Battle for Arcadia

The First Battle of Arcadia was an engagement fought between the United Nations Space Command and the Covenant on the Human colony world of Arcadia during the early parts of the Human-Covenant War in 2531.

The Battle
Shortly after the Third Battle of Harvest, the Arbiter and his ships quickly left the system after learning the location of Arcadia from a Forerunner artifact buried under Harvest's north pole. Under the suggestion of Professor Ellen Anders and Permission from Admiral Cole, the followed in hot pursuit.

Upon reaching Arcadia, two Covenant vessels exited Slipspace. The Spirit of Fire arrived soon after. The UNSC Belfast, Texas, Pillar of Autumn, and Armstrong engaged the two ships immediately, catching one of them with its shields down and destroying it. However, the UNSC force suffered its part of the battle. The Texas and Belfast were destroyed, the Armstrong was venting atmosphere due to damage, and the Autumn suffered severe damage.

Ground Battle
The second Covenant vessel was engaged in "surface activity" on Arcadia, attacking Civilian targets and Pirth City, Arcadia's capital. The Arcadian Patrol, the primary police force of Arcadia, was deployed to counter the Covenant invaders but, being a civilian force, was easily overwhelmed. SPARTAN Red Team and forces under the command of Sergeant John Forge assisted in rescuing civilians, evacuating hundreds to several civilian transports abandoning the city. The Covenant, unfortunately were successfully in destroying several of these transports, resulting massive civilian casualties. However, despite several repeated assaults, the UNSC was successful in saving at least a portion of the population before being forced to retreat to the city's outskirts, where they were reinforced by SPARTAN Team Omega. Forge's team fortified the outskirts and linked up with several groups of stragglers. These forces, led by the SPARTANs, teamed up to destroy a Covenant field base, from which the UNSC survivors suffered several assaults.

Following this, the UNSC forces established a base of operations at a deserted ONI base in the jungle. They used experimental Rhinoes to break through a massive dome-shaped Covenant energy barrier concealing a Scarab building site, as well as several Forerunner ruins. The UNSC forces were constantly harassed by Covenant air patrols, but were successful in repelling them. After the shield dome was disabled, the UNSC advanced on the Scarab's construction site, taking cover behind the Forerunner ruins as the Scarab fired on them. After a considerable effort on the part of the UNSC, they destroyed the Scarab and proceeded to investigate the site.

Aftermath
Despite the victory, the UNSC suffered a major setback as it investigated the Forerunner ruins on Arcadia. Under orders from the Prophet of Regret, the Arbiter traveled back to Arcadia and captured Ellen Anders, with the intention of using her to activate The Apex. The Spirit of Fire chased his ship to the Shield World, unable to alert the UNSC of their target destination.

The UNSC regained control of the planet, but now that its location was known to the Covenant, most of its inhabitants abandoned the colony. A small number remained, establishing the settlement of Abaskun on the Mu continent, which supplied the UNSC with much-needed foodstuffs until the colony was destroyed in 2549, when the Covenant returned.

Trivia

 * Some of the footage of cameras viewing the battle aboard the Spirit of Fire used for the cutscene was part of the Five Long Years Cinematic trailer.