Intro - Design Aims
The design of this Marine is to match the official Marine armour template created by the legendary Jes Goodwin. It seeks to justify the image of Space Marines 'as is' in the background and draws upon information known about the Space Marines in published material and comments by the design studio. My aim was to create a Marine that is 100% compliant to the Warhammer 40,000 background, and explains some of the 'rule of cool' quirks - like Marine heroes always seem to be 'bigger' than other Marines, and the discrepancies between stated sizes in the background.
This work is a fan fiction 'hypothetical', one possible explanation that while unofficial does support the Marine as seen in Warhammer 40,000. I started with the Marine armour template created by Jes Goodwin, which is the 100% official Games Workshop template. I then created a derivative 3D model from this, which I later used Later used in my cover artwork for the Black Library. An example of such as the cover of 'False Gods'. However, I have never been asked to create an image of an unarmoured Marine. To avoid any confusion see the disclaimers below;
What follows is unofficial fan fiction...
Space Marines and Power armour
Marine morphology goes far beyond what we, with our modern day perspective, consider the limits of human body extremes. Unlike us, the humans of the Imperium are familiar with human extremes that fall far outside what we consider natural. What we may consider an abnormal human body morph would not be rare in 40K. Much of these extremes are the result of Dark Age genetic manipulation of colonists. The humans that conquered the stars are not like us. The largest of the supermassive morphs of human are classified as 'Ogryn' some of which best Marines for sheer mass. As such, the human population cline of the Imperium contains extremes that fall outside our current cline. It's these extremes body morphs that are recruited in the Adeptus Astartes, and usually at a young age. No one alive in our world today, comes anywhere near the sheer physical power needed to become a Marine recruit.
Armour Match up
I started out with the standard Space Marine template drawing by Jes Goodwin. This artwork is GW's official template of a Space Marine and shows the officially correct proportions of a Marine. I used this as my base template though I repositioned the legs to be closer together for modelling purposes. My aim was to match my 3D model to the Marine template as closely as possible while maintaining a shape that would allow a reasonable Marine body model to fit inside. Some modification to the design had to be made to make the body look anatomically correct, while being suitably heroic (strong man), but I hope my model retains the character of the Marine. Jes discusses his view of Marine design in the fourth instalment of the design studio podcasts: Design Philosophy IV: Jes Goodwin Interview. In it, Jes says he thinks of Marines as 7' to 7'6" with a mass of four basketball players 'bolted together'.
I say seven to seven foot six, because actually if you read the novels they get progressively bigger every time we write a novel.
Jes Goodwin, podcast 4, 30:26
and;
Because you know, if you wanted to take basketball players you'd need to bolt about four of them together to get the bulk.
Jes Goodwin, podcast 4, 31:55
Design notes
The 3D model on the right was used in my Black Library covers, such as 'Tempest', 'Warrior Brood', and 'Warrior Coven', and modified in 'Philhammer' pattern of armour for the Sons of Horus, as seen on the cover of the False Gods novel. More can be seen on my 3D page.
Armour and Marine
The armour is designed to be a second skin and fully integrates with the Marine via the Black Carapace interface. The power armour has a similar thickness to a modern day IFV or APC, though using advanced ceramics, and offers excellent protection against small arms fire. A powered exoskeleton is used to offset the weight of the armour. Neuro-Fibre Bundles (NFB) provide this motive power; each NFB runs through channels within the superstructure frame plates of the exoskeleton. The outer ablative armour plated are bolted onto these frame plates.
Flesh vs NFB/ MW (Neuro-Fibre Bundle/ Muscle Wire)
[Notes: Neuro-Fibre Bundles are incredibly powerful but use tremendous amounts of energy to produce that power. NFBs produce a lot of heat, and can drain more energy than most man portable [backpack] systems can supply. While is is theoretically conceivable to build an Android out of NFBs (Iron Men) there would be no power system compact enough, of cooling systems efficient enough, to run the Android and keep it mobile (technology lost). Therefore relatively little NFBs are used in Power Armour. In Marine version of the armour, the ratio of NFB power and power plant is carefully balanced and optimised. Most of the strength of the Marine comes from his body, not from the Power Armour.
Each NFB is routed through the inner frame plates themselves. The stops the NFB slicing through the Marines own flesh like a cheese wire. It also means that power armour can seem a little thin, as there is no underlying 'muscle suit' between the Marine and the armour. The armour is self-contained and the 'under suit' does not contain any NFBs (Only the Black Carapace interface, and body coolant systems, all sealed up from the environment, along with a contact gel for hygiene).]
Marine diagram with skeletal and musculature overlay
This diagram shows an overlay of the Marine skeleton over flesh, which in turn I overlaid onto the Marine template. I modified the armour to my personal preference in the overlays. Compared to the official Marine model I created on the right (without the overlay) the most notable change is in the design of the armour covering the legs, hip exo-supports and faulds (hip armour). I drew heavy inspiration from the 'Rogue Trader' armour style.
Muscle Mass Comparison
This chart is to give an idea of exactly how massive a Marine is. The Marine dwarfs a regular sized (real world western average) human to the far left. In full armour (far right) the Marine is significantly more massive. Much of the Marines power is not 'magical' but due to sheer bulk, improved muscle (ape/ Neanderthal?), and the increased muscle leverage due to the placement on the modified skeleton. The Marine is strong in the same way a chimpanzee's or silverback gorilla is strong. It's not magical just damn powerful by design!
Power: Combined with their power armour a Marine would find it very easy to move a regular human: a shoulder barge would go though most linebackers, door, and brick walls with ease! A punch would likely take an ordinary person off their feet and hurl them several metres through the air. A Marine is massive enough to grab a regular human by the ankles and wield them like a cheap club to beat their way through a crowd (until the man-club disintegrated from the impacts, but in a crowd, there are plenty of 'weapons'! As humans are 'bendy', they're probably a bit like wielding Nunchaku in a round about way 
)
Physical Power
It should be noted that while the Marine is large, they are not built like a body builder. The skeletal frame of the Marine is restructured to produce the morphology shown in the previous diagrams. The power a Marine can generate is fundamentally different to that of a body builder, as a Marine is not 'muscle bound' (over muscled) like a body builder. A Marine has more in common with a powerlifter and shares a similar frame though much larger. The Marine is also not tall like a person suffering from gigantism, which builds on a weak frame for the height, they are tall as if it was their 'natural' height (though there is nothing natural about a Marine!)
Frame and Agility
To get an idea of the power of a Marine think 'gorilla'. A large silverback gorilla will usually top out at around 450lbs. The Marine is around 780lbs, but has a bigger chest and legs, so the Marine's arms are probably similar is power and size to a silverback gorilla. Which brings us to the question of agility - how can a bulky body as large as a Marine's be agile?
The are a number of reasons, first: ever seen a gorilla charge? They aren't slow! Even bounding along on all fours they can cover ground quickly and easily catch a human (and barge through the undergrowth like it wasn't even there!). A Rhino is pretty big but can outrun a human. Half a rhino is pretty heavy and supported by two legs: so natural bone and muscle can support quite a bit of weight on two legs. A Marine is probably physically able to run as fast as a human, maybe a bit quicker due to the length of their stride.
Vulnerability
A Marine is very large (and fast) which is great for a punch up, but not so great in war. The simple fact is that humans have been taking down animals which are far larger and faster than themselves since they first evolved (or created). If humans can kill tigers and woolly mammoths, a human the size of the Marine is not a problem, in fact even our myths glorify taking on those larger than ourselves: David and Goliath. A Marine's size alone is not threatening to a human warrior, they may be intimidating if you are unarmed and unskilled, but a warrior would see it more as a 'challenge'. I'm sure a hero like Achilles would not be intimidated in the slightest.
What makes a Marine powerful is not their size, it's their intelligence, tactics and gear. Without their armour a Marine is highly vulnerable to weapons fire - but why so big? Two reasons;
First; one is that it allows them to wear thicker armour, and this thicker armour is enough to defeat most small arms carried by humans and biped aliens alike. A Marine is virtually immune to the vast bulk of an enemy's small arms. To get an idea, a Marine is covered in armour that is superior to modern APCs or IFVs. A Marine is effectively a one man IFV!
Second: Marines were originally utilised in the crusade to retake human world that posed a real threat. Often worlds that posed a real threat retained STC technology or have STC derivative technology. When deployed, during the crusades, Marines were often running around in STC structures which can accommodate their size, and makes it difficult to bring heavy weapons fire to bare. Though Marines in novels are running about in the open, this should be thought of as an exception (it's dangerous, perhaps reckless, but makes for good drama as the Marines will face powerful weapons). Charging around STC bunkers (often a Marine target) the Marine will face small arms and the occasional hard point. They can, therefore, be very fast and 'reckless' (by regular human standards for similar situations) and take down and enemy HQ very quickly.
Notes: It's unclear if original Power Armour, like the Mark 1 Thunder Armour was based on STC. This type of armour appears on Terra, Caliban. etc. so it may have been STC and therefore universal during the Dark Age of Technology. What we do know is that Thunder Armour was not all encasing like 40K era Marine Armour. Therefore it would not have offered invulnerability to small arms fire. Without immunity to small arms fire, being huge is a disadvantage in a firefight, and the Techno-Barbarians of Terra may not have been as large as proper Space Marines. This would hold true for the rest of human civilisation.
There again the Techno-Barbarians are known for grappling which is not a primary form of combat when armour fails to stop ranged weapons. Medieval knights could run around the battlefield as arrows were not an issue (unless fired at point blank range), but as soon as firearms turned up, it quickly fell out of favour. So how did they end up in CQC?
Perhaps the Techno-Barbarians combat was more about honour than real warfare - i.e. two leaders fight to the death in hand-to-hand combat, and the winner takes all, thus reducing the loss of life. Making the techno-barbarians 'champions' of powerful cartels and corporations who fight in vicious gladiator matches to settle corporate disputes? Or power fields for protection, and power armour for up close and personal combat.
Growth and Maturity [optional]
This section deals with the variations in Marine size found throughout GW and BL publications. It's entirely possible for such variations to be natural. Some Marines may simply grow taller than others. This does raise an interesting curiosity should this be the case, that in 40K: Marine heroes tend to be depicted as being taller than 7' and more often 8'. To go back to a previous quote;
I say seven to seven foot six, because actually if you read the novels they get progressively bigger every time we write a novel.
Jes Goodwin, podcast 4, 30:26
Could it be that the larger Marines are more heroic than shorter Marines? This idea would further play into Western ideals of heroes being exceptional by bloodline, and there is nothing wrong in that interpretation, but on its own, I find it a little 'narrow' in vision. It could do with some more variations added into the pot. What follows is an additional way to explain why Marine heroes tend to be taller;
Legacy
Marines are the 'sons' of their Primarch. The Primarchs were very tall; a Primarch is as tall to a Marine, as a Marine is to a man. As an [exceptional] man is transformed into a Marine they take after their Primarch, growing taller and stronger over time. Often they pick up physical features and personality traits of their progenitor. The longer a Marine survives, the more like their Primarch they become. My idea that follows plays into that by extending the assumed end of the transformation process. Instead, the transformation process continues to affect the Marine in some small way even after they have become a full battle-brother. I'm not suggesting that a Marine could ever become as massive as a Primarch, merely that the transformation process takes a lot longer to wind down.
Note: This concept of extended transformation could tie into specific Chapter traits. One example is the Blood Angel's curse. The curse is where a Blood Angel becomes destined to fall into the Black Rage due to their Primarch's death scream. As the transformation process continues to affect them for a much longer period, sooner or later, they will become so in tune with their Primarch's psyche: that they start to see visions. The curse may be due to the Blood Angle's practice of blood transfusion during the early stages of the transformation process - where they mix a little of their Primarch's blood in with their own. This may allow the shattered warp image of their Primarch to cling to the small portion of his (actual) blood running in his son's veins. His blood is kept alive within his sons. The longer the Marine lives, the more influence their Primarch has, and a Primarch's soul (even a fragment) is far too powerful for a Marine..
Back to the concept;
Size
Due to their rapid bio-recovery systems, a Marine is always in a constant state of rejuvenation and continues to grow for many centuries after completing scout training. Though their growth will eventually decline with age, it takes millennia for the Marine bio-systems to reach a state of 'dynamic equilibrium'. Due to their work, it is highly unlikely a Marine will ever be in a state were age debilitates them. Even the great Lord Commander Dante, Chapter Master of the Blood Angels is still growing [according to me], but at a significantly reduced rate. His healing bio-systems are still top notch and he could survive for many millennia to come. It is also notable that now he is 'mature' for a Marine he is starting to develop minor psionic powers such as precognition and looking ever more like his beloved Primarch and the holiest Imperial Archangel: Sanguinius.
Stages and Height: Marine scouts are a minimum of 7', most tactical Marines with a century under their belt are around 7'6". After this, the growth rate slows but doesn't stop and the chapter heroes who are many centuries old are around 8'. Very few grow past 8' (ignoring genetic anomalies).
- Average Human: This is a person of 5'9". No Marine initiate is of this size. I marked the growth line on the diagram with a dotted line as a hypothetical.
- Neophyte: Chapters recruit aggressive young men to be Marine initiates, from a population of exceptional fighting stock, and a track record of violence. Recruits have to be a minimum of 6'6" with many being closer to 6'9". It is rare for humans larger than this to be taken as often such great size is down to growth abnormalities (gigantism) rather than a stable gene pool of feral warriors.
- End Phase neophyte (Scout): This is the Neophyte in the end phase of training and the minimum height when a Marine gains the final implant of the Black Carapace. Each suit of Space Marine power armour is customised to fit using pre-sized modular components. However, no modular components are made that would fit a frame of less that 7'.
- Marine: Marines continue to grow for the first couple of centuries of being a full battle-brother. During this time a Marine's armour is upgraded at regular intervals of around 5-10 years. As they outgrow armour plates, they pass them down to up and coming Marines, and the now larger Marine accepts the gift of armour components from a more senior battle brother. The passing of armour plates is a bonding ritual. A Marine will not pass his armour components onto a lower status marine he considers unworthy. During this stage of Marine development, many new Marines are lost to war. Many of the armour plates given to new Marines are 'new' issue, often reconditioned parts (repaired battle damaged armour salvage). Due to this fact, it is considered an honour to receive a 'cast off' from an older battle brother who is living, a mark of respect, and these plates are considered 'blessed'.
- 'Terminator'*: Once a Marine reaches an age of 2 centuries or more; their growth rate is practically zero. They no longer have to change armour plates, and their armour gains more and more honours becoming exceptionally ornate. At this level, the armour is only handed on after death. It is these 'fully grown' and stable Marines that can fit into, and are entrusted with, the greatest of the Chapter's armour relics: the mighty Tactical Dreadnought Armour.
*Apart from the Space Wolves
Armour Notes: Marine armour needs to be increased in size as the Marine grows. The exoskeletal superstructure is adjustable with sliding plates, but the ablative armour plates are not. As the exoskeleton superstructure adjusted to match a Marines increased size, artificers simply sculpt material to the ends of the ablative armour plates. (If you filed off the paint from the plate you would see 'growth rings' towards the end.) A Marine, who is 8 foot tall, is considered 'mature', but most will not make it to this age. The average Marine is around 7'6", but ranges from around 7'3" to 7'9" for a tactical Marine during their service. Most of their early and rapid growth is taken up during scout training. Hence the scout style of armour which is free plates and cloth. Chapters could have used conventional Power Armour technology for Scouts, similar that employed by the Sisters of Battle. I dare say a Chapter would do this if resources were unlimited, but the scouts grow so fast, and die in such huge numbers, it is impractical. (and the Adeptus Mechanicus would have a fit!)
The undersuit of the armour is a custom fit, and the artificers often change out the Marine's undersuit.
Terminator Honours, Allocation of Armour, and size
Most chapters will only allow those Marines who have proved themselves time and again in battle, and who have long service records, to gain Terminator armour honours. In the process of proving themselves worthy, by acquiring honours, the Marine matures and usually is at least a couple of centuries old before they have enough chops to gain Terminator honours. Even so, there are limited numbers of Terminator suits. Getting to wear the Terminator armour is not just being about age and size. Due to the limit stock, only the current 'best of the best' will be allotted Terminator armour as needed. A Marine may receive full Terminator honours and training and be eligible to wear Terminator Armour, but never actually get to wear a suit of Terminator armour in battle. This is due to those in line before him with more 'honours'. Due to this limitation, many fully mature Marines with Terminator honours wear power armour instead. As such, any Marine will have to survive long enough to see a senior brother die before they can take his Armour.
This whole process means that most Terminator honoured Marines are taller than regular Marines, and seem much taller due to Terminator armour being bulky and adds more height than power armour (a regular Marine would seem taller in Terminator armour than power armour). A Terminator Marine is very tall, and this gives a full range of 'Marine' height of 7'6" to 8' in Power Armour, and as tall as 9' for an 8' senior Marine in Terminator armour. As an aside, Terminator armour is more restrictive compared to power-armour, and this suits the older Marine as they are slightly less agile than younger Marines.
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