Despite their major numerical and technological advantages over humanity, by 2531, the Covenant High Prophets had realized that the task of destroying an entire sapient species had a logistical burden beyond anything that the Covenant military could muster without leaving Covenant space defenseless. Despite the UNSC's disadvantages, the Prophets considered the UNSC's armed forces powerful enough to pose a threat to the Covenant. These concerns would be justified by extreme Covenant losses during the war's culmination in 2552. The Prophet of Regret dispatched an Arbiter to Harvest to claim a Forerunner artifact buried under the north pole of Harvest. Acquisition of advanced technology would allow a quick, decisive victory in the conflict.
Preston Cole counter-attacked by sending a force composed of UNSC Spirit of Fire and UNSC Prophecy back to Harvest after receiving a message from an ONI Prowler. The battle resulted in victory for Cole, despite major casualties. Upon discovering that the Covenant, under the command of 'Moramee, had excavated Forerunner artifacts in the northern polar region, Captain James Cutter deployed ground forces to remove the Covenant occupation. After a heated fight on the planet's surface, the UNSC forces were able to examine the artifact, a star map, and realized in horror that information had led the Covenant to another UEG colony: Arcadia.
As predicted, the Covenant followed the information from the artifact to Arcadia. The Covenant hoped that the planet would contain more Forerunner artifacts for them to claim, and while they only found a complex of ruins, information garnered from them led them to Shield 0459. Spirit of Fire followed and removed the Covenant presence from the planet. However, 'Moramee's capture of an important civilian researcher forced Captain Cutter to pursue the Covenant without reinforcements.
On the Shield World, the crew of Spirit of Fire eventually discovered that the Covenant needed Professor Anders, by definition a Reclaimer, to activate the Apex and claim the huge fleet of Forerunner starships within. A group of Marines, together with Spartan-II Red Team, rescued the researcher and destroyed the Shield World. The Arbiter was also killed by John Forge during the battle, though the Prophet of Regret escaped.