Third Battle of Elysia

The Third Battle Elysia was a major engagement of the Forefather War and one of the largest single battles that took place during the conflict. The third and final major battle to take place on and around the planet of Elysia, it was arguably the single most damaging event to take place on the planet.
==Background==
As the Forefather War neared it's sixth year of active conflict, the Galactic Alliance found itself facing a mounting series of major setbacks and defeats at the hands of the S'southi, their terrifying extra-galactic foe. Three years prior the S'southi had cut like a scythe through the Outer Colonies and launched a series of attacks against humanity's core worlds in the Inner Colonies. Many planets in the Outer Colonies survived untouched, such as Elysia, and were quickly repurposed into heavily fortified fortress worlds as many of the Inner Colonies were.
A combined effort by all races and organisations within the Galactic Alliance lead to Elysia becoming a citadel amongst the now-desolate Outer Colonies from which the GA conducted operations against the rear of the S'southi Armada's advance. The S'southi were getting dangerously close to humanity and therefore the Galactic Alliance's administrative centers and all polities agreed that something had to be done - the S'southi had to be stalled. Cobadarama, at the time one of the chief leaders of the Galactic Alliance's combined navy and the head of the Krythenan Military Council, devised a plan to inflict heavy casualties on the S'southi by utilising the planet of Elysia, which had already been heavily fortified. In addition, Elysia had a comparatively low population of just over one million compared to many of the other surviving outer colonies, meaning that civilian casualties in a hypothetical engagement on the planet would be far lower.
With his plan approved by the GA's war council, a fleet of just over eight hundred vessels was amassed in the system and over two million land forces were relocated to the planet in preparation. The S'southi caught on to the massed troop movements and immediately moved to counter them, with the vanguard of the S'southi armada withdrawing from the Inner Colonies to deal with the force amassing on their flank. 
==Engagement==
===Arrival of the S'southi Armada===
The forward force of the S'southi Armada arrived on the 7th of January, 2566. It immediately began to be assaulted by long-range orbital defense platforms forcing them to go on the offensive. Initially, the S'southi saw very little success; the first-arrivals were not sufficient to break through the defensive perimeter established by the Galactic Alliance's fleet. After several hours, the remainder of the armada arrived and begun to attack the perimeter. 
While the platforms were able to hold for quite some time, they inevitably fell as the battle progressed into the planet's atmosphere. The first S'southi forces made landfall in the Gallia region of Elysia where they were immediately engaged in brutal fighting with a large contingent of the UNSC Army. While the S'southi generally had an advantage in naval engagements due to their vessels being superior in terms of sheer firepower, their ships were not able to conduct the complex manuevers they were known for within atmosphere. This gave their foes a fighting chance and evened the playing field, with the battle now being decided by tactical competency rather than strength. Fighting in the Gallia region intensified significantly as the week wore on, and by the 9th the Divine Covenant had launched a full-scale invasion of the city of Lutetia. 
While unsuccessful at first, the Divine Covenant was eventually able to capture several areas across the city which were suitable for the deployment of S'southi reinforcements, with the battle deepening and intense urban combat delivering heavy casualties to both sides. Slowly the battle began to turn in their favour and the UNSC, out of desperation, quickly organised a fireteam to turn the tide through Operation: BLESSINGS BE
====Operation: BLESSINGS BE====
On the 13th, the fireteam lead by the Spartan-II supersoldier Abelone-777 boarded the Clerical Duty, a CCS-class battlecruiser, and disabled the ship's defense systems through use of Lutetia's Smart AI Athena. With the vessel's weaponry now offline, it was unable to defend itself and was quickly overwhelmed by marine platoons deployed to the vessel's hangars. The Divine Covenant forces aboard were soundly defeated, and the ship now fell completely under their control. The S'southi were unaware of the capture of the Clerical Duty as it's communications had been severed, and therefore did not make an effort to attack the ship or recapture it. The warhead from a DEITY-class missile was transported aboard, one of the most powerful singular pieces of ordnance in the GA's arsenal. After evacuating the rest of the UNSC forces aboard the ship, the Clerical Duty began to return to the Divine Covenant's fleet situated high in the atmosphere above Lutetia, which had been constantly swarming the city with reinforcements and harassing GA positions; once the ship had arrived the warhead was detonated by Athena. The ship and the entire Divine Covenant fleet above Lutetia was wiped out, instantly turning the tide of the battle as the steady reinforcement stream that had kept the S'southi effort in the city afloat was cut off. 
===Lutetia Counteroffensive===
The Lutetia Counteroffensive began on the 14th, a day after the success of Operation: BLESSINGS BE. Through a series of assaults throughout the Lutetia and Gallia regions, the S'southi lost significant swaths of territory and were driven back on every front. In the city of Lutetia in particular, a series of assaults through the city's north-western outskirts saw the Divine Covenant's forces in the city encircled and gradually whittled down as they tenaciously held their ground. The fighting was heavy and the losses on both sides were heavier, but eventually the situation for the S'southi in the city had devolved to such a point where a full scale retreat was ordered, though executed unsuccessfully owing to the Galactic Alliance's aerial superiority over the region. 
In Gallia, key areas of the glasslands were recaptured by gigantic combined-arms assaults, with countless armoured and aerial vehicles supplementing the advance of the main fighting force of the UNSC Army. Sangheili specialists had been conducting guerilla warfare behind the S'southi lines and eventually joined the UNSC's advance when the fighting had reached their location. Tens of thousands of militiamen belonging to the Elysian Militia harassed their foes during their attempts to reinforce their lines, resulting in the S'southi being able to effectively regroup and therefore their ground forces began to crumble. 
By evening on the 19th, the counteroffensive had concluded with the last pockets of organised S'southi resistance in Gallia being wiped out. Regardless, the battle was far from over and the majority of the S'southi's ground forces had not yet been deployed. 
=== Total War ===
The S'southi were eventually able to gain the upper hand in the engagements taking place in orbit and in the upper atmosphere, allowing them to focus more of their vessels on the deployment of ground forces to supplement their failing war effort on the land. A second, albeit unsuccessful, series of attacks on Lutetia took place, and the city of Carpentaria was directly attacked by a large number of S'southi warriors. Carpentaria quickly devolved into little more than an urban battleground, with the city's streets being covered in rubble and the air being blanketed with thick smoke. Alongside their attacks on the major urban centers of Elysia, the deployment of forces into the uninhabitable glasslands of Corail allowed them to gain a foothold on the planet's surface yet again and establish a major landing zone for further reinforcements. UNSC forces suffered a series of setbacks in their attempts to hold areas within Corail, and eventually were forced to withdraw; ceding the entire region to the S'southi's advance.
In Carpentaria, Thierry Plaza was at risk of being overrun by the S'southi, and due to it's sensitive nature the demolition of the plaza was made a top priority. Unwilling to lose the facility, the Elysian Security Forces conducted their own operation lead by Matthias Jaccoud, successfully repelling the S'southi and temporarily ending the threat to the plaza. Spartan-II Abelone-777 arrived in the city on the 30th and assisted with the ongoing engagements beneath the city within the network of underground highways, her intervention being credited with restoring morale to the badly demoralised troops.
==== Battle of Corail ====
By the 5th of February, it had become apparent that the S'southi were using Corail as the main insertion point for their ground forces. A massed assault by three hundred thousand Galactic Alliance army personnel began lead by Brigadier General Devin Weeks with the aim of either driving the S'southi out of Corail entirely or doing enough damage to their landing facilities to weaken them significantly. Supported by over a hundred Spartan-IV supersoldiers, the engagement primarily took place within the desolate glasslands of the region as the UNSC desperately fought to advance against an increasing number of S'southi forces. Eventually, the advance ground to a halt and the fighting deepened into a stalemate; both sides needed to break this stalemate, and immediately began desperate and risky assaults against eachother. An infiltration team composed of Spartan-IIIs led by the Spartan-II Jai-006 managed to sabotage the S'southi's landing facilities near the ruined city of Coral, ending their reliable flow of reinforcements. After a period of reorganisation, the UNSC launched a second series of attacks which tore through the weakened S'southi line and captured the majority of the Corail region after a brutal series of massive engagements; however despite their efforts the S'southi were able to restore their landing facilities and reinforce, the battle deepening into a stalemate for the second time. High command officially called off the attempts to defeat the S'southi in Corail and opted to dig in and wait for a proper opportunity.
=== Galactic Alliance Setbacks ===
The Galactic Alliance began to see defeats across the board. Successful S'southi invasions in the Gallia and Nouvelle Picardie regions saw vast swaths of land be captured rapidly by the invaders, and a renewed offensive by the S'southi within Corail saw the UNSC be driven back significantly. The still-ongoing engagements in orbit saw the GA begin to falter against the extreme numbers employed by the S'southi. Overall, the tide of the battle was shifting in the S'southi's favour significantly and the Galactic Alliance knew it had to do something drastic in order to prevent a S'southi victory.
Concurrent to the earlier stages of the Third Battle of Elysia was Operation: ASTRA, an operation conducted by the Office of Naval Intelligence. The newly-formed Spartan Team Ultraviolet, consisting of John-117, Theo-783 and Rose-788, was deployed after almost six years of investigations had lead to information being overturned regarding the whereabouts of Offensive Bias, a Forerunner ancilla which the Galactic Alliance hoped would help turn the tide of the conflict. After having been successful; completing their mission and task in full, Ultraviolet was being sent to Earth with the ancilla for study. Instead, the Office of Naval Intelligence had them rerouted to Elysia, believing that Offensive Bias being given control over the GA's fleet would be the only way to obtain victory.
By the time Ultraviolet arrived in the Alpha Galilei system, the Galactic Alliance's fleet was clearly losing the engagement. Offensive Bias was given full strategic command over the fleet, and his ruthless tactical brilliance and organisational genius allowed him to reorganise the fleet and mount a series of successful, hard-hitting counterattacks against the S'southi, rapidly turning the tide of the battle in their favour.