Astartes Wargear: Power Armor

Astartes Power Armour is an extraordinarily sophisticated defensive system that combines immense resistance to physical damage with a sensory array and a sealed environment, protecting its wearer from the ravages of the void and alien atmospheres. Integrated with the armor are networks of electromotivated fiber bundles that mimic and augment the muscular strength of the wearer, as well as connection cables that hook up to the Black Carapace implant of a Space Marine. The true genius of the design, however, lies in its close integration with the already superhuman physiology, senses, and reflexes of the Space Marine within. Working in concert, armour and Astartes together become a weapon without equal.

Below are the most common patterns relevant to the Great Crusade.

Mk I “Thunder”

Prototype heavy armor, never used by the Legiones Astartes.

Mk II “Crusade”

The first true Astartes power armor. Iconic silhouette, widely used in the early Great Crusade. Largely replaced by Mk IV and of late, the Mk V.

Mk III “Iron”

Optimized for boarding actions and heavy assaults. Heavily armored frontal plates. Superseded the Thunder pattern in those roles, but has in turn been replaced by Tactical Dreadnought Armor.

Mk IV “Maximus”

The pinnacle of Great Crusade engineering. Sleek, advanced, but costly. It is still being produced, but the focus is shifting towards the cheaper Mk V. 

Stats: PT 40, DR 60, ST +4, RSL +2

Key features: Each suit contains many subsystems; only those who provide a concrete game effect or in-universe capability are mentioned here.

• Hulking size: Astartes are big even without their suits, but when armored, they become hulking giants.
• You have Advantage on melee attacks vs non-Hulking opponents, and they have Disadvantage on melee attacks against you. 
• Note that, since the Combat Blade is a Close weapon, you do not gain this bonus while fighting smaller opponents (but you also don't get any penalty).
• Neural interface: The armor links directly into the wearer's nervous system through interface ports inserted into the Black Crapace, allowing the Astartes to wear the suit like a second skin (that, and endless hours of familiarization training). 

• No movement penalties for wearing heavy armor.

• Electromotivated fiber bundles: Not only does the suit offset its own weight, it actually further enhances the wearer's already considerable strength.

• ST +4 (to melee damage, Athletics checks like jumping and lifting, etc).
• Speed +2 (on top of normal Astartes speed of 14; humans are speed 12).

• Auto-senses: This is a complex suite of subsystems that provides the Astartes with a high-fidelity 360° active/passive sensory image of his surroundings. His vision extends far into the infrared and ultraviolet. Audio pickups ensure even the faintest auditory cue can be picked up. He can sense anything he touches or treads on as if he were unarmored, even the wind against his "skin." Olfactory sensors are also present; however, to actually "smell the roses," air filtering must be turned off. The only sense not accounted for is taste. If an Astartes needs to taste something (for whatever reason), he needs to put it in his mouth.
• Allows the wearer to use their senses unimpeded.
• There are protective filters built into the system, protecting the wearer's senses from being overloaded.
• Provides near-perfect low-light vision (a further enhancement to an Astartes' already good night vision) and highly accurate thermal vision, effectively allowing you to ignore darkness, smoke, and some other types of obscuration.
• The system seamlessly projects the gathered data into your optic nerve, allowing you to gain the benefits of using a Major action on your Vigilance check by only spending a Minor action, and the benefits of a Minor action when spending only a Free action. There is no additional benefit for using a Major action (use your auspex function for that instead).
• The active part of the system functions as a standard Imperial auspex system (an all-spectrum active scanner) in terms of range, data provided, and revealing your own presence. 

• Targeter sub-system: Closely tied into the sensor suite is a targeting system optimized for use with Legion wargear. The system will calculate ranges, target movement/deflection, optimum fuzing, and much more. Astartes are so well-trained on the system that they hardly need to think about using it to gain full effect.
• Game effects: While making a ranged attack using an Astartes weapon capable of interfacing with the suit's targeter, ignore 1 instance of Disadvantage.

• Vox suite: This is more than a radio set. It is a highly powerful, reliable, encrypted datalink. Yes, it allows you to communicate with your battle brothers, but also transmits key positional and sensor data, essentially enabling all friendly Astartes to share battlefield awareness. The system also automatically patches through to other subnets and uplinks, creating a robust battle net that cannot easily be disrupted or jammed.

• Backpack Unit: The suit's "backpack" contains a compact power core, waste heat management system, and a set of micro-thrusters for ultra-low/zero-G operations. The backpack also features an extended nutrient reservoir (see below) and a set of tools and spare parts for in-field suit maintenance.
• The armor has enough stored power for a few hours (at most) of operation without the backpack, but it will gradually shut down as power is directed to critical systems. Eventually, it will become nothing more than an iron tomb. 
• Without a functioning backpack, heat management, especially in a vacuum, quickly becomes problematic, and a careless Astartes can cook himself alive long before he runs out of power.
• The thrusters are only powerful enough to work in space or in airless, low-gravity environments like Luna. 

• Sealed suit: The suit is fully sealed and pressurized, capable of operating in a hard vacuum, and is highly radiation-resistant. It is also rated for operations at pressures of up to 20 atm (with special seals, this can be extended to 70 atm). This is equivalent to 200 meters of sea pressure on Earth, but while PA can operate in an aquatic environment, it is primarily designed for operations in dense atmospheres.
• Damage to the suit can compromise its integrity, but the suit features multiple redundancies, self-repairing subroutines, and tools/parts for patching it up in the field.

• Life sustainer: The suit can efficiently recycle waste products from the wearer and extract water and oxygen from the surrounding atmosphere. 
• Air supply in a hard vacuum is only 24 hours unless extra tanks are carried. If no air is available, the Astartes must enter suspended animation using the Sus-an Membrane.
• Combined with a reservoir of high-density nutrients, an Astartes can fight at full efficiency for one day without eating (or up to one week with the backpack). After that, the wearer must either resupply, scavenge (Astartes can eat almost anything thanks to the Preomnor), or accept a gradual reduction in biological operating efficiency.

• Bio-monitor & autodoc: The suit continuously monitors the wearer's health (and transmits the data to the unit). The autodoc can administer a range of painkillers, stimulants, and anti-toxins to bolster the wearer's already formidable constitution.
• Game effects: Resilience defense +2.

• Armored greaves: The mag boots are the most iconic, but the greaves also have a selection of retractable spikes for walking across icy or other treacherous surfaces.

Mk V “Compliance” (can't call it "Heresy" lol)

Cheaper and faster to produce, and easier to maintain, the Mk V is both bulkier and heavier than the Mk IV. It starts to appear by the mid-late Crusade era as a means to equip ever more Astartes being churned out.

Stats: Samke as Mk IV.

• Key features: As Mk IV, but simplified and ruggedized.