Third Sphere Expansion - Second Agrellan Campaign: Following the great victory upon Prefectia, Ethereal Supreme Aun'Va gave an impassioned speech. It was an awe-inspiring sight, the Ethereal hovering over the crater-ridden battlefield, the burnt-out frame of a fallen Imperial Knight as his backdrop. It was a broadcast viewed by every member of the T'au race, even those too young to walk.In his victory speech, Aun'Va announced another T'au triumph. He praised the leadership of Commander Shadowsun, and acknowledged the mastery of the Fire Caste. The Ethereal Supreme spoke of how the T'au race stood now on the precipice of greatness. Before them lay endless possibilities -- they had but to seize them.Once, the Damocles Gulf had thwarted their expansion, as had the rule of the Imperium of Mankind. The T'au had now overcome these obstacles to stand once again victorious.Aun'Va announced that the Third Sphere Expansion was only just beginning, and called upon each Sept World by name to give more of themselves to the Greater Good.Just as the frontline soldiers of the Fire Caste were asked to give everything in defence of the Tau'va, so too must each citizen of the T'au Empire; production must double, new technology must be developed and every part of society must be made more efficient.It was a staggering statement, for the T'au Empire was already on a war footing -- production was running at maximum capacity simply to supply the enormous amounts of materiel needed to fund the Third Sphere Expansion. Yet Aun'Va  was asking for more.To this request, the T'au responded with earnest devotion. If the great leader of their people asked, it would be done. There would be no questions and no qualms about the cost, only ardent efforts to increase production by any means necessary.With the foe gone from Prefectia, Aun'Va began to plan the next phase of the expansion. Half of the Fire Caste forces on Prefectia were sent to aid in the exploitation of the Dovar System -- suppressing or eradicating native populations, protecting Earth Caste installations and safeguarding Water Caste diplomatic actions.The remaining forces were to return to Mu'gulath Bay. There, they could briefly refit and train while the war council laid plans for the next wave of planetary invasions. It was generally accepted that the Imperial hold upon the region had been broken, and it would be a long time before their forces returned in great numbers.The Imperium had suffered a series of losses that would have set the T'au Empire back generations, including the latest blow -- losing the "King" of the Space Marines. It would take them some time to recover from such shattering setbacks. In their understanding of the Imperium and its ways, the T'au could not have been more wrong.Even before Agrellan was attacked, the aggressive infiltration of the T'au Water Caste had been marked. Astropathic choirs broadcast warnings and armies were already mobilised before the T'au's lightning fast invasion was complete. The T'au success only increased the magnitude of the Imperial response.That many of the region's lesser holdings had previously given into T'au bribes and manipulations had only increased the Imperium's desire for retribution. Perhaps the only thing the Imperium was less tolerant of than xenos invasion was the betrayal or corruption of its own. The seditious, those who would lure Mankind to their doom, were loathed above all.Forces were mustered, congregating in numbers beyond the scope of what the T'au believed possible. The vast armadas and armies of the Imperium were slow to gather momentum and had to span distances the T'au could not fathom, but once Task Force Retribution was finally launched into the Warp, there was no stopping its single-minded mission to reclaim the territory once ruled in the Emperor's name.The warriors of the Astra Militarum would not halt until they had raised the glorious banner of the Imperial Aquila where it rightfully belonged. And so, when the task force emerged from the Warp with klaxons blaring, it was as close to Agrellan's orbit as they dared, to maximise the advantage of surprise.Soon all wrongs would be revenged a hundredfold.The Second Agrellan Campaign, as Imperial savants would later name it, began well for the Imperium. Task Force Retribution's naval contingent was led by Lord Admiral Hawke while its Astra Militarum elements were commanded by the Cadian Lord General Troskzer from space.With the aid of the Raven Guard, the Imperial Navy successfully claimed the space above Mu'gulath Bay from the T'au orbital stations and fleet. The ground invasion was then led by the forces of the Astra Militarum, the Skitarii Legions and the Legio Cybernetica, screened by elements of the Raven Guard commanded by Kayvaan Shrike and the White Scars again led by Kor'sarro Khan.Troskzer and Shrike deployed their forces at three primary locations on the planet. These three fronts, the central, eastern, and western spearheads, would converge at the largest T'au installation located at the old capital hive city, Agrellan Prime.The ground invasion went well, and though Commander Shadowsun sprung yet another of her traps, the assault proved clumsy and hastily assembled, and it became apparent that the Imperial forces would weather the assault.Then the skies turned red. For Commander Farsight and the forces of the Farsight Enclaves had come to aid their estranged brethren.Shocking all sides, O'Shovah himself appeared on the field, followed by his command team The Eight. They led a great Mont'ka assault on the Imperials. The Imperial commanders realised that with the arrival of the T'au reinforcements, victory had been snatched from their grasp and the world could not be reclaimed. They ordered a withdrawal in force, moving to Blackfossil Ridge amid a heavy supporting bombardment.They were joined by the Space Marines, who were evacuated from the field by Thunderhawk gunships save for the White Scars contingent under Kor'sarro Khan, determined to claim the head of Commander Shadowsun as they had sworn.The tide seemed to turn again when an Officio Assassinorum Execution Force appeared on the battlefield, determined to slay the T'au's most important leaders. As chaos erupted among the T'au forces with the Assassins' attacks, Shadowsun managed to rally the T'au and withstand multiple reinvigorated Imperial assaults.However, while in her mobile command post, Shadowsun was suddenly assaulted by a Callidus Assassin disguised as the Ethereal Aun'Kar. Shadowsun was wounded, but with the aid of a force of Pathfinder bodyguards managed to take down the shapeshifting Imperial operative. But other members of the T'au Empire's critical leadership were not as lucky.The Ethereal Supreme Aun'va, trapped on Mu'gulath Bay at the time of the unexpected Imperial invasion in the wake of his speech heralding the great victory on Prefectia, was attacked by a sinister Culexus Assassin in his hidden bunker in the ruins of the hive city of Agrellan Prime. The Culexus psychically overwhelmed all of Aun'va's bodyguards before successfully hunting down and slaying the Supreme Leader of the T'au Empire.Task Force Retribution had been intended to scour the xenos race known as the T'au from Agrellan, as those who had dared to confront the Imperium must learn of the consequences. That mission had been deemed a failure, and other elements within the task force now took precedence, and the evacuations of the Astra Militarum forces began.The Space Marines that escaped Farsight's ambush had fought their way to evacuation points and returned to their orbiting spacecraft. They were in the process of rearming and coordinating their redeployment when they heard.A new lord general had replaced Lord Troskzer, and his first act had been to issue an order calling for the Astra Militarum's immediate withdrawal from Agrellan. All Chapters looked to Kayvaan Shrike, for the Adeptus Astartes were under no authority but their own, and they wished to see what their highest ranking officer would do.Shrike announced that the Raven Guard would depart within the solar hour. So the Adeptus Astartes quickly embarked for other destinations, as there were more distress calls than Imperial forces to answer. Theirs was the way of war, and the concerns of one campaign or planet mattered little to them. Kor'sarro Khan, however, was enraged.Once again the Khan was denied, once again he had failed to bring back the head of Commander Shadowsun. He was stubborn-minded enough to disregard what others were doing and continue with his own dwindling company of White Scars, but an additional command came.This one originated from the White Scars Chapter Master Jubal Khan. The remnants of the 3rd Company and its support were needed urgently back at Chogoris -- there could be no delays. The Khan was needed to help fight the Traitor Marines of the Red Corsairs.Either not content with their triumph, or not wholly convinced of their foe's retreat, the T'au Empire counterattacked the retreating Astra Militarum and Adeptus Mechanicus forces as they made their way towards designated pick-up points across the planet's surface, often and without mercy.Ambushes slowed the Imperial forces or drained off their strength in hopeless pursuit. Yet worst of all were the air strikes. Imperial atmospheric flyers were concentrated around the landing zones, leaving the retreating masses on the ground open to the T'au Air Caste's endless strafing attacks and bombing runs. Beaten, bedraggled and showing the signs of early-stage rad-sickness, the foot soldiers of the Astra Militarum dragged themselves onwards beneath the blazing sun.In the end, many high-ranking officers of the Imperial Guard were winnowed out from the massed retreat and ferried to the landing zones aboard Valkyries. Those taken were the most highly decorated of their kind. Special operations airlifted out High King Tybalt of House Terryn and his remaining Imperial Knights, who returned to Voltoris for much-needed repairs.In addition to key officers, heavy equipment was given priority. Far away, members of the Departmento Munitorum had rightfully reasoned that it was those items that were far harder to replace than the many millions of men that would soon be abandoned to their fate, though approximately fifty percent of the surviving Astra Militarum ground forces managed to make it off-world before the end came.After disbanding the Task Force Retribution, Lord Admiral Hawke received a special gift from the Adeptus Mechanicus -- a specialised torpedo warhead capable of unleashing a very particular form of Exterminatus upon Agrellan by the unusual gasses present in the atmosphere of its northern hemisphere into a planetary firestorm.The Third Sphere Expansion was over.Mu'gulath Bay burned. The chain reaction sent unnatural firestorms sweeping over the lands of the T'au Sept World. This was beyond the T'au enviro-engines' ability to halt or control. Anything not beneath a protective shield dome was doomed. And only a single shield dome remained -- the massive one that spread over the city that the T'au called Lo'vasht'au. Many millions of T'au died, as did those soldiers of the Astra Militarum left behind by the foe.When the Kor'vattra finally arrived they did not recognise the planet. The news they brought was worse still. Fires did not burn upon Mu'gulath Bay alone; the strange phenomenon known as the Damocles Gulf had become a roiling inferno. Those labyrinthine passageways through the region that it had taken the T'au so long to discover were untenable once again.For many Terran days, those trapped beyond the vast barrier were faced with the unsettling truth that they might never travel back to the Sept Worlds, that they were cut off forever from the T'au Empire. Communications could pass through the barrier, but starships could not.Earth Caste engineers, however, were working ceaselessly to perfect a shield that would protect starcraft from the highly corrosive gases. Early tests were positive, as some ships survived the passage across the Damocles Gulf, but the failure rate was high.Commander Shadowsun had recovered from her wounds, although she still grew weak quickly. As Supreme Commander of the Empire's Fire Caste, she spent long sessions with the Ethereal High Council, for there was much to plan and discuss. Terrible rumours swirled around the T'au Empire, but all fears and doubts were silenced by the announcement that, in a matter of Terran days, Ethereal Supreme Aun'Va would broadcast a speech, his new statement to be beamed across the Sept Worlds and beyond. It was to be a message of hope and courage, a message to be seen by all children of the Greater Good.Commander Farsight was gone from Mu'gulath Bay, returning to exile in his Farsight Enclaves. His exit was sudden and without notice, for he left before the Ethereal High Council reached the inevitable conclusion that he must be captured and tried for treason to the T'au Empire.Shadowsun knew she would be ordered to apprehend Farsight by the Ethereal High Council to force him to undergo a Trial of Judgment, a task she knew that she would carry out reluctantly but loyally. In truth, Shadowsun suggested that Farsight leave the system before those orders were given to provide her former ally a head start in making his escape.Farsight left behind the roiling flames of Mu 'gulath Bay even as the hologram of the dead Ethereal Supreme began its broadcast to the Septs. While his warriors began their dangerous journey home, they listened to Aun'Va's speech. He spoke of the Empire's tragic losses, of how they would make them stronger. He spoke of how, more than ever, enlightenment must conquer savage barbarism. Aun'Va's image spoke of never underestimating their foe again.It was only near T'lasla -- a planet earmarked for future T'au colonisation -- that the Enclaves fleet had received the distress call. In response, Farsight deployed his forces to the aid of T'lasla -- and the defeat of the Tyranid hordes of Hive Fleet Leviathan.