This is one of those dumb little pointless questions, but I'll see if I get any answers before it sinks to page 3.

In the Space Marines, we have a nice group of folks called Techmarines. These are one of my favorite character types to consider playing, and I like their options. One little quandary I have, though, is this: Tech Priests seem to resent that they were born of flesh, and as one of the few organizations not beholden to worshiping the God Emperor as a god, but rather as a manifestation of the Omnissiah, they are not required to, in the strictest sense, hold up the Human form as perfection (when compared to numerous Xenos or Mutants with superior abilities), and instead cut out various chunks at the firt opportunity, and replace them with tech, the blessed gifts of their God, in order to be closer to Him (won't the be surprised when they become Necrons?)

Anyway, Space Marines will send their own, with penchants for tech, and a willingness to be alienated by the brothers forever afterward, to Mars, and have them learn the machine mysteries of the Cult Mechanicus, who then return as Techmarines. Now, Techmarines can grab Machine (X), and slowly replace their "inferior" Human flesh with tech, too, but this confuses me. Space Marines are supposed to be like gods, in some ways, and their bodies are often viewed as the closest to perfection a Human can reach. To chop bits off, and replace them with cybernetics, just to follow a religion you kind of don't, seems odd. Add to that, a Space Marine's body is crammed with extra organs. How do you replace most of your body with other stuff, and still have all the extras that make a Space Marine what he is? And if you do, what was the point in laboriously filling him up with extra organs, just to tear them out, and replace them with "better" cybernetics? When I imagine an advanced Tech Priest, I see just enough tissue left to not be an AI robot, feared by all. They have mech limbs, lungs, blood, heart, eyes, armor plating, etc, and might even talk with a vocabulator. I find it hard to believe a Space Marine could do that, and still be a Space Marine. I'm betting they aren't quite as gung-ho about "upgrading" as their Human teachers, but I don't know. I certainly don't remember rules in book saying that they lose to gain, but that could just be to be nice. On a mechanical sense, I don't know how they do it.

If cybernetics can replicate the parts of a Space Marine removed, so that they still have all of their bits and pieces that make them awesome, it's a shame they can't make a tech "Black Carapace", so that other people can benefit from Power Armor, more, but oh well.

As an equally pointless aside, is a Techmarine's servo-arm a part of him, or his armor? The book seems to claim it is a part of the armor, meaning if he removes his armor, say while at the Watch Fortress, or in transit aboard ship, he would not have a SA, and only their own suit of armor would give them access to it. I think that Tech Priests in Ascension (amazing that DH Tech Priests never get one, when they are IG-like, and those guys have one; wonder if OW lets them get one?) have it anchored to their flesh/cyber mantle, as do RT Explorators. Do Techmarines always just have it separate, or might they, eventually, anchor it to themselves? Probably makes more sense attached to the suit, but I is curious.

Given that Space Marines almost always deploy in fully-sealed armor, being attached to the armor makes more sense. I'm thinking that perhaps a port is built into the armor that either allows an exterior-mounted servo-arm to be plugged into the marine himself (if he controls his extra limbs as such), or to simply plug into the armor and allow control from there. This both preserves the vacuum seal of the armor, and means he doesn't have to do anything awkward to put on his wargear. I can't see putting little rubber seals around the holes they drilled in the guy's armor to accommodate his extra limbs.

Regarding the special organs and such in the Space Marine and replacements there-of… I do not believe that a Techmarine can take as many iterations of "The Flesh Is Weak" as say, a tech-priest. I'm not sure about that, I don't have the Dark Heresy books myself. I'd guess that represents that the Space Marine form isn't as tolerant of full-on replacement as the standard human body is.

The Marines are capable of replacing as much of their body as they wish, (Going up to TFIW 5 IIRC) Especially the Iron Hands, who often are little more than a brain in a cybernetic body once they become ancients.

As to the Servo Arm, I would imagine that it plugs through the suit into the Tech-Mantle (whatever that Mechanicus implant is called) Space marines can remove gauntlets, helmets and all the other pieces of their armor to put it on and remove it, what's one more spot of vacuum sealing? On the other hand, I expect that the Techmarine would be wearing his armor any time he was wanting to use his Servoarm (i.e. not using it to get a glass of water from across the room without getting out of bed in the middle of the night.)

It is a mechadendrite after all, and those do plug into the nervous system via the Mechanicus implants.

Fenrisnorth said:

Ah, heck, you're right. Besides, I guess the Tech Marine would be the guy who vacuum seals everybody else's armor anyway, huh?

Fenrisnorth said:

*It's the middle of the night-cycle. All is silent in the shared chamber as the Kill-Team is transported to their next mission, all brothers lying on their backs in silence.*

*The groaning of a servo arm. It slowly clamps down on a glass of water, and draws the cup slowly towards its wielder's mouth*

*The Assault Marine suddenly sits up stock-straight from across the room*

"ARE YOU SERIOUS!?"

Servo-arms are anchored to the armor and interfaced with via the spinal nerve port and/or power armor/black carapace interface.

Take off the armor and there is not an effective anchoring point or power supply for the servo-arm.

"Ports for these detachable arms are attatched at the shoulder, and the Battle Brother's armor must also by upgraded to include auto stabilizers to use one effectively. "

That looks to me like it plugs into the Marine himself but he needs to be in his armor to get full usage from it. His Potentia Coil should supply any power necessary.

Ugh there's a long set of quotes I typically reply to this with, but I am currently too lazy to dig them up. Suffice to say I wouldn't allow them to be used without the armor.

Both the physical models and most [if not all] art for tech-marines show that servo arms and other such arms are attached to the backpack of the armor, which also looks like a unique construction.

I'd agree it can't be used per the rules without the armor to stabilize it, lest the 14SB tear the the marine's body apart, but It's a mechadendrite and thosare a cybernetic, which attaches to the body, not an armor upgrade.

I personally allowed a custom cybernetic that allowed a servo arm to be mounted onto an astartes without the need for power armour (Augmented Bracing 30req, Distinguished) because I have my lads in Scout armour a fair amount.

Fenrisnorth said:

The writing is incredibly inconsistent regarding cybernetics. What are typically called "bionics" appear in some part to be a subset of cybernetics which are organic replacement structures (replacement arm, replacement eye, MIU in the head, servitors replacing legs with treads, etc). Non-bionic cybernetics might be attached to hardpoints, though modular hardpoints are not at all a feature of Imperial technology aside from pintle weapons, Terminator gear (and that is more of a long ritual than plug-and-play) and dreadnought weapons (same as Terminator equipment).

Generally I feel like cybernetics can be attached to/detached from the body but bionics are not removeable. Under those definitions I'd call mechadendrites cybernetics but not bionics.

Keep in mind also that attaching to the armor does not make it an armor upgrade. Maybe a direct neural port works fine…except it's completely unable to be supported even by SM physiology.

I can see examples and benefits for both, but it would seem then that only the Space Marines, the most physically robust of the individuals who wear servo-arms, attach them to armor. Many Tech Priests wear power armor, but some don't and they are able to anchor the apparatus right to their bodies/cyber mantle, so I wasn't sure if a Techmarine could/would do the same. I don't know if their Mechanicus Implants include all the stabilize/reinforce extras that a TP gains, that allow their bodies to survive being attached to lifting a hull plate of a Leman Russ on a battlefield. On the other hand, I think I like it being a suit add-on more; they might look more normal, by Space Marine standards, when seen without their armor, if they don't have a giant crane jutting out behind them. Granted, TMs aren't invited to all the parties, but keeping up appearances can be important.

Given the text for the servo arm from Ascension [where it was first seen?] the person in question is modified with a heavy 'frame' to support the weight and strength of the servo arm. The only reason an Astartes wouldn't [normally] do this is because they usually have no reason to. Power Armor is all the framework they need to support a servo arm. If you want to go into more detail think of this. It is easier to repair or maintain a servo arm that isn't directly attached to your body. It is also easier to maintain the marine himself if the servo arm can be removed easily, and power armor supports that much better than direct integration does.

You also have to think of the shape and design of the power armor itself. A tech priest would be fine with a shoulder or back mounting for a servo arm because he doesn't have to worry about an enormous power pack for his armor, if he is wearing power armor at all. A space marine does. His armor requires a great deal of power, and you can't just get rid of the other functions stored in the power pack because you want to directly attach a servo arm to the marine. You can't do shoulder mounts either because of the large, shield-like nature of the shoulder pads on a power armor. They move a whole lot with armor movement and are designed to protect, not serve as an anchor for additional limbs. Overall the power pack is simply the best place to put a servo arm. It is strong and can be reinforced easily, it is tough, it is out of the way of the marines normal arms and it is a direct power supply.

You know, I just meant to type something short and I ended up with two paragraphs.

Space marine bionics are noted as being of higher quality than normal human equivalents. They use the "common-exceptional-mastercrafted" scale, which to my mind represents the extra craft and specialist materials needed to make bionics that can endure use by space marines. The Iron Hands are noteworthy for being able to create bionics that can replace space marine flesh without them losing combat efficiency.

Servo-arms are mounted on power armour which is connected to the space marine. No exceptions in my book.

Fenrisnorth said:

The reactor strapped to the Space Marine's back probably handles all the necessary power requirements. Likewsse he doesn't need a special port on him somewhere for the Servo-arm to hook up to, as it can run through his armour, which is already connected to his nervous system through the Black Carapace.

That it's listed under mechadendrites doesn't mean that it MUST plug directly in to the character's body somewhere. Nothing says you can't have it a permanent atachment of course. I'm sure in the case of the Iron Hands and other Chapters of a similar bent it wouldn't be rare for a Marine to have that. But I think generally it's something that is integrated in to their armour.