15,000 meters, good visibility, this was the sweet spot, the altitude where the air resistance gave way, and a craft seemed to just float through the sky. There was an intermittent wind from the north-west that would extend flight time by a few minutes. Kor'La Zro gazed out through his cockpits 360-degree camera view. The desert stretched out below him, almost as far as the eye could see. It was only in the very north that he could make out the beginnings of a mountain range. The Peaks of Heaven if he remembered the conversation with one of the Human auxiliaries correctly. 5000 meters below him schools of Remora Drones flited above the landscape, searching for the elusive enemy. They were out there, somewhere….
"Three you're drifting!" barked the voice of Kor,UI Zole, the leader of the eight craft formation. Zro felt his adrenaline spike as he frantically cast his eyes over the instrumentation display. He was drifting, by three meters. He acknowledged and corrected, a pang of irritation rising inside him. Kor,Ui Zole had never been an easy superior to work with, always demanding the best from the young Kor,La under his command. In the 13 days since the attack on the airbase, he had become unbearable. Snapping at any who seemed to not live up to his standards, which seemed to be everyone he came across. The other day Zro had seen him ranting at a pair of Earth Caste technicians because the fuel bowsers being used to surface the squadrons machines had apparently been parked too close to the vehicles, violating some obscure guideline that Zro had never heard of. How the Earth Caste were meant to avoid that when their home airbase had had its total complement of machines doubled almost overnight, he had no idea.
Things had been hectic since the attack on airbase Anor'the. The Fire cast had moved fast. Rounding up human tribes and relocating them to hastily built camps. There had been violence. Many of the Humans had been assured that they could live on their own lands for as long as they wanted. Now the Tau seemed to be breaking that promise. Most of the resistance was symbolic, chanting and hurling insults before the Elders of the tribe managed to get control over there people. From conversations with some of the Shas La on base, a small but significant number of Human tribes had reacted much more violently. News of the resulting one-sided slaughter seemed to have spread unnaturally fast because a noticeable number of Humans had simply disappeared. Their villages abandoned overnight.
Now the Fire cast had declared the relocation compleat. Squadrons of Tau drones were patrolling, searching for the unknown enemy. Above them, flights of Baracuda's fighters, Tiger Shark bombers and Orca transports patroled. Ready to swoop down on the enemy once they were located. The orders were clear. The relocation of the Humans was complete. Anyone detected by the Drones outside of the settlements was fair game. Zro wasn't too sure about that but he supposed it made sense. The Humans had been offered the greater good and had chosen to reject it. What had to be done was unpleasant but necessary.
The eight Tau Barracuda fighters were flying in two, four machine formations. Arranged into the shape of a diamond. The formation that most species with experience of air combat gravitated towards after a certain amount of combat experience. Naturally, Zro's partner in his part of the formation would have to be Kor,Ui Zole.
Zole called out a course correction and the flight's machines responded accordingly. Zro glanced around his canopy's camera display. More because he was bored than because he expected to notice anything important. After all his scope was clear and there was nothing on the communication channels.
Which was when he saw them. Four black and crimson machines diving down on them. They were menacing things, with swept forward wings that ended in vicious points. They were coming so steep and fast that it would break apart a Baracuda.
This wasn't happening. This couldn't be happening. This was how it happened in dreams, in nightmares. He was so shocked that his warning was almost too late.
"Break! Break! Bandits above!" He threw his machine to the right and fired his vector thrust at maximum, eating into his fuel reserves. He felt his gravity armour struggling to prevent the G forces from pulping his relatively thin and frail Air cast body.
The Tau formation descended into chaos. From his four-plane formation, Zole was the only other pilot to react quick enough. The other two members of the formation were ripped apart as the unknown fighters fired some kind of nose mounted twin linked particle cannon. Their machines were literally split in half as they flew into the streams. The two halves splitting apart from each other and falling away before internal explosions atomised them.
The other flight suffered less. It lost its leader who's machine suffered a containment break of its Ion cannon's fuel cells, but the remaining three machines speed through the blizzard of fire from the two enemy machines attacking them unscathed.
Chaos erupted on the communications net. He could hear Zole screaming at them, cursing them for fools, for neglecting their visual scanning, for allowing them to be bounced. He wanted to scream that it wasn't their fault. That their sensors should have warned them what was coming, and that Zole and been flight and section leader. That he was as much to blame as the rest of them. But he didn't. partially because he suspected it would only add to the confusion and mostly because he was trying to not die.
One of the bandits was on him. They were in a turning fight. And he was losing. That shouldn't be happening. The unknown attacker had dived down on them, hadn't it? Logic dictated it would have too much speed to stay behind his machine, it would overshoot him as he turned and then he could riddle it with fire. Except as soon as he had hit his airbrakes and heard his crafts antigravity systems low murmur raise to a high-pitched whining the enemy machine had matched speed with him. Even worse it was turning slightly harder than he was.
His fingers danced over the joystick, arming his eight wing-mounted missiles and the two wing mounted drone controlled burst cannons. The burst cannons swung backwards to face his rear. "That's right you little Castles1 one, get closer!" he snarled."
"Target not found." His weapons system informed him in infuriatingly calm tones.
"What? It's right fucking there!" Frantically he overloaded the system and manually triggered the weapons. The enemy machine flew straight into the twin streams of blue plasma fire. Zro let out a cry of satisfaction only to stare in disbelief as the unknown machine emerged from the resulting cloud of superheated air seemingly untouched. The image of it filled his camera screens. He found his eyes drawn to the twin cannons jutting out from under where the cockpit must surely have been. Fear gripped him.
Kor,Ui Zole tore in from 3'oclock and below the enemy machine with one engine disabled and all weapons firing. Unable to acquire a missile lock for the burst cannons he had slaved them to his ion cannons targeting system, unlike Zro he had also launched his missiles. The enemy fighter flew straight into the maelstrom of fire. For a moment it seemed to hang in space and time completely untouched. Then the crimson and black armour tour itself apart, its death was so violent that there seemed to almost be a force inside the machine doing the bulk of the destruction. As though whatever technologies gave it flight and such durability were finally rebelling against it.
"Are you alright Kor'La?"
"I, I think so. Sir your engine!"
"It's fine. Got peppered with fragments when those, things took out one of ours."
He glanced at his display. The 3D display was still obstinately free of enemy contacts. Showing only the Tau machines twisting and corkscrewing through the air. Of the eight that had started the battle three had been destroyed instantly. Another had been destroyed soon after resulting in the fragments that had damaged Zole's machine. That left just four machines, scattered and in the case of one of them damaged against three enemies of unknown capabilities. He could see the enemy machines. They were gunning in hard on the survivors of the other Flight. One of the Tau pilots panicked and in an attempt to climb and allow his enemy to undershoot him stalled his craft. The enemy machine, displaying a reaction time that put any Air cast pilot Zro had met to shame copied the manoeuvre, demonstrating the same unnerving ability to change velocity rapidly that had nearly killed Zro it stood in its tail and pulled up, firing its weapons as it did so. The unfortunate Tau pilot was blasted apart before he could cry for assistance.
Regrettably, for the unknown enemy, his manoeuvre had left him in a perfect position for Zro to sweep in and rake the enemy machine with a three seconds blast from the Ion cannon. His heads-up display screamed a warning about weapon temperature. Instinctively he dumped his weapon coolant. That cooled the weapon enough to fire but gave him only a second of sustained fire.
A garbled scream came over the communication network Another Tau machine fell burning from the sky. Its pilot was trapped in its cockpit. There were flames in the cockpit. Zro breathed a sigh of relief when Zole used the command override and shut off the communications channel.
Now it was two against two. Both sides formed up. Zole's machine was sluggish with only a single engine but his response to Zro's suggestion that he should disengage was filled with enough expletives to make Zro laugh despite the rising tension as the four machines tore towards each other.
His missiles still obstinately refused to acquire a target lock. His drone controlled pulse cannons were no good either. Snarling a curse that he was not sure was directed at the Earth cast technicians who maintained his machine or the enemy. Instead, he slaved them to his Ion cannons aiming system and called up the holographic sights. The distance between the two groups of aircraft rapidly dwindled.
"When I give the word. Hit you vector thrust. You go high, I go low." Said Kor,Ui Zole
A heartbeat later. "Now!"
Zro poured every last iota of manoeuvring fuel he had left into the manoeuvre. This was what the Fire cast referred to as the killing blow he was sure. The single pivotal moment that would decide the battle. Zole shot was of course perfect. His target wasted its volley by raking empty air whilst burst cannon and ion cannon shots overwhelmed whatever technology gave them their remarkable durability. Zro's fire was less successful. It splashed across the enemy machines right wing but failed to inflict significant enough damage to destroy it. The enemy machine banked to the right and started to line itself up on Zole's machine, which because of the damage to its engine was struggling to stay airborne. Its sole surviving engine was starting to misfire.
Zro cursed and tried to line up a shot. The crosiers fell across the enemy machine and he triggered his Ion cannon. Nothing happened. The last burst from his Ion cannon had turned some component of his main weapon into slag. He fell in behind the enemy machine and using manual aim strafed it with his burst cannon. The enemy machine displayed the same infuriating durability that its fellows had also possessed. Seemingly ignorant of the volley of burst cannon fire striking its engine housing it fired its weapons. Zole displayed his skill at piloting by triggering his vector trust at the last possible moment. Instead of obliterating his machines engine compartment, the burst of particle cannon fire from the enemy machine merely erased his left wing. As his machine spiralled out of control Zole punched out, his cockpit detached, firing its thrusters to clear itself from the enemy machine and activating its parachute.
One on one thought Zro as he tried to stay on the enemy's tail as it began to turn to attack him. Once again it simply seemed to be able to turn at a rate that was impossible to for his machine to replicate. His burst cannons ceased fire, their ammunition expended and their barrels heated to the point of turning to slag.
Then something happened. The machine ceased its turning. As its path straightened out and it continued on a straight path Zro pulled up behind it. He activated his air to air missiles and then set them to manual fire, a tactic only used when engaging ground vehicles. He centred his crosshairs on the enemy machine. Then the unknown machine exploded.
/
"What happened?" asked Cro'ps as the last icon donating the four strong flight of Prowler fighters disappeared from the tactical display.
"It means that "something" is "fucking" with the Quantum Realm, weakening our signal to such a point that the automatic safeties in our units believed that the Commander of our forces has been killed and his units must execute self-destruct protocols to protect themselves from capture by the enemy. It means that we can't just bury our enemies in tidal waves of unmanned tanks and aircraft. Not without a human in a war machine nearby to provide a Quantum Signature to prevent the self-destruct protocols from activating."
"Can't you override that, your tribe seems to give its members a lot of autonomy."
"No I can't fucking override it. For the same reason that I can't walk on water, without augments at least. It's so hard-wired into every file of our units programming. Damit. I was sure our modifications would work." I drummed my fingers on the desk. Cro'ps was the only person present physically but there were a dozen others attending the meeting by the virtual conference. I glanced around at them until I found the one I wanted. A bald woman who had chosen to adopt the more visual aspects of Cybran augmentation. Namely a crisscrossing spiders web of crimson circuitry.
"Rek;'la clean up the area, would you? Destroy the surviving Tau aircraft and then implement sanitation plan five. I want there to be no wreckage for the enemy to analyse." She nodded and a moment later her virtual reality projection disappeared from the room.
"As for the rest of you. It looks like we're implement offensive plan Delta/ three. Make sure your forces include more than one human soldier or the machines will self-destruct. And remember I want prisoners. If I find out any of you have been ignoring offers of surrenders there will be consequences, none of you wants to see what it looks like if someone removes a Cybrans implants forcibly. Dismissed!"
They nodded and one by one left the conference call, their holographic projections disappearing.
When the last of them were gone I reclined in my chair and steepled my hands in front of me. Scenarios ran through my mind at the speed that only a Cybran's mind could achieve. Something was wrong. The Quantum realm was disturbed in this time. The safety features that had destroyed the last the of the Prowlers was something that would never have bothered a Commander in the Infinite war. But here? Something was disturbing it. If a unit lost its connection via the Quantum Relm to its Commander, then it would destroy itself to prevent capture. Something was causing that to happen here if there was no human presence nearby to the units.
My small army had expanded since the raid on the airbase, but it was still no match in numbers for the Enemy. In a fair fight, they would bury me in ordinance and war machines. Luckily I was a Cybran. We don't fight fair, we fight to win. In front of me, my retina display burst to life. Information of a dozen conflict zones as formations of war machines lead by human piloted machines started to engage the Tau forces who had been deluded by their leaders lies into thinking they were the hunters and not the hunted.
In the corner of my vision, a display for the total available Quantum bandwidth to command units remotely continued to fluctuate. This was going to make things more difficult.
/
The atmosphere in the command centre had started out tense. Por'Vre Noa had insisted on being present, he and a small clutter of Water cast bureaucrats huddled in the corner, scrupulously taking notes of the various pre-battle reports from the various Tau forces as they made ready to deploy.
Shas Vre Oml had done her best to ignore him. Normally a Fire cast with the rank of Vre would be deployed on the field commanding a Cadre, or perhaps a Contingent of several Cadres. Instead, she was effectively the leader of the Fire cast Command on planet. She had better things to do than worry about bureaucrats hurt feelings.
Neither the senior Earth cast or Air cast members on planet were in attendance. Fio'Vre Kras was busy with his fellow technicians, getting as many machines as he possibly could into fighting conditions. The garrison had been operating at the tempo of a peacetime deployment. Inevitably as the tempo of operations had increased, first with the forced resettlement and then with the large-scale operation to find and destroy the as yet unknown enemy some machines had suffered malfunctions.
Kor'Vre Sly was located on the words singular orbital station. Little more than a facility to store mined minerals for ease of transport rapidly converted into an orbital launch platform for the best Air cast pilots on planet. The loss of an entire airbase with its attendant squadrons had shaken the usually cool and collected Air caste veteran. Some airbases had been abandoned on his order, to allow for a greater concentration of forces.
All told Operation Mont'Swev, (Killing Sweep.) had been planned as a large-scale offensive. Upwards of 80% of all Tau combat assets were deployed. Large formations of Remora stealth drones were prowling ahead of the main forces, probing the ground with Radar, Lindar, acoustics and Magnetic Imaging. They would find and hurras the enemy, tying them down for the main forces to smash them into dust.
Then things had started to go wrong.
First had come interference on the communications channels, unexplained static on the line. It had cleaned itself up after a few moments, and Fir'Vre Kras's voice had come over the command channel to report a faulty component had been discovered and replaced.
Then hell had erupted.
Half a dozen Earth cast communications officers had started shouting at once, reporting engagement between Tau forces and unknown hostiles. The main holographic display in the command centre flickered and then started to update itself. As contradictory reports from a dozen different engagement zones poured in it fizzled and flickered before freezing. A dozen airbases and staging posts were reporting artillery fire from unknown sources. The guards at several of the resettlement camps were frantically reporting attacks from within and without.
Most ominously of all several facilities had simply dropped off the data net completely.
/
Kor'Vre Sly took only a moment to survey the unfolding catastrophe before responding with the swiftness expected of a fighter pilot.
"Launch all craft. Double-check point defence systems, I don't what anything getting through. Get me a channel to planetside command!"
"Unable Kor'Vre, all channels are jammed!"
Suddenly the bright blue lighting of the orbital command centre was replaced with the pulsing crimson of emergency power. Kor'Vre Sly felt the familiar sensation vertigo that comes from suddenly passing from one gravity field to another. The Gravity Plates beneath him had lost power.
/
Contrary to what the Tau commanders might have been seeing on their displays, they were not facing the tidal wave of enemy forces. Even after a fortnight of diligent work I had been unable to stabilise the Quantum Network my units were used to the point where I could deploy more than a hundred and fifty-one machines. That included the Mass Fabricators, power generators and underground factories that I was using to build my forces. On top of that for some reason, the data of my higher tier units was corrupted. Meaning could only field the most basic fighting units available to a Cybran commander.
If I was some stubborn headed fool of a UEF commander, who believed that the only solution to a problem was the application of raw, unadulterated brute force, or an Aeon commander who was guided more by scripture than by good common scene then I might have been in trouble. As it was, I really had to adjust my strategies.
Whilst my various intrusions into the Tau's command and control system, made possible by backdoors created when I had first hacked the system, played havoc with their forces my own were striking at various key targets. Ammunition and supply depots, repair workshops and the like. Small bands of humans had infiltrated some of the Resettlement camps and were in the process of launching a series of riots against the camp's guards, who's strength had been bled white to provide troops for the Tau offensive.
I had also identified key individuals in the Tau military who held leadership positions, or who were eligible to inherit command if their superiors were lost. In orbit, a Commando team, carried by a heavily modified Skyhook transport, was assaulting the facility that housed the commander of all aerospace assets on the planet. The commander of the ground forces and the head of the civilian government were also being targeted. Obligingly they had decided to position themselves in the same room of the same building.
/
Twelve Zeus attack bombers flew at one and a half times the speed of sound towards the Tau command centre. They were flying low, below the Tau Radar and Lindar network that their implants helpfully added to their vision by augmented reality displays., weaving in and out of the sand dunes and gullies that lead toward the compound. Normally a Cybran might accelerate their mental capacities to times ten of normal processing speed. For this attack, the four human pilots amongst the attack force were operating on twenty times normal reaction time. Their machines had been modified prior to launching the attack, captured files showed that the Tau base had a formidable AA network. The Tau would hopefully be taken by surprise by the initial attack but calculations had placed the odds of surviving a second attack run in the face of retaliator Tau fire at close to zero. For that reason, each machine carried a ten tone bomb crudely attached to impromptu hardpoints on each wing. Flying the machines like this without them would have merely been dangerous. Flying with them was nearly suicidal. Even with all the advanced autopilot software and reflexes twenty times faster than any normal human could bost the piolets were only just managing to maintain control of their machine.
The first the Tau knew of the oncoming attack was when Fire warriors on the outer perimeter were bowled over by the air pressure of the bombers passing merely ten meters above their heads. Eardrums burst and targeting cameras in combat helmets cracked. Frantically the Shas Ui in charge of the patrol tried to raise the alarm, but his Com bead had been broken by the overpressure. He reached to his equipment belt and fired a warning flare.
By the time the base had seen and responded to the flair, the first bombs were dropping.
Half their bombload was directed at the command centre, identifiable from its location at the centre of a nexus of electromagnetic chatter. The rest were for various targets of opportunity. By the time the first Tau fire from manually controlled Burst cannons had started a thousand Tau had already been obliterated. One of the three tone Neutron bombs plunged directly into the command enter and detonated, destroying the majority of the Tau's upper command echelons in a single stroke. A dozen Orca transports, full to the brim with troops designated to act as a strategic reserve were obliterated in a moment. A Trio of Skyray missile gunship, their Seeker Missiles sitting impotently on their racks for want of reliable targeting data were consumed in the explosion of a fuel dump. Panicking crews could only sit in their machines helplessly as the internal temperature rose and systems failed. One lucky crew died quickly when their missiles detonated. The rest were cooked alive in their machines.
One of the Zeus's was brought down by a Hammerhead gunship, whos commander managed to align up his railgun on the oncoming machine and blasted it out of the sky. He didn't have time to celebrate. The burning smouldering remains of the machine, breaking apart internally from the overloading of its Structural Integrity field smashed into him. The resulting ball of wreckage carved a trench a quarter of a mile long in the desert sand. Then as quickly as it had begun, it was over. The remaining Cybran bombers were disappearing off into the night. Leaving behind a trail of devastation so complete it would take the Tau weeks to identify some of the dead.
/
Kor'Vre Sly checked the magazine on his Pulse Pistol and tried to steady his aim using a nearby console. Around him the last surviving members of the Orbitals assigned personal did the same. The unknown attackers had, over the preceding half an hour butchered the two hundred Fire warriors assigned as station-side security. Now he was reduced to the two dozen Earth and Air cast in this room. Their weapons were trembling, partly from fear and partly from unfamiliarity. All Tau assigned to a military posting received some weapons training but it was regarded as a formality for all but the Fire cast.
The camera feed to outside the blast doors of the command centre ceased transmitting. A few moments later the "clunk" of something being placed against its surface could be heard by all. Fingers tensed on triggers. Any moment now…
A Matter Reclamation breaching charge placed on the floor of the station above them detonated. So did one placed on the ceiling of the floor below. As the Tau were trying to process the changing situation Synaps grenades were hurled into the room from above and below. When they detonated Tau cried out as there own nervous systems rebelled. Por'Vre Noa had been partially sheltered by the console he was sheltering behind. His right arm hung limply by his side, but his left still held the pistol. He opened fire on the first of the black-clad attackers as they emerged from the hols in the floor and ceiling. He scored three successive hits before his target swung up his rifle and fired. Sly had heard from Fire cast veterans about the "Las Rifles" of the Imperium Imperial guard. They had described them as being accurate but light hitting, clearly this was something different because as soon as the unknown enemy pulled the trigger, his entire left arm evaporated. The pressure wave of expanding fluid was transmitted through the cells and soft tissue of his body, smashing into his internal organs and causing him to slump his last memory was of a human standing over him with a container of some kind. It was white and on its face was painted a red circle with a white cross imposed on it. Then the pain and internal damage overwhelmed him, and he drifted into merciful sleep.
/
In the end, it took the Tau commanders a full day to regain control of their forces. It wasn't just that I could shut off their communication at will. It was that I could send false orders. More than once Tau forces had blundered into traps because of orders I had fabricated, moving into pre-arranged killing fields of artillery and Mantis Assualt Bots. The distrust of the Tau forces towards anyone who they weren't talking to face to face grew as the time went on. A number of friendly fire incidents occurred that were completely unplanned. A flight of battle damaged Barracudas, returning from a savage dogfight to their home base at the main command centre were fired upon by the crews of the AA weapons, terrified that they were about to be the victim of a second enemy bombing run.
All told my counter-attack had cost me twenty-seven aircraft of all types, fifteen ground vehicles and a grand total of thirteen pilots. In exchange, we had cost the tau approximately ten thousand casualties. In truth, it wouldn't have mattered if we had killed just one Tau. Killing them had never been my goal. Far more importantly I had managed to eliminate approximately 90% of the enemy's airlift capacity. Reduced to burning wreckage of Orcas scattered over the deserts sands. Large formations of Tau troops were now stranded in their bases rapidly running through supplies, placed under a virtual siege without the need for a single jailor. The few surviving transports were now occupied running constant supply lines to the Tau forces. Whilst at all times being hunted by roving bands of Prowler interceptors fighters,.Inspite of their best efforts, by my estimate the Tau would start running out of fuel and water within a few days. If my little campaign had been allowed to continue uninterrupted then I have no doubt I would be able to gradually eliminate each of the pockets of trapped Tau forces one at a time. Alas, it was not to be.
/
Until this point my only knowledge of the warp had been random fragments of data collected via my ransacking of the Tau data net during the raid on the airbase. It referred vaguely to the Tau method of FTL which seemed to involve skimming into the Warp, another dimension of sorts that did not follow the normal laws of reality. At the time I had dismissed it as a relatively primitive species making their first forays into the use of the Quantum Relm for transport.
Then the Tau Courrier ship tour a hole in reality and dropped out of warp approximately 15 million kilometres from the planet, my atmospheric sensors focused on it automatically, for the faintest of moments I got a view of the warp in all its horrible glory before the warp rift closed itself as the laws of reality fought back. I was on my knees vomiting before I knew what was coming. By the end of it, I was dry heaving. In the corner of my eye, I could see reports popping up of other Cybrans suffering similar effects.
As a Commander my implants were more advanced than theirs and psionic dampeners buried in my brain tissue activated. I still felt like I had been run over by a tank but I was at least able to stand. It would take others hours to recover as much as I had. By then, of course, it was too late.
The Tau crew weren't stupid. When their sensors took in the numerous destroyed or damaged Tau basses planetside and the cloud of wreckage that surrounded the orbital station it swung its bow around and moving at the maximum speed it could without pulping the crew made the best speed out of the system. Half an hour later it jumped out of system.
I had known that the Courier ship was incoming, but according to my calculations, I had still had almost a month before it should have arrived. Of course, now I know that The Warp looks at concepts like order and reason and laughs but back then I had made the mistake of trusting in the predicted date of arrival I had pulled from Tau data files.
Being a minor mining base the Tau data networks on the planet were not the most up to date. However, from accessing more and more of their network in the leadup to my counter attack, I had begun to acquire some understanding of the strength of the Tau Empire, a vague idea of the size of its navy in nearby space and its industrial power. If the Quantum realm was behaving itself, allowing me to field larger numbers of more advanced units I might have been able to make a fight of it, as it was I had to do the one thing that Cybrans have done since the beginning of our existence. Run.
/
A conclusion of the inquest into the incident on XV8815.
Restricted to Etherial cast rank of Ui or higher.
The incident on XV8815 remains shrouded in mystery, even after half a year of diligent investigation by the Water and Etherial cast. There are a few facts that can be confirmed beyond a reasonable doubt. None the less outlined below is what is known to have happened.
An unknown force attacked and destroyed a minor airbase in the planets central deserts. Tau commanders attempted to retaliate by launching a search and destroy mission aimed at discovering and eliminating this force. Somehow the unknown enemy learned of this attack and launched a spoiling attack of their own. Their targets in this attack were logistical centres and officers of high rank and seniority. There are confirmed reports of the unknown enemy attackers placing themselves in danger just to have the chance to eliminate high ranking or experienced Tau personal.
Please see the attached video document that shows an unknown class of enemy fighter, (code word Spear Tip) deliberately endure attacks from Tau fighters so that it can line up a shot against the Kor'Ui in charge of this flight of Barracudas. Weather this is due to some of the enemy machines being unmanned or due to an extream commitment on the part of the piolets is unknown. The wreckage of the enemy's machines is scarce and seems to employ some kind of self-destruct to prevent analyzation.
With the loss of the upper command echelon and significant amounts of enemy interference on communication channels the Tau offensive stalled out, became disorganised and was attacked by the enemy using tactics that seem to resemble the Killing Blow, concentrating maximum force on isolated points of Tau resistance whilst other units were unable to assist due to the losses of much of the Orca transport fleet in the first day of the operation. Whether this is a coincidence or the result of an analysation of Tau tactics is unknown.
Following the blunting of the offensive, Tau forces were attacked at will, until a Courier ship arrived to receive an annual status report. After this and the Courriors subsequent flight from the system, the enemy changed tactics. Tau forces were mostly left alone so long as they remained on their bases. The only exception were those Tau forces who were involved in guarding Human resettlement camps. These camps were repeatedly attacked, seemingly with the desire to abduct the human population inside.
Interestingly enough the guards at these compounds were offered surrender and in the handful of cases when it was accepted seem to have been well treated. This is the opinion of many Tau present rules out the unknown attackers as being from the Imperium of man.
When the relief fleet arrived it found a world almost completely devoid of humans. What little remained of the orbital network detected a series of unknown starships lifting off from desert Badlands approximately a week before the arrival of the relief fleet. An internal investigation is underway to discover how these ships were able to land in the first place without being detected.
Many motives have been put forward for the unknown enemy's motivations. Until such time as a theory with sufficient evidence is produced they should merely be treated as speculation. For now, all Tau garrisons within a hundred light-years of XV8815 should move to condition two for the foreseeable future.
For the greater good.