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They're looking for army guys, the bright yellow marines can just slip right past.

 kirotheavenger wrote:
They're looking for army guys, the bright yellow marines can just slip right past.

Brilliant move.


Automatically Appended Next Post:

Deadnight wrote:
A good example of marine stealth was operation sedna during the badab war. Due to plot reasons, they couldn't assault directly. So instead, A combined force (iirc couple hundred...)of Raptors and Salamanders made planet fall a few hundred kilometres from their target. Over the course of 3 weeks (I think) they moved on foot towards the location and once in position launched a devastating attack.

Those Marines were indeed taking things with calm and patience... Covering 15/20km a day is something most conscripts can do without a huge stress... Since they are superfast superninjas probably they were ussing that three week period as an undercover holiday.

 Vector Strike wrote:
Well, Raven Guard marines do the 'stealth giant' thing pretty well

Actually, it would be more reasonable to state that they are the best Space Marines at stealth and that pretty much all of their operations fall under the umbrella of clandestine operations. That doesn't mean they are actually all that good at it compared to let's say, the best light recon infantry regiments of the Imperial Guard or the best recon Hunter Cadre of the Tau (who literally have invisible dudes).

Vatsetis wrote:

 kirotheavenger wrote:
They're looking for army guys, the bright yellow marines can just slip right past.

Brilliant move.


Automatically Appended Next Post:

Deadnight wrote:
A good example of marine stealth was operation sedna during the badab war. Due to plot reasons, they couldn't assault directly. So instead, A combined force (iirc couple hundred...)of Raptors and Salamanders made planet fall a few hundred kilometres from their target. Over the course of 3 weeks (I think) they moved on foot towards the location and once in position launched a devastating attack.

Those Marines were indeed taking things with calm and patience... Covering 15/20km a day is something most conscripts can do without a huge stress... Since they are superfast superninjas probably they were ussing that three week period as an undercover holiday.

do those conscript do it through an active warzone while taking an indirect path through the area to purposefully avoid enemy patrols?

No? then not comparable also a few hundred kilometers is a pretty vague word, 400 kilometers for example is "a few hundred" and assuming a 20 kilometers a day pace, you're looking at 20 days to make that trip.......
gee THATS APPROXMIATLY 3 WEEKS!

epronovost wrote:
Actually, it would be more reasonable to state that they are the best Space Marines at stealth and that pretty much all of their operations fall under the umbrella of clandestine operations. That doesn't mean they are actually all that good at it compared to let's say, the best light recon infantry regiments of the Imperial Guard or the best recon Hunter Cadre of the Tau (who literally have invisible dudes).

The Raven Guard are noted as being so good at stealth that even Space Marines struggle with them.
There is a scene in one of the Uriel Ventris novels where five Raven Guard hide in the shadows during a gathering of the Ultramarines masters of the Chapter, including Sgt. Telion one of the best Scouts of all, and not a single Astartes (barring Calgar and Tigirius who knew they were on world) even noticed them until they revealed themselves. IIRC Ventris even mulls on the idea that the entire command element of the Chapter could have been wiped out before they could raise their weapons.

BrianDavion wrote:
do those conscript do it through an active warzone while taking an indirect path through the area to purposefully avoid enemy patrols?

That's basically the basic standard of operation for light infantry. You try to avoid falling in enemy ambush and try not to get located.

No? then not comparable also a few hundred kilometers is a pretty vague word, 400 kilometers for example is "a few hundred" and assuming a 20 kilometers a day pace, you're looking at 20 days to make that trip.......
gee THATS APPROXMIATLY 3 WEEKS!

Hence why it's not that impressive. It's the sort of feat you would expect from Imperial Guard soldiers.


Automatically Appended Next Post:

 Gert wrote:

epronovost wrote:
Actually, it would be more reasonable to state that they are the best Space Marines at stealth and that pretty much all of their operations fall under the umbrella of clandestine operations. That doesn't mean they are actually all that good at it compared to let's say, the best light recon infantry regiments of the Imperial Guard or the best recon Hunter Cadre of the Tau (who literally have invisible dudes).

The Raven Guard are noted as being so good at stealth that even Space Marines struggle with them.
There is a scene in one of the Uriel Ventris novels where five Raven Guard hide in the shadows during a gathering of the Ultramarines masters of the Chapter, including Sgt. Telion one of the best Scouts of all, and not a single Astartes (barring Calgar and Tigirius who knew they were on world) even noticed them until they revealed themselves. IIRC Ventris even mulls on the idea that the entire command element of the Chapter could have been wiped out before they could raise their weapons.

Which doesn't make any sense to "hide in the shadows" since ALL Space Marines have perfect night vision and night vision helmets. They see in the dark. You can't use darkness as cover against a Space Marine. They see perfectly well in the dark and so do Eldars, Tau and Necron (and most elite human troops) either thanks to their helmets or their good ol' peepers. What you have here is called "gak writing" where the author of that scene forgot the rules of his own universe. For that scene to make sense, either the Raven Guard used a spell to conceal themselves or Space Marines actually don't see in the dark.

epronovost wrote:
Which doesn't make any sense to "hide in the shadows" since ALL Space Marines have perfect night vision and night vision helmets. They see in the dark. You can't use darkness as cover against a Space Marine. They see perfectly well in the dark and so do Eldars, Tau and Necron (and most elite human troops) either thanks to their helmets or their good ol' peepers. What you have here is called "gak writing" where the author of that scene forgot the rules of his own universe. For that scene to make sense, either the Raven Guard used a spell to conceal themselves or Space Marines actually don't see in the dark.

Or, and hear me out, the Raven Guard stealth ability is exceptionally good. Raven Guard are said to be able to literally melt into darkness and shadow, which you could take as hyperbole but when it's a repeated concept across the board and not just one writer then it's hard to dismiss. How are the Tanith so good at stealth? They're just humans with camo cloaks. Could it be because their training and skills mean that they excel where others don't? No that couldn't possibly be true.

 Gert wrote:

Or, and hear me out, the Raven Guard stealth ability is exceptionally good. Raven Guard are said to be able to literally melt into darkness and shadow, which you could take as hyperbole but when it's a repeated concept across the board and not just one writer then it's hard to dismiss.

How is that even an argument? Being skillful implies that you are great at avoiding detection "standing in the open" isn't being good at avoiding detection. It's the opposite of that. Space Marine see in pitch darkness. Standing in the shadows is basically standing in the open. This scene is simply terrible at describing any sort of stealth skill or it implies Marines don't see in the dark neither with their eyes and neither with their equipment.

How are the Tanith so good at stealth? They're just humans with camo cloaks. Could it be because their training and skills mean that they excel where others don't? No that couldn't possibly be true.

Both. They have no armor to speak off, soft clothing, great stealth doctrine and adaptive camouflage equipment. They also aren't 8 foot tall giants built like armored doors hiding in the shadows (that takes pretty big shadows to hide such big people) from people who see perfectly well in darkness. That's why they are believably competent. They have a mix of skills, tools and body shape appropriate for stealth and even then they aren't perfect.

epronovost wrote:
How is that even an argument? Being skillful implies that you are great at avoiding detection "standing in the open" isn't being good at avoiding detection. It's the opposite of that. Space Marine see in pitch darkness. Standing in the shadows is basically standing in the open. This scene is simply terrible at describing any sort of stealth skill or it implies Marines don't see in the dark neither with their eyes and neither with their equipment.

So standing completely in the open, as you put it, yet being completely unseen by people who have natural night vision isn't skill. Mk. Whatever my dude.

 Gert wrote:

epronovost wrote:
How is that even an argument? Being skillful implies that you are great at avoiding detection "standing in the open" isn't being good at avoiding detection. It's the opposite of that. Space Marine see in pitch darkness. Standing in the shadows is basically standing in the open. This scene is simply terrible at describing any sort of stealth skill or it implies Marines don't see in the dark neither with their eyes and neither with their equipment.

So standing completely in the open, as you put it, yet being completely unseen by people who have natural night vision isn't skill. Mk. Whatever my dude.

That's because of a terrible writer who probably forgot that Space Marines could see in the dark. It's just plain bad writing. You might like it and not care for it, but it's still terrible writing. That scene is basically "worfing" on easy mode (and worfing is already a lazy way to establish skills or threat level). You can't stand in the open and not be seen by people who are just a little bit attentive or not brain dead. It's not skill to do literally nothing to be stealthy and not get noticed. It's basically incredible incompetence from the other party at best. At that point, GW could have went just an extra mile and declare that all Space Marines are mildly magical and that their power varies from Chapter to Chapter. The Raven Guard magical ability is to turn invisible in darkness or dense shadows. Of course that would require all of them to be psykers and anti-psyker technique would work to counter it or even make them easy to spot. They did no such thing so managed to avoid an easy cop-out built in any science-fantasy universe.

Meh, the power fantasy of space marines just gets elevated as childhood fans of 40k become the new custodians of the lore, pushing it to a more and more flanderised absurdity.

So long as it's a positive adjective, marines have it. Even if its ostensibly contradictory. Why? Because an author decided to write it that way.

And if we're deciding that if something was written that way then it must be true so long as it makes marines look good, then I suppose it's canon that terminators can backflip because CS Goto wrote that they could...

I don't think Astartes need to be particularly stealthy. Based on their enhanced senses, they could work better on avoidance, and while that may sound similar, they're probably not just crouching behind boxes and through air vents, but avoiding areas with active guardsmen, taking out a guard before they can react because of their enhanced reflexes. They could go to areas in which guard start to slack because the news of space marines came a month ago, and there's been no sightings. And then, once they're in, murderhobo their way to victory.

 TheBestBucketHead wrote:
I don't think Astartes need to be particularly stealthy. Based on their enhanced senses, they could work better on avoidance, and while that may sound similar, they're probably not just crouching behind boxes and through air vents, but avoiding areas with active guardsmen, taking out a guard before they can react because of their enhanced reflexes. They could go to areas in which guard start to slack because the news of space marines came a month ago, and there's been no sightings. And then, once they're in, murderhobo their way to victory.

exactly. it's like the case of rarely seeing a wild animal because by time you'd see them they've already seen/heard/smelt you and vamoosed.

Seems like a big armored super human would be better suited to setting ambushes. Finding a place you expect the target to come to, settling into a hidey hole with some camo and letting your suits support systems and discipline let you stay in place until the target comes by.

Then again, corax was noted to have a physic ability to be sorta invisible, as did a small number of the space marines in his legion. The thousand sons also used some pretty powerful not magic to infiltrate, like having magnus, that huge sod, look like a regular old marine.

But in most situations, if you wanted one person to get into a secure location and kill another person, the inquisition and the assassins would be a better choice surely?

Then again, the real question is. If you can teleport a bunch of terminators into a bunker to kill the command structure, why in the world can you just stick a bomb on said teleporter platform to do the job for a fraction of the investment. Besides of course, space monks and code of honour type stuff.

cody.d. wrote:
Seems like a big armored super human would be better suited to setting ambushes. Finding a place you expect the target to come to, settling into a hidey hole with some camo and letting your suits support systems and discipline let you stay in place until the target comes by.

Then again, corax was noted to have a physic ability to be sorta invisible, as did a small number of the space marines in his legion. The thousand sons also used some pretty powerful not magic to infiltrate, like having magnus, that huge sod, look like a regular old marine.

But in most situations, if you wanted one person to get into a secure location and kill another person, the inquisition and the assassins would be a better choice surely?

Then again, the real question is. If you can teleport a bunch of terminators into a bunker to kill the command structure, why in the world can you just stick a bomb on said teleporter platform to do the job for a fraction of the investment. Besides of course, space monks and code of honour type stuff.

Because the problem with a bomb is they're imprecise. it'll blow up the room, deal a whole ton of damage and confirming if you blew your target into such small chunks there's no body left to Identify, or if he ducked out to take a dump and you missed him entirely. It also means no chance of salvaging any information, or holding the command bunker for your own use.

cody.d. wrote:
Then again, the real question is. If you can teleport a bunch of terminators into a bunker to kill the command structure, why in the world can you just stick a bomb on said teleporter platform to do the job for a fraction of the investment. Besides of course, space monks and code of honour type stuff.

It's actually a bigger investment. a bomb is one use only. The teleported Terminators, if they survive, and they almost certainly will, can be used again and again and again. It's much easier. Plus if what you need taken is a fortress or bunker complex, once you have troops inside you can seize the thing pretty easily, especially if they are Terminators and with relatively mild damage. If you want a to teleport a bomb you would need some sort of tactical nuke to take out the bunker complex from the inside and lose the real estate at the same time.

I was under the impression from the small number of Raven Guard stories I've read that their stealth was mildly supernatural in nature. Sort of like striking scorpions'/Karandras's stealth. It's mostly actual skill, but the rules of the setting cause that skill to boil over into literal supernatural invisibility, at least sometimes. Isn't that what RG mean when they refer to "wraith slipping"?

In D&D terms, Astartes take a Size penalty to their Stealth checks, but they also have a bunch of ranks in Stealth, probably have a really high Dexterity stat, and probably have some modifiers from their equipment (sound bafflers in their armour, etc.) So while their physiques don't help with stealth, and while marine swearing their parade colors instead of a camo pattern are even worse off, they're offsetting their drawbacks with other modifiers.

In general, I don't think astartes stealth works quite the same way normal human stealth does. Someone pointed out their enhanced senses allowing them to realize that they need to round a corner or go to ground sooner than a normal human would. Their superhuman anatomy also probably opens up routes that wouldn't be possible for normal humans. Sure, the enemy in the castle are watching the skies and all the conventional land approaches and maybe even the sewer system. But they might not be expecting anyone to climb the several miles high sheer cliff face right behind the castle. Astartes can jump gaps and climb surfaces most opponents couldn't. They can slow their bodily functions sufficiently to not register on bioscanners if they get carried through certain scanners or simply go perfectly still in a way that most humans can't. They can quickly and (relatively) quietly kill the combat servitors you put in the sewers, expecting any scuffle against such guardians to result in a raised alarm. They can even eat your brains to learn what the new patrol route you went over in your morning meeting look like.

Basically, marines have a lot of tools and options that most would-be ninjas don't.

I see no reason why Astartes can't be stealthy. Yes they are big and wear armour, but the setting is science fantasy and much of that can be hand-waved away. When it comes to things like Reivers and what not, the armour has noise dampeners/baffles etc to keep it very quiet if I'm not mistaken.

Also, being Space Marines, they are often fighting in vacuum, so sound is not a concern (of course vibrations will still travel through solid materials...)

In general, Astartes stealth reminds me of this Liam Neeson quote from Batman Begins:

A Ninja understands that invisibility is a matter of patience -- and agility.

Two things Astartes have in abundance.

With regard to Raven Guard, yes, I think there is a bit of space magic going on there, but a bit like Faith in 40k, it is poorly defined, and doesn't seem to be a psychic power in the usual sense. It very much seems to be in line with the sort of magic hobbits have in LOTR:

There is little or no magic about them, except the ordinary everyday sort which helps them to disappear quietly and quickly when large stupid folk like you and me come blundering along, making a noise like elephants which they can hear a mile off

There is some seriously profound fan-boys in this thread. It is actually comical. No, 8 ft tall people in POWER ARMOR cannot sneak very well, Raven Guard or not. The post I have been reading are just baffling. Has the marine fanbase really gotten here?

Anyhow. Its like the Alpha Legion. A clandestine chapter whom focus's on asymmetrical warfare.
The Alpha legion does not use its marines to infiltrate or stealth or any nonsense on offer here. They have human operatives for that. The reason they are so dangerous is because they DO NOT fight like marines.

I would imagine the Raven Guard to be much of the same. Not actually stealthy but uses tactics that are not on offer from other chapters.

Table wrote:
There is some seriously profound fan-boys in this thread. It is actually comical. No, 8 ft tall people in POWER ARMOR cannot sneak very well, Raven Guard or not. The post I have been reading are just baffling. Has the marine fanbase really gotten here?

Anyhow. Its like the Alpha Legion. A clandestine chapter whom focus's on asymmetrical warfare.
The Alpha legion does not use its marines to infiltrate or stealth or any nonsense on offer here. They have human operatives for that. The reason they are so dangerous is because they DO NOT fight like marines.

I would imagine the Raven Guard to be much of the same. Not actually stealthy but uses tactics that are not on offer from other chapters.

The Alpha Legion has a fairly cool concept, but when you think about it it's also very stupid. It's the Legion of Space Marines that is awesome at having very good human servants who do all the hard job of infiltration and sabotage. You could basically cut the Space Marines from the Alpha Legion and make it the 40K universe version of Hydra in Marvel.

Let me clarify my statement from earlier. Astartes would absolutely be worse at stealth as a similarly or even worse train human, and that is because of their size. However, people are underplaying how their senses would help, and that's what my comment was for. They'd absolutely be better setting ambushes, finding intruders, or just cutting off the head when the guard storms the base. But that does not mean they'd be useless. Taking out the lights at night, taking out guardsmen who were slacking, avoiding populated areas, and knowing when someone might turn the corner are all how they would act. They might even be able to eat a guy's brain or something for info if they need it. They just have to work to their advantages and not disadvantages. I think the assumption for the anti crowd here is that stealth means hiding behind things in the room. It can, but it more broadly means avoiding being spotted, which they can do, just not as well as a guardsman or ratling.

Also, Alpharius broke into the Golden Palace, sneaking by Custodes. I'm not saying it was well written, but it happened.

epronovost wrote:

Table wrote:
There is some seriously profound fan-boys in this thread. It is actually comical. No, 8 ft tall people in POWER ARMOR cannot sneak very well, Raven Guard or not. The post I have been reading are just baffling. Has the marine fanbase really gotten here?

Anyhow. Its like the Alpha Legion. A clandestine chapter whom focus's on asymmetrical warfare.
The Alpha legion does not use its marines to infiltrate or stealth or any nonsense on offer here. They have human operatives for that. The reason they are so dangerous is because they DO NOT fight like marines.

I would imagine the Raven Guard to be much of the same. Not actually stealthy but uses tactics that are not on offer from other chapters.

The Alpha Legion has a fairly cool concept, but when you think about it it's also very stupid. It's the Legion of Space Marines that is awesome at having very good human servants who do all the hard job of infiltration and sabotage. You could basically cut the Space Marines from the Alpha Legion and make it the 40K universe version of Hydra in Marvel.

Oh, they're absolutely the 40k version of Hydra. Possibly literally inspired by given the literal hydra motif.

But I think you may be selling the marines a bit short. There's a scene in Sons of the Hydra(?) where they need to sneak into an inquisitorial base. So they do something like...
* Walk around in an unbreathable environment.
* Bury themselves underground along a route they know a transport will be passing.
* Wait for the krak grenade boobytrap they rigged to go off and make the imperials pause to check the damage.
* Grab onto the underside of the transport and let it carry them into the base.

I'm probably misremembering that somewhat, but that scene alone demonstrates the marines utilizing infiltration options that a normal human probably couldn't pull off. A normal human wouldn't be able to walk around in the unbreathable environment without some non-standard gear. The astartes rely on their gear here, sure, but only on features that seem to be pretty standard power armor stuff. Burying themselves without specialized tools, remaining underground for an extended period of time, and then unburying themselves fast enough to hitch a ride seems like it would probably be beyond an unaugmented human. And even hanging onto the underside of a tank for an extended period of time over unpaved ground seems like a pretty big ask for a human. And that's just one scene.

I'm not downplaying the stealth skills of non-marines. Just trying to point out that an astartes' physiology isn't all downsides when it comes to sneaking around. Are you easier to spot than a guardsman? Sure. But in exchange for being easier to spot, you can jump and climb places the guardsman can't. And you can do that jumping and climbing while having the benefits of your helmet's advanced auspex and not needing to breathe for extended periods of time.

Wyldhunt wrote:
I'm probably misremembering that somewhat, but that scene alone demonstrates the marines utilizing infiltration options that a normal human probably couldn't pull off. A normal human wouldn't be able to walk around in the unbreathable environment without some non-standard gear. The astartes rely on their gear here, sure, but only on features that seem to be pretty standard power armor stuff. Burying themselves without specialized tools, remaining underground for an extended period of time, and then unburying themselves fast enough to hitch a ride seems like it would probably be beyond an unaugmented human. And even hanging onto the underside of a tank for an extended period of time over unpaved ground seems like a pretty big ask for a human. And that's just one scene.

Again that's a bit of a shaky, but at least believable at face value writing. It has several big weaknesses. First breathing apparatus is pretty much a standard piece of equipment for many guardsmen. Hell it's necessary for many to operate on the surface of their own planet because it's too toxic to breath like on many places in Armageddon. It's also standard mandatory gear on all Scions. Burying yourself is a nice trick, but it takes time and you have to dispose of the earth you moved and have to be careful else someone might find it suspicious that there are mounds of earth where there used to be none, especially mounts of earth appropriate for a 7 to 8 foot tall Space Marines in armor. A Space Marine in armor is at least two to three feet thick, maybe more with the power pack. Then bursting out of the ground to catch a ride under a truck is a fancy one, but not very much stealthy since you are moving a lot of ground still, but if you are perfectly positioned, you could pull it off. Finally there is the little strangeness of latching under a tank which normally have a quite low ground clearance and Space Marines in armor being both very heavy and extra "thiccc" due to their physique and imposing armor set. Plus, such an extra weight would probably be noticed by the driver of the vehicle. You don't add close to a 500 kilos under your vehicle without noticing something and you need something rather sturdy to support that weight without breaking but I'll be generous enough to grant it to mag boots and gauntlets. I think this is a very neat trick and at least shows a writer trying to come off with a clever infiltration plan but it would work better with humans or human sized superhuman without heavy armor like assassins for example.

Ok so an Astartes to make use of "alternative stealth" they need to use to the limit all off their fancy equipment and transhuman bodies... Instead of a regular human just doing standard stealth techniques???

What a brilliant confirmation that astartes are indeed like that joke NASA space pen.

Skill at stealth is all about knowing how to use the environment to conceal yourself.
You can't just render yourself invisible when standing in front of someone by being really good.

Situations like a Ravenguard hiding in the shadows right next to someone are ridiculous, and are basically authors trying to emphasise how great at stealth someone is without the skills to express that more logically.

This sort of thing happened constantly when I was reading "Legion" (about the Alpha Legion). Except there it's even worse because they're in blue/green armour!

Also, with regards to Marines having enhanced senses either due to their biology or their armour which would help them, the only chapter which was ever given any representation of that, I believe, was the Space Wolves (surprise, surprise) who had the acute senses perk.

Space Marines never got the Night Vision USR or even had access to it through wargear, unlike other races. Indeed, if space marines could all see in the dark, why did they attach searchlights to their vehicles?

Also, any force with thermal imaging could instantly spot Space Marines running around in their power armour, no matter how stealthy they are trying to be, because said power armour is powered by a nuclear reactor which puts out a lot of heat, and you cannot stop it from doing that without ending up with a meltdown or a cooked marine or both. A marine burying itself would quickly cook itself and die due to the heat output of the reactor they have strapped to their back.

 A Town Called Malus wrote:
Also, with regards to Marines having enhanced senses either due to their biology or their armour which would help them, the only chapter which was ever given any representation of that, I believe, was the Space Wolves (surprise, surprise) who had the acute senses perk.

Space Marines never got the Night Vision USR or even had access to it through wargear, unlike other races.

Also, any force with thermal imaging could instantly spot Space Marines running around in their power armour, no matter how stealthy they are trying to be, because said power armour is powered by a nuclear reactor which puts out a lot of heat, and you cannot stop it from doing that without ending up with a meltdown or a cooked marine or both. A marine burying itself would quickly cook itself and die due to the heat output of the reactor they have strapped to their back.

can you name a single time in which heat from marine armor reactors has even come up, at all? Cause I sure can't.
40k is set nearly 40,000 years into the future, if waste heat being a problem has NEVER come up, AT ALL, we can proably assume it's simply not an issue with the technology they're using.

BrianDavion wrote:

 A Town Called Malus wrote:
Also, with regards to Marines having enhanced senses either due to their biology or their armour which would help them, the only chapter which was ever given any representation of that, I believe, was the Space Wolves (surprise, surprise) who had the acute senses perk.

Space Marines never got the Night Vision USR or even had access to it through wargear, unlike other races.

Also, any force with thermal imaging could instantly spot Space Marines running around in their power armour, no matter how stealthy they are trying to be, because said power armour is powered by a nuclear reactor which puts out a lot of heat, and you cannot stop it from doing that without ending up with a meltdown or a cooked marine or both. A marine burying itself would quickly cook itself and die due to the heat output of the reactor they have strapped to their back.

can you name a single time in which heat from marine armor reactors has even come up, at all? Cause I sure can't.
40k is set nearly 40,000 years into the future, if waste heat being a problem has NEVER come up, AT ALL, we can proably assume it's simply not an issue with the technology they're using.

Sure. Look at the backpack of a marine model and at the vents on the bottom of their backpack. That is where the heat of their power generator is vented to the outside. It generates enough heat that it requires a dedicated system to vent said heat out of the armour system. From the size of the vents we can also tell that the maximum capacity of said venting system is limited, which puts a cap on how hot the reactor can run before it isn't able to vent the heat sufficiently fast to prevent the reactor from overheating and meltdown. This is also limited by the environmental conditions as the vents make clear that the system operates via transferring the energy to the outside atmosphere, it uses the atmosphere as the heat dump. A Marine reactor will be less efficient on a hot planet than a cold one, for example. It will also be incredibly dangerous to operate in a vacuum where the only method of passive heat loss is radiation unless the armour is using its own air supply as a heat dump then venting it into space.

The laws of thermodynamics state that you cannot have a 100% efficient conversion of energy to work. There will always be wastage and the level of wastage is typically extremely high if you want your system to be able to do work fast.

 A Town Called Malus wrote:

BrianDavion wrote:

 A Town Called Malus wrote:
Also, with regards to Marines having enhanced senses either due to their biology or their armour which would help them, the only chapter which was ever given any representation of that, I believe, was the Space Wolves (surprise, surprise) who had the acute senses perk.

Space Marines never got the Night Vision USR or even had access to it through wargear, unlike other races.

Also, any force with thermal imaging could instantly spot Space Marines running around in their power armour, no matter how stealthy they are trying to be, because said power armour is powered by a nuclear reactor which puts out a lot of heat, and you cannot stop it from doing that without ending up with a meltdown or a cooked marine or both. A marine burying itself would quickly cook itself and die due to the heat output of the reactor they have strapped to their back.

can you name a single time in which heat from marine armor reactors has even come up, at all? Cause I sure can't.
40k is set nearly 40,000 years into the future, if waste heat being a problem has NEVER come up, AT ALL, we can proably assume it's simply not an issue with the technology they're using.

Sure. Look at the backpack of a marine model and at the two vents on their backpack. That is where the heat of their power generator is vented to the outside.

Those aren’t vents, they are stabilising jets for use in low gravity:

https://www.warhammer-community.com/2016/10/30/the-anatomy-of-power-armour/

A marine backpack actually has 6-9 vents, depending on what you count various bits at and which sculpts you look at. Presumably some of those will be air intakes though and maybe others for stuff like the air filtration system and stuff.

There's a lot of real world considerations that don't come up in the lore though, like where the hell does a Space Marine keep all this ammo. They're just handwaved for the sake of the story and aesthetics.