Power Armour

Power armour is an advanced form of armour, worn primarily by the Space Marines and the Chaos Space Marines. It is a completely enclosed suit of armour, made of thick ceramite plates. The armour would be heavy and cumbersome to wear but for the electrically motivated fibre bundles within the armour that replicates the wearer's movement and enhances his strength.

Design
Power armour is fully sealed, isolating the wearer from the outside environment and protecting him from gas weapons and harsh atmospheres. It also commonly includes numerous auxiliary systems such as communicators, auto-senses, etc.

Space Marines go through an arduous process where they receive various implants culminating with the implantation of the black carapace which allows the Marine a direct and instinctual interface with the armour, making it in effect a second skin. The advanced systems of Space Marine power armour also monitor the Marine's biological functions, feeding the medical information to the Marine.

The backpack contains the main power plant, environmental system and additional stabilizers.

History and development
Power armour has been in use since before the Age of the Imperium, worn by the techno-barbarians that dominated Earth during the Age of Strife. It was also worn by the pre-Space Marines that formed part of the Emperor's retinue during his unification of Earth towards the end of the Age of Strife. At the armour's earliest incarnation, the suit was not fully sealed or life-supporting, this being unnecessary while its use was still confined to Earth. Over the history of the Imperium, power armour has developed into many different forms. Need, circumstances and recovery of new materials and technology has shaped the armour's evolution.

Mk1 Thunder Power Armour
The first Power Armour created for the Space Marines. It was developed from the armour worn by the techno-barbarians that plagued Holy Terra near the end of the Age of Strife. It was used during the Emperor’s campaign to retake and unite the Terran solar system before the Great Crusade. It was by no means unique to the first Space Marines - in fact, the techno-barbarian warriors the Emperor fought during the conquest of Terra wore it too, and the Emperor's forces were wearing it even before the first Space Marines were developed. However, because it was designed with Earth-fighting in mind, it is not fully enclosed, with no means to support the wearer in a vacuum. Only the upper body is powered, due in part to the fact that during the Conquest of Terra, ranged weapons were difficult to make due to technological constraints, and so a warrior's upper-body strength was his most important asset. It takes its name from the thunder symbol the Emperor had before adopting the double headed eagle.

Mk2 Crusade Power Armour
It was developed towards the end of the Age of Strife and was used during the dawn of the Imperium during the Emperor’s Great Crusade to retake the lost worlds of man. It was designed as a fully enclosed suit with life-sustaining systems that now allowed the Space Marines to fight in deep space and on alien worlds with hostile atmospheres or environments. The armor was made up of circular armor rings fitted under and over each other, making this armour relatively tedious to repair (see also Lorica segmentata). These precious relics are still used during ceremonial procedures by some chapters and given to champions as battle armour in others. These suits are also referred to as Crusader Armour.

Mk3 Iron Power Armour
As the Great Crusade reached the planets towards the center of the galaxy, some of the worlds encountered were the Squat Homeworlds, which were not pleased to find themselves the object of galactic conquest. High casualties suffered by the Space Marine Legions led to the development of the mark 3 power armour, suitable for the conditions being fought in - boarding actions and confined tunnel complexes with little cover. This armour was ideal when cover was minimal and combat was a matter of frontal assault.

Mk3 was intended to be a specialised suit to provide heavier protection. The frontal armour was much thicker (thereby giving greater protection), but the rear armour was thinner to compensate. The wedge-shaped helmet (designed to deflect incoming fire) formed the basis of the distinctive Corvus beak helmet.

Mk4 Maximus Power Armour
This armour was to be the replacement for the old Mk2 armour of the Great Crusade.; It was the first armour to incorporate many components used in modern armour. However, it was made from rare alien materials, and when the Horus Heresy broke out soon after it was issued, it was discovered that most chapters cut off from supplies could not find the materials needed to make it or repair it, and they often suffered irreparable damage by relatively minor battles.

Mk5 Heresy Power Armour
This armour was developed as a solution to the supply problems of the Horus Heresy. It was easily made from the most basic of materials, and it was easy to maintain. Almost all soldiers used spikes to hold the armour layers together, making the studs shown universally on all examples of this armour. In time, it became traditional for the studs to be found on the head, lower legs, and left shoulder pad of the armour.

Due to the sub-standard materials used in the construction of this armor variant, it had a tendency to over-heat quickly, and many marines had to endure sub-standard performance by turning down the power output of their backpack to prevent intolerable heat build-ups.

Mk6 Corvus Power Armour
This classic variant can be traced back to the time of the Horus Heresy and is still commonly used in contemporary Chapters. It is characterized by the beak-like muzzle on the helmet and a studded Auto-reactive shoulder plate on the left shoulder of the armour. The beak or muzzle led fans to nickname this variant "Womble armour" or "Beakie armour", and a dictionary of the Orkish language in the 2nd Edition Ork Codex listed Marines as "beakies". This was the style of the first Space Marine models released by Games Workshop and did not get its Mk6 terminology until after models with the Mark 7 styling were released. Models with this style were not part of new releases until the launch of the next range of 25 mm plastic models.

Mk7 Aquila Power Armour
This armour was also known as Imperator Armour. It is the contemporary variant most commonly used by the Space Marine Chapters. The Mk7 armour is characterised by the grim looking Vox caster (external vocalizer) on the faceplate, and the plastron displaying the Imperialis (a winged skull), which has given the armour different names such as Armorum Impetor or Eagle Armour ("Aquila" being the name of the two-headed eagle which symbolizes the Imperium).

Mk8 Errant Power Armour
This is an update to the Aquila pattern armour, and is distinguished by a raised collar at the front, and armoured plating for the torso cables. Full versions of this armour are almost never seen; however, it is common to find parts of it being used by officers and veterans on the battlefield.

Design Notes
One design feature of Mks 6 through to 8 is their adaptability; it is fairly common within most Space Marine chapters to see a suit combining parts originally created for three or four suits, salvaged from dead brothers on the battlefield. Mk 7 armour, in particular, was created with this simple modularity in mind.

Other Imperial Users
Although Power Armour is most closely associated with the Adeptus Astartes, is is also used by the Sisters of Battle, Grey Knights and some Inquisitors. However, they do not possess the black carapace implant, and so can not be directly linked to the suit's advanced systems in the way Space Marines are, which decreases the armour's effectiveness.