however, and it is possible that these armor platoons were designed as cores around which larger units could be formed as required: three battalions would form the basis of an armor regiment, and with this in mind, we can note the 40 speeder bikes cited as part of the garrison, which suggest the presence of a scout troop that could serve as the basis of an armor regiment's repulsorlift battalion.