The Arm is a puppet organization that operates under the command of an army of powerful, genetically enhanced supersoldiers known as Orion's Spear. These supersoldiers were originally tasked with eliminating any and all threats to early human interstellar expansion, and protecting colonial settlers as they terraformed hostile worlds. However, the genetic enhancements each soldier received were dangerously unstable, mutating them in a way that they no longer resembled humans. These mutations began to drastically alter the soldiers both mentally and physically, causing them to become increasingly violent. Eventually, these supersoldiers went rogue, fleeing beyond the farthest reaches of US Imperial space and vowing to destroy the US Empire and all of its citizens.
Thus, the US Empire was forced to destroy this dangerous army of supersoldiers, sending a battalion of newly formed Armored Infantry soldiers to eliminate them. This battalion was nearly wiped out and nothing was ever heard of the mutated supersoldier army again. In fact, many Armored Infantry soldiers defected to the service of the Orion's Spear, using their expertise and connections to the US Imperial military to slowly build up a proxy force called the Arm of Orion.
Having been formed by former members of the 8th Armored Infantry Division, or Section 8, the Arm holds expert knowledge of Armored Infantry tactics taken from one of the US Empire's most feared military units. They are experts in the risky deployment method of Burning-In, dropping from incredible heights to fall upon their enemies with utter lethality. Once deployed, Arm units employ the same brutal shock tactics employed by Section 8, using on-demand, orbital-dropped emplacements and vehicles to devastating effect.
However, one major difference has been shown between the units of the Arm and their Section 8 counterparts: They are far more brutal. It has been shown in the Section 8 game that the Arm does not hesitate to commit wartime atrocities against civilians, such as attempting to launch a nuclear missile at a civilian settlement on New Madrid, even when in the midst of intense battle with USIF troops.
In addition, the Arm has managed to reverse-engineer the advanced weapons, equipment, and vehicles used by Section 8, including powered armor that duplicates the technology found in USIF Powered Assault Armor. This allows them to fight any US Imperial forces on equal terms.
In order to topple the United States Empire, the Arm attempted to spread terror throughout the Outer Rim colonies by first disabling each planet's Titan Array, starting with weakly defended planets in the Clavius System. With each planet's main line of communication down, the Arm would rapidly move to conquer the world, plundering colonies for resources and technology. A short time thereafter, the Arm had completely overrun the Clavius System.
However, the sudden loss of a star system drew the attention of USIF Military Headquarters, who dispatched a Battlefleet to investigate, spearheaded by the 8th Armored Infantry Division. When the Battlefleet arrived in the system and held orbit over New Madrid, it was met by heavy fire from Arm anti-orbital cannons. This marked the beginning of a series of battles that would be known as the Outer Rim War, culminating in the liberation of the Clavius System by US Imperial forces, along with near-total destruction of the Arm and the death of its leader, Commander Soren, at the hands of then-Lieutenant Alex Corde on the planet Atlas.
The Arm of Orion briefly returned during the Spear Crisis, its captured second-in-command Thorne being freed by Orion's Spear forces and given command of all remaining Arm troops in a large base on the planet Boreas. However, this base base was used as mere bait to lure a USIF task force into an ambush set by the Spear. Though the USIF task force was unaware of the Spear presence, it managed to withdraw to a hidden base on the planet Prometheus.
The remaining Arm forces were incorporated into new units to supplement the Spear in their unsuccessful assault on Prometheus, being forced to retreat to hidden facilities on New Madrid due to fierce USIF resistance.
Together with their Spear superiors, Arm forces tried to carry out plans that threatened to kill millions of innocent lives on New Madrid. Fortunately, these insidious plans were thwarted by USIF troops, with all Arm of Orion remnants finally being wiped out alongside their Orion's Spear superiors during the last battle of the Spear Crisis.