Mezoan Campaign - Onto the Crucible of War: For historians, most of the great battles of the Horus Heresy are difficult to reconstitute -- too much data has been lost in the fires of that conflict or through the slow erosion of time. Even more has been sequestered purposefully by the authority of the Holy Ordos of the Inquisition or following the Edicts of the High Lords of Terra. It is fortunate that this is not the case for the Third Siege of Mezoa. Of these sources, the greatest wealth of information comes from the war chronicles of Nârik Dreygur, the de facto commander of the Iron Warriors' 114th Grand Battalion.Although numbering in the thousands, the first wave of enemy dropships essentially carried pact-conscripts from Moab and other Imperialis Auxilia troopers who had declared for the Warmaster. Both were considered inherently expendable by their Legiones Astartes overlords, especially Autilon Skorr who commanded the Traitor armada. No defence cannons or flights of slaved Mechanicum drone-interceptors met the incoming assault wave -- Mezoa's guns remained eerily silent as the Magi had decided to turn to far more dangerous weapons: the wrath of Mezoa itself. Set deep beneath the stable crust of Mezoa's outer mantle, great subduction furnaces were used to hurl vast projectiles of magma and bedrock into the skies, each projectile easily measuring a kilometre in length. Against this weapon, the Traitor gunships and dropcraft stood no chance and the casualties proved devastating. Those few dropships that did manage to safely land on the ash-covered surface were eagerly awaited by packs of vicious Vorax-class Battle-Automata. Their Power Blades massacred the isolated Traitors and chased the scattered survivors into the caves and sulphurous crevasses of Mezoa's mantle where they would slowly choke to death, brought low by the heat, ash and toxic gases released by Mezoa's intense volcanic activity. Of the Traitor invasion's first assault wave, none survived, but unfortunately for the Loyalists, its intent was never to establish a proper beachhead but to provoke just such an aggressive response.Autilon Skorr, the Traitors' leader, had correctly assumed that the Mezoan Magi would not be able to constantly maintain the exotic bombardment that had annihilated the first assault wave. Unless they wanted to entirely destroy their world or dangerously compromise its tectonic stability, the barrage would have to relent at some point. The massacre of the Traitors' first assault wave had achieved just that. Loath to squander his own troops in the bloody affair that was a planetary drop, Skorr placed the 114th Grand Battalion at the heart of his second assault wave, supplemented by what battle-hardened mortal troops remained. Encountering only conventional anti-air fire, the second assault wave suffered only minimal losses until it reached the volcanic, ash-shrouded surface of the defiant Forge World. Amid the scarred corpses and burnt-out wrecks of the first wave, a message reached Dreygur and his grim, iron-clad veterans. It was a message from Autilon Skorr informing them that each vessel trying to leave the surface in retreat would be shot down by the Alpha Legion's guns.Now with no other option save victory, the Iron Warriors and their auxiliaries dug-in, transforming their drop-ships into makeshift bastions which would anchor their defence lines. Soon, the Loyalists rushed in, ready to chase the Traitors off their world. Under a hellish glow produced by the great magma-geysers that illuminated the battlefields, the Iron Warriors fought with a ferocity unmatched, save perhaps by those Legionaries that followed the bloody path of the XII Legion. Each Iron Warrior that fell killed at least three attackers in return, the 114th Grand Battalion demanding a steep price for every Terran inch of ground captured by the Loyalists. At the battle's climax, Nârik Dreygur faced the commander of the Loyalist detachment, the Imperial Fists swordsman and Champion Valtus Moran, and slew him, his cortex-controlled Battle-Automata tearing Moran's corpse to shreds, leaving the Loyalists to quit the field. At the end of the first solar day, the sacrifices of the Iron Warriors had secured a landing zone for the Traitor armada.Soon the ash-plains at the edge of the great forge-fanes of Mezoa were swarming with activity. Sokar Pattern Stormbirds, amongst the heaviest vessels that were able to safely land on Mezoa's fragile surface, formed great bastions of overlapping Void Shields, their combined power great enough to repel the ground-shaking impacts of lava-coated bedrock flung against them. Soon both sides were firmly entrenched and facing each other over a short span of no-man's land. Using their superior numbers, the Traitors tried to push the attack home, their artillery trains targeting the forge-fanes' fortifications, creating breaches where Autilon Skorr mercilessly ordered his massed mortal auxilia to attack. Wherever the strength of the enemy seemed too much for mortal or Mechanicum soldiers to overcome, Skorr dispatched the 114th Grand Battalion, keeping his own Alpha Legion Astartes in reserve, shielding them from attrition wherever he could. While the Iron Warriors suffered mounting casualties, the Alpha Legion used the distraction caused by their allies to act as headhunters and raiders, targeting isolated Loyalist command units or sensitive installations and retreating to their lines before a counterattack could be mounted.This did not mean that the Loyalists were content to sit idle while Skorr prosecuted his assault. The defence of the walls and fortifications fell to Mezoa's own Taghmata-forces and the heavy infantry of the Lethe Solar Auxilia Cohorts, thus freeing the Legiones Astartes contingent for more dangerous tasks. Reinforced by the remaining elements of the Imperial Fists, Xiaphas Jurr split his Disciples of the Flames into demi-companies of about 50 Astartes. These detachments conducted a series of spoiling attacks and lightning raids intended to disrupt the enemy's efforts. The Mezoan Magi supported these limited forays into enemy-held territory, isolating enemy troop concentrations by letting entire regions of the ash-plains collapse, burying the Traitors under a tidal wave of fiery lava or collapsing the enemy trenches upon them. The disorganised and isolated pockets of resistance were then cleansed by the Loyalist Astartes. Elsewhere on the battlefield, the Tech-adepts resolved to use suicide cohorts of Adsecularis Auxilia or Battle-Automata to lure the enemy into pre-planned kill-zones where great blasts of magma would annihilate friend and foe alike.As with all things, the Mechanicum Adepts of Mezoa kept detailed records of their expenditures during the battle. Traitor and Loyalist casualties were compiled and run through mathematical simulations that would determine the Forge World's best response to the ever-changing tactical situation. Despite the small victories and the Loyalists' mastery of the terrain, the cold arithmetic of war did not favour Mezoa.