Whilst power armour is most commonly associated with the Space Marines of the Adeptus Astartes, the Sisters of Battle and many Inquisitors also use powered armour of one sort or another. It did not escape the notice of the Raven Guard Legionaries that the conical faceplate design had a distinctive avian look to it, its beaked countenance looking the part of hunting birds of prey. After the helmet is replaced, it make take a few more minutes for the suit's Auto-senses and full vox link to become available, as the armour's Machine Spirit takes time to reactivate after an abrupt reawakening.

This habit of gaining information about a situation by scent is so natural to the Space Wolves that many feel slightly disoriented and claustrophobic when forced by circumstances to don their helmets. To the idiosyncratic beliefs of those within the Legion, the phenomenal protection the armour provided was due to the ritual rune patterns the circuitry formed, which they believed armoured the warrior's soul as much as it did their flesh, while Imperial observers dismissed this notion as mere superstition and pointed to an underlying, if ill-understood, technological basis to these rare and uniquely forged suits of armour. Older patterns of power armour are reserved for ceremonial guards or used as the badge of office of high-ranking officers. It may be noted that there appears to be a steady improvement in engineering and design through the years. Mark VIII armour was an adaptation of Mark VII armour, both in the lore and in real life. It was actually the third suit of power armour to be designed, though among the last to appear as a miniature. However, the forces of Chaos do not have access to the resources of the Imperium, including its massive foundries, forges, manufactoria, and supply depots. Many suits of power armour were originally Imperial in manufacture, having fallen into the hands of Renegades centuries or even millennia ago. Though they may have started with their systems entirely intact, standard years without proper maintenance and replacement parts means certain sub-systems may no longer be operable.The Space Marines in the first Warhammer 40,000 plastic kit (the now famous RTB01 box) wore Mk. VI power armour. The RTB01 models were meant to have boots like the first Imperial Space Marine, but the injection moulding technology of the late 1980s made it impossible. Instead, they were redesigned with flared greaves, a design that’s been synonymous with Space Marine power armour ever since. Despite the added risk this practice presents, or perhaps because of that added danger, many Astartes see this practice as an honourable act of courage and even defiance to the Emperor's enemies. The Mark II's helmet was originally fixed to the gorget, meaning it would not turn with the wearer's head. When Forge World released sets of Mark II armour, they redesigned the helmets to enable more modelling options. The helmet was also the first part of the armour to be designed, drawn first in early concept sketches, with the armour then designed to match. The Mark II Cawl Pattern Bolt Rifle is wielded like an extension of a Primaris Space Marine's weaponised physique.

Mark VI Corvus Power Armour deployed on the Raven Guard and Iron Warriors Legions during the Horus Heresy. Unique is the suit of power armour that survives a conflict unscathed. Through long Terran centuries of combat, hundreds of repairs, and the corruptive influence of the Warp, Chaos Power Armour can change radically in appearance over time. Ignatus Armour is no exception, and it is not uncommon to find suits encrusted with religious iconography, inscribed with holy runes of warding, or inlaid with subtle defensive systems. An Adeptus Mechanicus schematic of the common components that make up a set of Mark VII Aquila Power Armour.It is fairly common to see a Space Marine in combat without his helmet, especially among sergeants and officers, and many Astartes choose to remove their helmet when there is no immediate danger present. Mark X Tacticus and Gravis Power Armour Modular Design Elements (variants for Intercessors and Inceptors displayed) Techmarines also wear a form of Artificer Armour. These suits are rarely as old and venerated as the others possessed by the Chapter, but are essentially suits of power armour that have been heavily modified and improved by several generations of Techmarines. This armoured suit is commonly referred to as "Crusade Armour," since it was designed with the planned Great Crusade in mind. It was the first fully enclosed suit of Imperial power armour, making it suitable for the conquest of space and operations in a vacuum, and thus is actually considered the first true suit of power armour. It was designed as a fully enclosed suit with life-sustaining systems that now allowed the Astartes to fight in deep space and on alien worlds with hostile atmospheres or environments.

Since the fighting on Terra during this period was primarily close-quarters, the strength of a warrior's chest and arms was of paramount importance. The legs of this armour are not powered at all, but are enclosed in tough padded breaches, though simple steel plates were sometimes also used.

Mark III Space Marines

Ignatus Power Armour provides the following benefits to its bearer: The suit's removable helmet contains the equivalent of integral, high-quality photo-visors (providing the user with darkvision and the ability to see in multiple spectrums of light, as well as making the wearer immune to the effects of photon flash grenades), a vox micro-bead, and an integral auspex sensor suite. Although power armour is most closely associated with the Adeptus Astartes, it is also used by the Sisters of Battle and some more martial-minded Inquisitors of all three of the Holy Ordos. Space Marine Power Armour is an extraordinarily sophisticated defensive system which combines huge resistance to physical damage with a sensory array and sealed environment which protects its wearer from the ravages of the void and alien atmospheres. Integrated with the armour are networks of electro-motivated fibre bundles which mimic and augment the muscular strength of the wearer. The true genius of the design, however, lies in its c