+ inload: Space Marine Armour Marks at Calth +
As the Great Crusade wore on and the bounds of the Imperium increased, supply lines for the whole of humanity's fighting force became attenuated. Simultaneously, novel STC discoveries were routed back to node worlds such as Cypria Mundi, Hydraphur, and – of course – Mars; where the Astartes' armour and weapons were refined and improved.
These circumstances meant that the uniformity of Mark II Crusade armour, used by all Astartes at the commencement of the Great Crusade, was diluted further and further. As more Forgeworlds and STCs were brought to light, they were set to work producing materiel for the Legions at various staging posts throughout the Imperium. The inherent difficulty and delays of communication created by the size and speed of the Imperium's expansion, coupled with most forgeworld's jealous hoarding of their secrets, meant that from an early stage in the Great Crusade Space Marines wore subtly different armour.
While all information was fed back to Mars and then sent back out to the Mechanicum across the galaxy, some refinements made by individual forgeworlds were lost in interstellar communication, or were superceded at node worlds by more effective measures received from elsewhere. As a result, local variants of armour emerged which were termed patterns, based upon the forgeworld of manufacture. The original Mark II plate issued to all the legions was retroactively named Mars-pattern. The phrase 'Crusade Armour' became a common term, used interchangeably with Mark II, to describe all compatible power armour suits, regardless of their planet of manufacture.
Despite its flexibility and versatility, Crusade Armour eventually reached a point that further refinements were largely cosmetic and counter-productive as the number of patterns soared. Mars-pattern Mark III and Mark IV – Iron Armour and Maximus Plate respectively – were issued in relatively quick succession; the first a culmination of existing technology into a definitive final point, and the latter a genuine evolution of Astartes armour made possible by the Martian Mechanicum's discoveries during the Great Crusade.
By the outbreak of the Horus Heresy, no Legion remaining could be categorically stated to have all their forces in the same patterns of power armour, and most of them used a variety of marks. The Primarchs' and Legions' preferences also influenced and complicated this issue. Some favoured newer armour for veterans, while others issued the latest armour to recruits. Individuals often added, or were issued, updated or artificer-crafted elements as replacements to their existing armour; creating mongrel suits – retroactively grouped into the loosely-defined Mark V 'Heresy suit' – that demonstrate the STC system's inherent compatibility to great effect.
+ Armour of the XIII Legion +
It might be expected that the Ultramarines' organisational nous would mean the Legion could assemble in identical gleaming ranks, each line warrior a mirror of the next; but in truth the sheer size and widely-scattered disposition of the legion made uniformity a vain hope. In any case, the culture of the 31st Millennium placed more emphasis on battlefield efficacy and reliability than on an obsessive and fruitless need to 'count rivets'.
Nevertheless, the Ultramarines attempted to maintain internal consistency within individual Expeditionary Fleets, for ease of maintenance if little else. However, ongoing field replacement, resupply delays and, most of all, the yawning gulfs of isolation inherent to warp travel meant that Ultramarines Legionaries in different Expeditionary Fleets wore a huge variety of armour variants and marks drawn from all over the galaxy.
Prior to the Calth Atrocity, Ultramarines were most commonly armoured with Mars-pattern Mark II plate, because Konor – a forgeworld protectorate of the legion situated in the Macragge system – was a relative backwater. Situated on the Imperium's frontier, Konor was isolated by sheer distance from communiques from Mars, and as a result was still manufacturing relatively unsophisticated suits of power armour even as Mark III and IV were being distributed to other Legions. Even so, Mars-pattern was issued across little more than circa sixty per cent of the Ultramarines. The remainder of the XIII Legion – 100,000 or more warriors, a number that rivalled other entire Legions in in number – wore a disparate collection of Mark II variants. Notable amongst those used by the Ultramarines were Port Caros-pattern; Calth-pattern (the famed 'Praetor Armour'); Incaladion-pattern and Phaeton-pattern, all of which differed in subtle ways from Mars-pattern, but were broadly built on similiar tolerances and the parts of which were inter-compatible.
The precise choice of pattern an Expeditionary Fleet's complement of Ultramarines Astartes wore was mainly dependent on the individual fleet's galactic placement, with the Legion officers requisitioning sufficient armour to resupply his whole force in one fell swoop. As a result, a significant minority of the Ultramarines Legion – mainly those operating in the core of the Imperium – were lucky enough to be issued with the newer Iron and Maximus armour suits; by the time they were recalled to Calth. A small proportion were even operating with the experimental Mark VI 'Corvus' suits, though difficulty of repair meant that these were rarely complete, with individual components being replaced with inferior earlier parts following damage.
+ Armour of the XVII Legion +
Given the Ultramarines' disparate appearance, those with a low opinion of the Word Bearers – the only extant Legion to be reproved personally by the Emperor of mankind – might conversely expect their wargear to be more rag-tag and non-uniform. Indeed, this prejudice might be strengthened by the XVII's isolated nature on the edge of the galaxy, far from resupply; and their apparent desperate zeal in expanding the Imperium that meant their speed of redeployment outstripped supply lines.
However, quite the opposite was the case. While the Word Bearers were indeed fighting hard on the fringes and enjoying huge success in their crusade of fire and blood, the Warmaster had ordered huge quantities of Mark IV armour to be sent to the XVII as a mark of his favour. These advanced suits meant the Word Bearers suffered fewer casualties and damage even as they expanded massively. In addition, the Warmaster's patronage of Lorgar's legion was supported by the nascent Munitorum. Naively believing the Word Bearers' sincerity in their drive to demonstrate their worth to the Emperor, Munitorum officials were keen to further encourage the Word Bearer's apparent change of heart and prioritised the XVII's resupply over other Legions – sending both more and better, more advanced, armour marks.
As a result, prior to the Battle of Calth, the Word Bearer saw extended life expectancy and battle experience for their veteran forces, even as they saw a huge influx of recruits. The Legion blossomed, growing in size to be second only to the Ultramarines themselves; and with virtually every legionary resplendent in gleaming Maximus or Corvus plate.
It is rumoured that the Word Bearer forces sent to Calth were secretly selected by Lorgar from those he considered most consumed by hatred of the Ultramarines; those whose zeal to bring down the XIII eclipsed almost all other considerations. This included a disparate array of troops: those who saw their chastisement on Monarchia as an unbearable humiliation; those who saw Guilliman's legion as exemplars of the despised Imperium's values; and petty bitter brethren who could not see beyond the jealousy of the Ultramarine's reputation. These warriors ranged from new recruits raised in hatred, to veterans battle-hardened by the whole of the Great Crusade.
While the Word Bearers had already largely purged their ranks of Terrans, Lorgar also saw Calth as a chance to dispose of those unwitting few from the throneworld who had escaped both the secret massacres and survived the fires of Isstvan. These legionaries and officers included some of the oldest and most obedient Word Bearers of all. Tragically, some of these surviving Terrans were amongst the group taken into the inner lodges, who had earlier helped to plan and execute the destruction of the other Word Bearers who shared their world of birth. Some were amongst the most experienced and highly-connected Chapters, almost completely comprised of legionaries honoured with cutting-edge Mark VI plate.
Despite proving their loyalty to Lorgar beyond all reasonable doubt; following him in preference to the Emperor who had personally led them during the early battles of the Unification Wars, the Primarch of the XVII consigned these unhappy, unwitting few to Calth. Perhaps he was gripped by remorse, secretly hoping they would triumph and survive; perhaps he wanted to excise any surviving connection to the throneworld; perhaps he was already gripped by the madness of Chaos. The truth will likely never be known.
+ Assembly at Calth +
Owing to the treachery of Lorgar and the Warmaster Horus, the majority of the Ultramarines legion was gathered on the surface of Calth immediately prior to the Atrocity. While the bulk of the Legion had been stationed relatively nearby – prosecuting the Great Crusade on the expanding Eastern Fringe from staging points on the Five Hundred Worlds – this huge undertaking involved recalling Chapters, Companies, and even individual squads from as far afield as the Adrantis system in the distant galactic west, and the newly conquered territories rimwards of Cypra Mundi.
As explained above, while the gleaming cobalt blue and gold of the Legion's heraldry tied together all of the XIII, it was a common sight for two Companies to be bedecked in perfect uniformity internally, but to be wearing completely different armour patterns.
+ The Calth Atrocity +
Immediately following the initial attack, the reeling Ultramarines were forced into undignified retreat. Whole Chapters were slaughtered without firing a shot; and few Companies survived completely unscathed. So widespread and well co-ordinated was the attack, and so tightly-packed were the Ultramarines' forces, that the hours following the Campanile's destructive crash-landing saw the XIII legionaries rallying uncertainly into makeshift and hotch-potch battlegroups. Some were made up of Companies or battlegroups that had largely escaped the initial slaughter, and so their armour remained uniform; while others were battle forged groups made up of individual survivors who had managed to band together.
In the latter instance, the groups could look hugely disparate, with temporary squads marshalled from remnants. In these cases, each Ultramarine in a squad might be wearing different armour and clutching different weaponry – an impression reinforced by the need to scavenge weaponry as the Word Bearers and their allies methodically targeted and destroyed armouries, warehouses and stockpiles. However, it was more common for survivors to be found by, or attracted to, Companies that had been ravaged. In these instances, the core of the force might be wearing largely uniform armour, with a few individuals in a different pattern or mark bulking up understrength squads.
In contrast, the Word Bearers ground forces remained relatively uniform, at least in the overground theatre. With little to no effective response from the Ultramarines, the Word Bearers advanced largely unchallenged, conquering and despoiling Calth's townships, cities and barracks. Until the Calth Orbital Defence Array came back into loyalist hands, Word Bearer casualties were scattered and light, and as a result, their armour remained for the most part inviolate and uniform.
However, once the Ultramarine's automated and manned defences were restored, the triumphant Word Bearers found themselves embroiled in bitter counterstrikes, where forces loyal to Ultramar came surging forward in hastily-applied ambushes. Despite the lack of a reliable central command and control, the Ultramarines and Army units were on home ground, and were justifiably enraged. In turn, their excellent and well-prepared counter-assaults were met head-on by the bloodied edge of legionaries who had already fought that unthinkable fight: that of inter-legion warfare. The Word Bearers' experiences on Isstvan more than matched the Ultramarines' prepared practical drills, and the two forces were evenly matched.
+ The Underworld War +
Even as the Ultramarines rallied and began to fight back, the next step of the XVII Legion's plan came to fruition. Veridias, the system's star, was poisoned, driving the combatants – Ultramarines and Word Bearers alike – to seek shelter. During this period, surviving elements were often isolated, and forced to scavenge weapons and armour. The period following the Calth Atrocity saw many interesting jury-rigged armour changes and inventive temporary solutions; not to mention the peculiar patchwork appearance of red and blue marines forced to use elements of their dead enemies' armour in the desperate tunnel-fighting of the Underworld War; but that is beyond the scope of today's missive.