Harvest campaign

The Third Battle of Harvest was an engagement during the Human-Covenant War in which the Covenant attacked Harvest again after the retake of Harvest in the hopes of securing a Forerunner artifact buried under the planet's northern pole.

Background
After the Covenant forces on Harvest led by Field Master Re'gish Wamik discovered a Forerunner structure under the ice, the Prophet of Regret sent Arbiter Ripa 'Moramee to lead the excavation operation and retrieve any significant artifacts. A single ship, the Destroyer, engaged the newly-arrived Covenant warships but was left heavily damaged with its reactor leaking. An ONI Prowler was presumably present in-system to witness the battle, but made no attempt to evacuate any survivors from the Prophecy and jumped out of the system to inform Fleet command instead.

On January 6th, 2531, while in a UNSC staging area in interstellar space, Admiral Preston Cole received a message from Commander Orez of the ONI. Orez informed Cole that the Prophecy had repelled newly arrived Covenant warships in the Epsilon Indi System, and that there were survivors to be rescued. The was chosen by Cole due to it's role as a "support ship" rather than a warship. The Spirit of Fire arrived at the system three days after the Prophecy sent their message.

Space Battle
Upon their arrival, Serina analyzed the Prophecy and reported that the ships nuclear reactor was damaged and was releasing harmful doses of radiation throughout the ship. Serina also guessed that the ONI Prowler that reported the battle to HQ was present at the time but did not make any attempt to stop it. The Spirit of Fire attempted to draw the Covenant away from the Prophecy by using its MAC gun and HAVOK Nuclear Warheads upon enemy craft. While it destroyed a number of dropships, they destroyed only one Covenant warship, as the rest gathered behind the Prophecy to avoid being fired upon.

Fire Team Lima, commanded by Sergeant John Forge, was transported to the ship, but their Pelican was fired on and made a crash landing on the Prophecy. The landing resulted in the death of Chris and forced the survivors to do a "soft seal entrance", using torches to burn their way into the Prophecy. They then took part in zero-G combat with Kig-Yar Rangers, easily dispatching them and losing no forces. The team split up with Lima-One (Forge) heading for the NAV room and the rest of Lima searching for survivors. Serina noted to Forge through his visor that the ships AI "FitzGibbon" may act "peculiar" due to elevated radiation levels. Forge was originally denied access to the NAV room by FitzGibbon due to misconduct in his service record. After Forge reminded him of the Covenant boarders, FitzGibbon gladly allowed him entrance into the NAV room to purge the data. FitzGibbon then activated a three-minute self-destruct timer and informed Forge his team was in Bay 2. Upon his arrival at Bay 2, the team quickly evacuated with at least two of the Prophecy's crew. After arriving back on the Spirit, the survivors were taken to the Medical Bay, where Serina informed Forge that the radiation poisoning that the crew sustained was too severe and that they would certainly die.

After the threat in space was destroyed, the ONI kidnapped a civilian scientist, Ellen Anders shortly after a seminar on intelligent life that once existed on the planets Cote D'Azure, Bliss and Onyx. ONI wanted her to decipher a Covenant message written in Forerunner symbols. Anders was then sent to the Spirit of Fire via the. Upon her investigation, she concluded that the message meant that "treasure" (Relics) were to be found, but hidden (from the Humans). Shorty thereafter, Anders scanned the northern polar region of Harvest, concluding that there was a structure under the ice.

Ground Battle
The Spirit of Fire sent UNSC reinforcements to retake the UNSC Alpha Base on the northern polar region near the structure. The base was used as a staging base for Sergeant Forge's reconnaissance patrol, but was destroyed and its occupants routed by a Covenant attack. Forge managed to collect survivors, including Tango 14 and Tango 33, and recaptured the area, destroying the Covenant presence with assistance from Shortsword bombers, and reestablishing the base, from which he lead an assault to capture a Forerunner relic uncovered by the Covenant. During the battle, the Pelican Bravo 29 delivered reinforcements to a landing pad from the Spirit of Fire. As the UNSC forces approached the Forerunner relic, the Prophet of Regret ordered the Arbiter to destroy the structure in order to prevent it from falling into enemy hands. However, the UNSC managed to destroy the detonator in time, and push into the interior of the structure.

Upon capturing the structure, Anders opened up a holographic map of nearby star systems. Several Sangheili disengaged their Active Camouflage and attacked Forge's group. When he and his Marines were pinned down, Alpha Base sent reinforcements, but arrived too late to rescue them. Two Grizzlies were dropped in from the Spirit of Fire to help Forge escape. The Grizzlies arrived in time to save Forge and his men, along with the professor. The company then tried to leave over the energy bridge that the Grizzlies came over, but Grunts destroyed it. Anders then repaired the second, already disabled bridge, which the company then crossed and are then forced to fight through Covenant reinforcements. The Grizzly tanks cleared a path and led Forge and Professor Anders to waiting Pelican dropships to return to the Spirit of Fire, while the Alpha Base reinforcements Marines held off the Covenant.

Aftermath
The information gained by the Covenant from the Forerunner structure led them to the UNSC colony Arcadia. Anders was drawn to the same planet after examining the artifact. The Covenant attacked Arcadia on February 9th, 2531, closely followed by the Spirit of Fire.