Battle of Second Sanctum

The Battle of Second Sanctum, also known as Operation: MOBY DICK, was a raid carried out by UNSC forces following the disastrous against a moon-based Covenant fortress known as Second Sanctum. This was not an officially-sanctioned military operation, and was instead an act of retribution against the Covenant for their actions on Reach with the intent of causing as much damage as possible.

The operation itself had been planned over a month beforehand after strategists working with the had pinpointed Second Sanctum's location via a  attached to a Covenant vessel earlier that year, though the sudden invasion of Reach had led to its cancellation. As the only individual with knowledge of the operation to escape the planet, Captain Jeanette Nisha chose to gather a force large enough to attack the Covenant base after discovering that their foe was transferring Human prisoners there for some unknown purpose.

Following weeks of preparation, which included the first-ever capture of a and its crew and the surprise arrival of a Spartan team, an attack force was dispatched to Second Sanctum with the intention of infiltrating the heavily-guarded facility and destroying it. While initially successful in their endeavour, the ground force was eventually discovered and a lengthy battle ensued as UNSC forces engaged in guerrilla warfare around Second Sanctum for hours, throwing the surprised Covenant into disarray. As Covenant forces stationed at Second Sanctum dispatched an entire against the invaders, Battlegroup Cossack launched a surprise assault that tied up the station's defence fleet and allowed for reinforcements to land on the moon's surface to join their comrades. The Spartans would lead a successful attack into Second Sanctum's prison area, freeing those held captive while other special forces personnel broke into the fortress to set up explosive devices that would destroy the structure.

While they were heavily outnumbered, UNSC forces on the ground were able to inflict major casualties on the Covenant defenders and managed to keep them at bay long enough for their infiltration team to blow up Second Sanctum's command centre. It was at this point that the Fifth Fleet of Furious Consequence arrived in-system, blindsiding and destroying half of the attacking UNSC Fleet in a single volley of plasma torpedoes that sent the others fleeing for cover around the other side of the moon. This lapse in air cover allowed the Covenant to land thousands of fresh troops on the planet's surface, overwhelming most of the UNSC attackers and prompting a swift retreat.

Left with few options, the surviving ships of Battle Group Cossack launched a desperate operation to retrieve their stranded comrades, sending in a wave of dropships to extract the survivors from the moon's surface before ordering an immediate retreat. While Longsword cover helped fend off Covenant air attacks, most of the attack force were wiped out in hours; the UNSC Bright New Day was the only ship to be completely successful in rescuing its crew and escaping. In a final act of defiance, the Prowler Theseus launched its payload of nuclear missiles into what remained of Second Sanctum, utterly vaporising the area before it was torn to pieces by Covenant vessels.

Of the force that attacked Second Sanctum, only the Bright New Day and a single Halberd-class Destroyer - Illustrious returned to the rendezvous point, carrying less than 10% of their initial complement. Despite their losses, the survivors had rescued a number of POW's from captivity and destroyed what they assumed was a fairly important Covenant military base in the process, which counted as a victory of sorts after the tragedy of Reach. The survivors would go their separate ways afterwards, and upon returning to the Bright New Days Spartans would relay the events of the battle and its participants to HIGHCOM, ensuring that their sacrifices would be remembered.

Prelude
As fell to the Covenant, a unit the Office of Naval Intelligence's  force, Oscar-Nine, and the  ensured that nothing valuable would be left within their various facilities for the Covenant to find and discover, placing Captain Jeanette Nisha in charge of this operation while various highly-ranked personnel evacuated to safer systems. In addition to astronavigation data and files that might give their foe information on any surviving Human colonies were a series of reports pertaining to Covenant bases that fell into Nisha's hands. While most were deleted, the Captain kept a file that she herself had spent months compiling regarding a Covenant fortress that intercepted communications had learned was called 'Second Sanctum'.

Seeing the widespread death and destruction on Reach and what looked like mankind's darkest hour, Nisha ordered all ONI personnel under her command to withdraw and flee the system. She would lead several ships away aboard a Sahara-class Prowler, the UNSC Theseus, heading towards a barely-charted system that acted as a rally point for several fleets. While Reach's fall would normally prompt an immediate fallback towards the to await further orders from ONI, Captain Nisha would spend well over a week moving between UNSC rally points in search of other ships that had survived Reach. By mid-September, they had gathered seven other ships and discovered the UNSC Cossack, a critically-damaged Marathon-class Cruiser that was eventually stripped for equipment after the deaths of most of its crew and the failure of its engines were confirmed. Finding herself in charge of a small but potentially effective fighting force, Nisha deliberately chose not to deliver the ships towards Earth and formed 'Battle Group Cossack' after fabricating orders, supposedly from HIGHCOM, that they were to launch a counter-attack against Second Sanctum as soon as possible.

While most of those spread out among the crews did not like the idea of attacking the Covenant, none dared disobey an order from an ONI Captain and the Battle Group began to prepare itself for the assault. While Nisha came close to cancelling the operation as the shock of Reach's fall wore off, enemy communications intercepted by the Theseus revealed that Covenant vessels heading towards Second Sanctum were coming straight from the battlefield with a particularly strange cargo: Human prisoners. The prowler's crew soon found out through further transmissions that experiments of some sort were being carried out there, which only served to anger the gathered forces. Resolving to destroy Second Sanctum, Battle Group Cossack moved towards a system where they surprised a small group of Covenant salvage ships picking over the glassed planet Harpa. Working under Commander Erwin Durant, the ONI Security force managed to board an after it landed and took some of its crew prisoner, forcing its  pilots to take them to safety.

Another week was spent interrogating the prisoners before several Unggoy, who had been treated poorly by the Covenant, offered to assist the Humans by flying the newly-acquired Lich towards Second Sanctum, where it had been based from. While the vessel could not enter slipspace under its own power, the alien prisoners revealed that a salvaging vessel was scheduled to pick them up from Harpa on October 14th and return them to the base with any recovered items, giving them a perfect chance to sneak in-system undetected. While distrustful of the aliens, Nisha and her forces had little choice and agreed to give the compliant Unggoy their freedom if the attack went well. On October 12th, shortly before they were to return the Lich to Harpa, a single Paris-class heavy corvette arrived at the Battle Group's rendezvous point, heavily-scarred but otherwise perfectly functional.

To the surprise of all, the ship was led not by a Naval officer, but by a team of SPARTAN supersoldiers and a depleted squad of Orbital Drop Shock Troopers who had not only escaped Reach, but two more engagements afterwards. As with the rest of her subordinates, Nisha informed their leader, Master Chief Petty Officer Kane-099, about their supposed task from HIGHCOM. While the SPARTAN-II seemed suspicious of the ONI Captain, he agreed to assist Battle Group Cossack in the attack. On the eve of battle, Nisha christened the mission as 'Operation: MOBY DICK' and had three of the Spartans join Commander Durant and most of Oscar-Nine as part of the infiltration group while the remainder of their groundside forces stood by to act as reinforcements when the attack began in earnest. Standing by with its stealth systems activated, the Theseus watched as the captured Lich was escorted into slipspace by the salvaging ship, and prepared to signal the rest of Battle Group Cossack to attack Second Sanctum.