Power Armor of the Legiones Astartes
Mark II Crusade pattern Power Armor
Mark II Power Armor was designed by the Emperor in the closing days of the Unification Wars. Covering the entire body and capable of withstanding a previously unprecedented degree of punishment, this void sealed and radiation shielded suit of battle plate interfaced with the Black Carapace to synchronize the electro-fibre musculature with the wearer's reflexes. So robust was the design that these suits could function for days, if not weeks, without resupply.
Overall, this was a major improvement over the original Power Armor the Thunder Warriors were issued and it would form the basis for which all subsequent forms of Power Armor would be built and improved upon.
So successful was the design that even though the Imperial army outnumbered the Legions thousands of times over, it would be the grim visage of the Mark II helm that humanity would associate as the symbol of the Imperium in its infancy.
By the time Mark IV had begun to supplant this design, many millions of suits had been manufactured across the galaxy to supply the Legions as the prosecuted the Great Crusade.
Mark III Iron pattern Power Armor
Mark III is a specialized, up-armored variant of Mark II plate that sacrificed speed for durability. Designed to increase the survivability of Astartes in Zone Mortalis operations, Mark III was primarily issued to Legionaries assigned to boarding assaults, bunker clearing, and conflicts in the confines of hive cities.
So immediately successful was this uparmored design in Zone Mortalis conditions, that it would be the basis for the Tactical Dreadnought Armor program only a few years later.
Due to the relative ease of uparmoring a Mark II suit into Mark III during the time it is manufactured, some Legions, such as the Imperial Fists and the Death Guard, largely replaced their Mark II plate with this variant, as their preferred style of warfare was especially suited for Mark III. Even Legions who preferred the generalist design of Mark II had a high demand for additional suits of Mark III, leading to several million suits being manufactured.
Mark IV Maximus Pattern Power Armor
Mark IV Power Armor was a radical redesign of Astartes Power Armor utilizing the many technologies rediscovered throughout the Great Crusade with the first suits being manufactured a little more than a decade before the Ullanor Crusade. Maximus variant plate was meant to showcase Imperial dominance across the known galaxy and bring a new image to mind when one thought of the Imperium.
There are several key differences between Mark II and Mark IV, the most apparent being the abandonment of the separate abutting plates in favor of larger inflexible armor casings incorporating flexible joints. Mark IV plate provided greater agility to its wearer and was noticeably more durable than even the last refreshes of Mark II Power Armor.
It would be the Ullanor Crusade where the armor proved itself worthy of adoption, as some legions were initially hesitant to replace the venerable Mark II design. The Sons of Horus, then known as the Luna Wolves, were the earliest adopters and put the superior battle plate to good use, slaughtering the Greenskins in the battles leading up to Ullanor. At the crusades end, it was discovered by the Primarch who had come for the Triumph, that the Luna Wolves had taken disproportionately fewer losses compared to the other legions present for the campaign, despite providing the bulk of the present Legiones Astartes forces.
From this point onward the replacement of Mark II plate began. By the time of the Solar Triumph, most Legions had around half a million suits of Mark IV Power Armor in active use.
Mark V Corvus pattern Power Armor
Mark V Power Armor began as a long term research project to improve and eventually replace Mark IV, but was quickly changed into a specialized Power Armor variant when the Raven Guard demonstrated the promise the initial prototypes had for Reconnaissance and skirmish warfare. Something considered rather ironic by Imperial historians as the Iron Warriors had famously rejected the prototypes in favor of heavier forms of Power Armor. Eventually, all of the Emperor's legions began to issue Mark V.
Its legacy of being an attempt to improve upon the Mark IV pattern gave this make of Power Armor several advantages. The power routing and auto-senses were more efficient. Power systems had back up redundancies without increasing the weight and the auditory and olfactory sensors were much improved.
What made it so ideal for the Reconnaissance Companies of the Astartes Legions was its newly designed emissions baffling suite. Legionaries that would previously have been detected due to the emissions of the Power Armor were now capable of sneaking up upon and ambushing unsuspecting enemies. The results spoke for itself and by the time of the Solar Triumph most legions had well over a hundred thousand suits in active use.
Mark VI Phalanx pattern Power Armor
Mark VI Power Armor is the culmination of over two hundred years of technological rediscovery. Designed at the behest of several Primarchs, Mark VI is at its simplest, an uparmored version of Maximus pattern Power Armor intended to supplement, but not supplant, Mark IV.
By the time the Interex Coalition War erupted, Mark IV Maximus pattern Power Armor had all but replaced the aging Mark II Crusade pattern Power Armor in the Emperor's legions and Mark V Corvus pattern Power Armor had recently become available to every legion's Reconnaissance Companies.
Attention was quickly turned to the ancient Mark III Iron pattern Power Armor with the intention of using newly discovered knowledge to design a superior suit of Heavy-type Power Armor.
Instead of simply adding the additional outer ceramite plating to suits of Mark IV, the Mechanicum intended for Mark VI to be designed from the ground up to incorporate the heavier plating.
Mark VI Phalanx pattern Power Armor would be the end result. Each suit was far more agile than its Mark III predecessor and boasted easily replaceable modular armor coverings.
The secret to its increased agility is thanks to the STC for Power Armor recovered by the World Eaters from the Auretian Technocracy. The STC containing the knowledge on the creation of much more efficient electro-fibre musculature.
Mark VIs modular armor plating would prove capable of being replaced in a matter of minutes when damaged, a stark contrast to the hours it would take to do the same on a similarly damaged Mark III suit.
Production would officially begin in the third decade of the Interex Coalition War, and by the end of the war and the declaration of the Solar Triumph almost every legion had several hundred thousand suits of Mark VI Phalanx pattern Power Armor in active use.
AUTHORS NOTE: The name of this armor and part of the idea came from The Legions Reborn project.