"If you see one of those things in the skies of your colony, you can say goodbye to your rebellion. Those damned carriers are in it for the long haul."
The Orion-class assault carrier (hull classification symbol: CVA) is a purpose-built planetary assault vessel that is utilised by the UNSC Navy. Introduced during the formative years of the Insurrection, the Orion-class is built to fulfil the critical issue of supporting massive peacekeeping campaigns that would later become characteristic of the conflict. It is considered poorly armoured compared to carriers which came after it, and armed well enough to only fend off a moderate attack. However, its vast internal factories, the same type utilised on some models of colony ships, and hoards of armoured ground units sees them having no equal when performing planetary invasions.
The first Orion-class assault carrier were first deployed within the first five years of the civil war. Mass-produced to support offensive operations against the badly-coordinated "bushfire wars" that would make up the early Insurrection, their success during this crucial early period would see the Orion-class become a harbinger for the UNSC's inevitable victory. Unfortunately, the beginning of the Human-Covenant War would see these carriers taking atrocious losses during the war. With little in the way of defences and many ground battles ending once space superiority was lost, as well as the class being spread throughout the Outer Colonies, the Orion took the highest number of casualties compared to any other capital ship during those first five years of war. Few carriers which escaped this fate would be either pulled back into the Inner Colonies to support sustained sieges, or used to form the core of expeditionary fleets to attack Covenant logistic sites.
Only a handful of Orion-class carriers would survive the war, mostly those relegated to support manufacturing bases to replace much of the material lost at several 'last stands'. As the largest class of factory-ships available to the UNSC, they were retasked with recolonising planets whose biospheres were still habitable and locating lost human colonies, and with many being reassigned under the newly-formed UNSC Frontier Command. However, whenever destroyed through sabotage, battle, or simple decommissioning, no Orion-class carrier would survive past the Created crisis.