The Assault of the Tempest Galleries is the rare battle of the ancient Unification Wars that united Ancient Terra under the control of the Emperor of Mankind in the late 30th Millennium that is still recorded in Imperial archives.
The Caucasus Wastes was a techno-barbarian state located in the Caucasus Peninsula of the ancient European continent on Old Earth. Its despotic ruler, known as the Ethnarch of the Caucasus Wastes, was defeated by the forces of the Emperor and imprisoned in the maximum security Imperial prison in the Himalazian (Himalayan) Mountains known as Khangba Marwu or The Vault.
Although it is entirely likely that the transhuman warriors of the XVIIIth Legion saw action before their assault on the Caucasus Wastes, the records of these engagements being either deliberately lost, deleted or sealed at the highest level, the first open battle honour recorded for the then-as yet unmatched XVIIIth Legion was the assault on the Tempest Galleries during the overthrow of the Ethnarch of the Caucasus Wastes on Terra. It would also prove to be one of the most famous early campaigns for the Legion. Even though it occurred long before the XVIIIth Legion's reunification with their Primarch Vulkan on Nocturne, this conflict set its seal upon the nature of the Legion and had a profound influence that remains to this day.
The conquest of the Caucasus Wastes was one of the last great battles of the Unification Wars that would see at last the Emperor as the undisputed master of Terra, but victory did not prove easy. The mutated eugenicist-oligarchs who ruled the Caucasus Wastes presented the Emperor's forces with one of the most difficult challenges they faced in open warfare. While few in number compared to the zealots of the Yndonesic Bloc or the savage warbands of Ursh, the Caucasus Ethnarchy's power was based on scores of relic-technologies and the terrible weapons in their possession which dated back to before the Age of Strife, while its military forces ranged from the armoured, gene-augmented "Ur-Khasis" troops, roughly analogous to the Emperor's Thunder Warriors, to narcotically-enslaved covens of psykers. The Ethnarchy's strongholds were concealed kilometres deep beneath the hollowed-out mountains of the Wastes and shielded from attack from above by near-impregnable power-filed webs. An attempt by the Imperial forces to take the Ethnarchy's mountain-strongholds by storm earlier in the Unification Wars had met with bloody defeat, with the loss of almost 10,000 Thunder Warriors and more than a million other casualties, but had seen the Caucasus Wastes contained and isolated thereafter. So it was that when the hour of the Emperor's vengeance came around, nothing was to be left to chance.
The forces of six entire proto-Legions of the Legiones Astartes were mustered for the final assault on the Caucasus Wastes, along with the massed forces of the Legio Custodes, with the Emperor Himself to lead them, and countless other tributary armies, mechanised battalions and warrior bands beneath the raptor-and-lightning banner of Unification. But, of all of these, the first thrust upon which all else would depend the Emperor entrusted to the nascent XVIIIth Legion. Although the decision to utilise what they considered to be a largely unknown and untested unit in so vital a role was questioned by many within the Imperial command, the Emperor's will was obeyed. The XVIIIth would carry the assault, utilising scores of freshly created gigantic "Termite" subterranean boring machines fitted with recently acquired technology from Mars.
The full force of the proto-Legion, some 20,000 Astartes strong at this juncture, was committed to what was widely believed to be a suicide mission to destroy the vast geo-thermal furnaces which provided power for the Ethnarchy's impregnable defences. These were housed far below even the subterranean strongholds, and known of only through ancient legend, in a hundred-kilometre-long string of vast, artificially-created caverns known as the Tempest Galleries for the incessant storms of flame and electromagnetic force which bled from the ancient and little-understood relic machineries. The XVIIIth Legion's Power Armour had been specially-modified for the extreme conditions they were to face, and had been camouflaged in striated patterns of sulphur yellow and sable black. Once they were ready, the XVIIIth saluted their Emperor and calmly mounted the untested Martian war engines of the Mechanicum and pierced the dark earth and rock at the edge of the Wastes, disappearing into a deadly and unknown world.
Soon all signals were lost, and not even the power of the Imperial psykers could penetrate the turbulent depths to maintain contact with the Space Marine assault forces. Hours stretched into days and days became weeks, and nothing was heard from the assault force while the vast army of the Emperor waited in immediate readiness for the grand attack, and no sign or signal came. Pressed by His commanders, it is said the Emperor silenced them and replied; "They shall not fail me, they will return from the fire, thus it shall ever be."
Reports claim that moments after the Emperor spoke, great tremors shook the region, their turbulence felt as far away as Gorodak and the Jade Citadel of Hangol. In their wake, the power-webs that had for so long shielded the Caucasus Wastes failed and the full force of the Emperor's wrath fell upon them to their utter destruction. The last Ethnarch of the Caucasus was dragged in chains to the Imperial prison of Khangba Marwu and the buried secrets that had been his strength were taken by the new, now uncontested master of Terra. Of the fate of the XVIIIth Legion nothing was known until the closing days of the campaign when, far from the Wastes, a long-dormant volcano near Klostzatz shattered and one of the Termite machines hauled itself from the rubble carrying just over a thousand survivors from the XVIIIth Legion. The taskforce's after-action reports were immediately analysed by the Imperial command structure, and had they not been accompanied by supporting evidence and hololithic records, it is likely that they would have been greeted with disbelief.
Almost four-fifths of the XVIIIth Legion's taskforce had survived the journey to their objective, the rest being destroyed by the plethora of environmental hazards, crushed like eggshells between the grinding tectonic plates or incinerated by seas of magma when their shielding failed. Those who breached the carborundum-lined caverns of the Caucasus Tempest Galleries found a strange, imprisoned world as alien as anything the expeditions of the Great Crusade would find among the stars. Vast kilometre-high spindle-machines turned over caged seas of molten metal drawn from the planet's core, spewing forth coronas of blinding lightning while suspended on silicate webs across which unfathomable and inhuman machines scuttled like spiders. In this airless furnace beyond mortal endurance, the Legionaries of the XVIIIth found no warrior of the Ethnarch to contest them, for nothing human had set foot in this hell for millennia, but rather the defenders of these sleepless engines, that had turned since before the start of the Age of Strife, were fire-blackened service-automata reacting to the outsiders' threat as antibodies would against an invading infection in a living body.
Incredibly strong and built to withstand the ravages of the firestorm that surrounded them, each would have overmatched even the battle-automata of the Mechanicum's Legio Cybernetica in size and power, being products as they were of Mankind's ancient and technologically advanced past. There were thousands of these tempest-automata, and all turned on the Astartes of the XVIIIth Legion in an implacable and unceasing attack. Neither Plasma nor Melta Weapons could breach their armour, while Bolter shells rippled across them like rain. Only massive kinetic force applied at close range against their articulated joints was able to disable them; a lesson that cost the XVIIIth hundreds of lives to learn as they were forced into a running battle of attrition with the relentless machines, and cut off when many of their Termite carriers were targeted and crushed by the colossal articulated toothed metal spheres used by the ancient workings to tunnel and expand the galleries. The XVIIIth Legion held out with a mixture of stoic resilience and suicidal fury, maintaining discipline and order despite the onslaught, while individual Legionaries hurled themselves willingly to their deaths to grapple with the killing machines so that they might be destroyed and their brothers' lives saved.
Fighting now for survival from gallery to gallery, they collapsed tunnels and severed the silicate webs behind them to impede their pursuers and buy themselves time, but their casualties were huge, with thousands having perished within the first dozen hours of the conflict, but the precious time they had purchased with blood, however, would be spent well by the survivors, for it would be neither the Legion's immense resilience nor its willing sacrifice that would see them victorious, but their intelligence. Showing the aptitude for technology and craft for which they would become justly famed in later centuries, they began to first use the wreckage of the attacking machinery that surrounded them as salvage to repair and augment their own expended wargear, and soon escalated to tearing from the automatons their central control systems and repairing them sufficiently to be sent crashing back into their own ranks as mindless berserkers. This proved only the start; power conduits were re-directed and machine death-traps created, cyclopean lightning-rods conducting the power of the howling electromagnetic corona above were fashioned into improvised harpoon weapons to burn out the hearts of the largest machine-beasts, rivers of molten metal redirected into service tunnels, atomantic chambers compromised to detonate like miniature suns, shattering engines that had endured for tens of thousands of Terran years.
Soon something like a stalemate had been achieved, but at a terrible cost; for less than a third of the XVIIIth Legion's original number remained, and yet the body of the vast system had been badly wounded, but a mortal blow was not yet struck. In the inaccessible deeps, the ancient implacable Machine Spirit (Artificial Intelligence) that bound the Tempest Galleries together was manufacturing fresh robotic soldiers for its cause, and that was something the Legionaries of the XVIIIth Legion could not match. Realising this strategic reality, the Legion hatched a plan to commit its forces to a single, coherent attack and destroy the Tempest Galleries or die trying. The plan was to attack and cripple the central power transmission node in the largest of the gallery chambers yet discovered, the reasoning being that, even if the vast generator-spindles were not put out of action, it would successfully interrupt the flow of energy to the Ethnarch's defences far above. A two-pronged assault strategy was devised. The first division would mount a series of diversionary attacks at other locations to confuse the enemy. Once this was under way, the second, larger division would assault the power node. It was assumed that while survival was in any way unlikely for the Space Marines of the XVIIIth Legion, death for the central assault force would be certain. For this reason, the XVIIIth Legion's surviving commanders acquiesced to the wishes of the Legion's rank-and-file and assigned Legionaries to it by lottery -- not because they had no volunteers for the main assault force, quite the contrary, but because it was the fervent wish of all to take part.
When the assault came, the Legionaries thundered from their holdouts and defensive redoubts, many armed with improvised Power Fists and Thunder Hammers, Shock Cannons and cutting saws fashioned from the shattered remains of fallen tempest-automata. With them came their full reserves of munitions and manpower, for nothing was or could be held back. Attacked suddenly from many fronts, the inhuman intelligence which oversaw the Tempest Galleries responded with cold machine logic, efficiently dividing and dispatching its forces to deal with the threats. The fighting was savage but the plan was working, and the concentrated force of the main assault group managed to smash its way into the Great Gallery, its few remaining Dreadnoughts and rapier batteries leading the way. Like a hive of ants crudely kicked open, the tempest-automata responded in a tide of scorched-black metal and snapping servo-claws, slamming into the XVIIIth Legion head-on across the silicate bridges suspended between the sea of fire below and the hurricane of corposant lightning far above. Bodies by the hundred, machine and Legionary alike, fell broken into the burning abyss, severed power cables sparked furiously, mechanical bodies exploded in sheets of fire and shrapnel, while spilled blood vaporised to steam in the superheated air.
Slowly, tortuously, the Legion fought its way to the towering power node at the centre of the gallery, buying each metre of ground taken with dozens of lives. It was then the kraken rose from the depths. A vast articulated beast-machine appeared, the greatest of the robotic engines that maintained the Tempest Galleries, sheathed in armoured scales of synthetic black diamond, molten metal running off it like water. Its coils could have crushed a Battle Titan and were more than sufficient to enwrap and shatter the silicate bridge on which the Legion fought. Their weapons utterly useless against the new foe, the survivors were forced to attempt a fighting retreat they knew was futile as, one by one, the silicate strands were severed and hundreds more fell to their doom. What occurred next can only be guessed at, but the last garbled transmission from the Great Gallery was of one of the huge grav-propelled tunnelling-spheres used by the tempest-automata crashing through the gallery wall and plunging past the kraken-engine and directly at the node-nexus. It is believed that the only possible explanation for this is that one part of the diversionary attack groups had used the confusion of the battle to gain control of one of the colossal serrated tunnelling-spheres and set upon using it as a last ditch weapon.
Regardless of the cause, whether Legion-action or the calamity of one of their own automata gone haywire, the node structure exploded, collapsing the gallery around it and blowing out numerous surrounding caverns and tunnels, and creating the earthquakes and tremors felt across the region. The explosion also appears to have murdered the governing Machine Spirit of the galleries, for in the aftermath, the automata simply shut off, the machinery stilled, the vast spindle generators sinking slowly and silently into the fires below, never to turn again.
Little more than 1,000 Legionaries of the 20,000-strong XVIIIth Legion survived, and those who did were scattered across the Tempest Galleries, many conducting diversionary attacks at its fringes and once again displaying formidable fortitude and perseverance in regrouping and intelligence in rebuilding one of the damaged Termite transporters for the arduous journey back to the surface. Upon their return, the Emperor Himself gathered the survivors together and awarded them the Laurel of Victory for the campaign against the Ethnarch (to the dissatisfaction of some commanders) to be forever theirs, and their first battle honour, inscribed with the motto: "In Fire and Darkness Tested." This was to prove prophetic, and the action at the Tempest Galleries a high bar indeed for the Legion's prowess, and a standard of sacrifice and victory against the odds that would prove a punitive taskmaster for the Legion in the early years of the Great Crusade. It is an interesting addendum to the record of this battle that the XVIIIth Legion's survivors brought with them from the Tempest Galleries metallurgy and machine craft predating the Age of Strife, the secrets of which, in addition to being given over to the Imperial Command, were retained by the XVIIIth Legion itself.
- The Horus Heresy - Book Two: Massacre (Forge World Series) by Alan Bligh, pp. 115, 132-135