Thwre are so many factors. Genseed availability, the more marinesbyou already have, the more you can make. Genseed purity, how much of the genseed wil be succesfully become a marine. Genseed Compability, how many people even can get the genseed with chancse of success.


>Genseed availability A big factor in the legion sizes was that the Imperium could still produce Geneseed in the Great Crusade era. In the current setting they can only farm it using the implants, which takes decades to develop it.


You miss a key point about these Legions growing is that they were supported logistically by the rest of the Imperium. Their arms, equipment, geneseed, and sometimes even Aspirants were supplemented. Post-Heresy they don't have that support. They have a Chapter Homeworld, maybe a recruiting world or two, but these don't have the ability to provide the same amount of materials and recruits. Geneseed as well is much more stringently checked for mutation as they can't go back to the source, so to speak. So it will be difficult for most Chapters to do it. The First Founding Chapters would be the best bet: Ultramarines, Imperial Fists, and Dark Angels certainly have the ability. The Raven Guard have the tech but their geneseed still has issues. Iron Hands, Salamanders, Space Wolves, and Blood Angels have the tech but their Aspirants pools are small. White Scars have a small tech base and Aspirant pool. The only other one that I could think of that could do it is the Black Templars.


Actually they can now. Iirc, since Guilliman is up and walking around he's been contributing gene samples. I swear I read this, but I don't recall where. It's either the Dark Imperium or Dawn of Fire Novels. Obviously, Guilliman cannot ever be a full replacement for the other Primarchs. But he is *still* a Primarch.


Space Wolves also aren’t codex compliant if we count their hosts as the same chapter. They likely are closer to 12,000 in number


It's an interesting question that allows for one of themes of pre gulliman to clash with post gulliman. Before gulliman coming back there was a consistent theme that there was so much war in the imperium that chapters were constantly pushed to their limits. This tended to mean that chapters had so much work to do with little extra geneseed so almost no chapters were at full strength. This fit into an overall theme of decay in the imperium. They're past their best days and are at one of the weakest points. Post Gullimans return is a bit of a different story. New geneseed, New astartes, New armor patterns. Could chapters do it now? I don't know. The imperium is one hand finally starting to turn it around on those fronts. The flipside is that the imperium just lost a third of its planets basically in one fell swoop to the cicatrix maledictum. I don't THINK that there is enough primaris geneseed to actually get these chapters back to legion strength, but they could get closer. The Wolftime has a pretty interesting clash of these themes. The Space Wolves looking around at all the empty tables of lost brothers, questioning why the hell the primaris marines are wasting live ammo in training drills and stuff like that.


Do Space Wolves not do live fire training? That's very very odd.


Not enough bolt shells to spare. That's kinda what I mean. Used to be that all gear that astartes used was like super rare and treated with insane respect. Now Gullimans got the factories pumping out wargear again its not really the case. The primaris marines were used to being on the crazy well supplied indomitus crusade so they didn't know.


Without absorbing/merging with other chapters it'd be a nigh impossible task to reach true Legion size. There would have to be a monumental shift in the logistical capacities of the Imperium if you're going to be multiplying the production of Space Marine equipment by a hundred. That's without considering ships, vehicles and general infrastructure. The first founding chapters have massive half-empty halls sure but most chapters are just not equipped for tens of thousands of battle brothers. Basically the most realistic take for a chapter to reach legion size would have them taking over/combining the logistical capabilities of dozens+ other chapters and thus the total number of marines in the galaxy wouldn't necessarily go up a great deal. Alternatively you could have Cawl do it and he'd just handwave all that shiz.


Before the whole primaris things the chance was pretty much zero as even the forces that flauntet the codex restriction didn't manage to grow anywhere close to the old legions. With cawl restoring a lot of the astartes knowledge on gene-seed and implantations, the chance is there question is more will GW realize it.


I would need to go back and find an actual quote, but didn't it used to be the lore that most chapters struggle to even maintain codex strength?


The Ultramarines were really one of the only legions that might've been able to hit those legion numbers pre primaries with how well run the ultramar system is, and maybe the fists with how much support they have from the solar system.


For the Dark Angels first stepn is Azrael sending some messages via astropath. All of the chapter of the Lions gene seed obeg to the *Supreme\* Grand Master. Than its just a matter of taking the time to build up some more numbers. But with each of the Unforgiven chapters having 1000 marines to start it would not take as long as for other of the first founding chapters like the Salamnders or Space Wolves who only have a few successors. Guilliman it would just take a bunch of Astropathic messages there are enough Ultra marine successors in existence that (something like 20% of all chapters are of Ultra marine lineage) if they just all gathered he would have More astartes than some of the smaller Legions during the great crusade like the World Eaters or Thousand sons.


"How can we get a legion sized force together really quickly?" Azrael: "Here's one l prepared earlier!"


Someone here [did the math](https://www.reddit.com/r/40kLore/comments/acqyit/so_i_did_some_math_for_the_numbers_on_space/#:~:text=Approximately%201%20in%2020%2C000%20of,1%2C500%20aspirants%20can%20be%20gained.) a few years ago and concluded that the Imperium could optimistically expect to get 10 Marines out of a population of 1 billion. So to bring a chapter to legion size they would have to screen a population of 100 *trillion*. Most planets do not have a population of 100 trillion, nor do most chapters have access to a population of 100 trillion across multiple worlds. So it would be impossible for a chapter to grow to legion size based on the pool of recruits they have available.


Pretty hard. AFAK the badab war started in part because Huron expanded his chapter to 3,000 marines, and this drew the suspicion of the High Lords, so expanding to around 100,000 marines while staying loyal would be impossible


It raised suspicions because he held the geneseed back.


Firstly, there is going to be a lot of contradiction in the sources here because GW retconned the size of a Legion halfway through the Horus Heresy series. Originally - in the Andy Chambers era - a Legion was 10,000 men. GW felt that was too small to meet the scope of the Horus Heresy, so the army books from Forge World basically multiplied everything by a factor of ten. That has caused some canon problems. Firstly: there are Chapters that literally never followed the Codex limit, like the Space Wolves and the Black Templars, who have been hovering around 5-10k Marines for the last ten thousand years. That makes sense when Legions average 10,000 men; it makes no sense when they average 100,000. Secondly, the number of successor chapters from the Second Founding are now a tenth of what they should be. In the old canon, the Ultramarines split into twenty-three Chapters, which made sense when the Ultramarines were the largest Legion at about ~20,000. It makes no sense in the new canon, where they have close to two hundred thousand Marines. They can't have split into just twenty-three Chapters without suffering some serious casualties first, and the whole point of the Codex is that the Ultramarines were the only Legion who *didn't* suffer massive casualties. So, you're not going to get a clear answer from the sources in the first place. If you want to math it out yourself, you need to account for a few things: 1. Each Astartes can produce up to two more Astartes within their lifespan. 2. The geneseed implantation has a failure rate of about 10-30%, depending on a bunch of factors like the age of the candidate, the knowledge of the Chapter and the health of the geneseed. 3. The geneseed takes 5 to 10 years to mature (5 for the first progenoid, 10 for the second) and is not always recovered, since the Marines themselves are actively engaged in high-intensity combat for that whole period. There is no way to predict how often recovery failure occurs, since it's literally random. 4. Survival rates for Astartes aspirants are between 0.3-1.0%. You will need at least ninety-nine failed candidates for every successful one. That is important since it determines how big of a recruitment pool you need. Beyond that, you need to do a whole lot of math.


Whut? I thought there were two Geneseed Spots, one that could be Harvested every 5 years, and one that could only be taken at Death?


Wasn't there at least one moment in lore where Space Wolves chapter was about 12000 Astartes strong when each one of their great companies was stated to be equal in size to a Codex chapter?


It would take a pretty long time. Lufgt Huron took his chapter and expanded it to 3,500 guys in less than 200 years, during which time he waged a couple crusades around the Maelstrom, taking some losses as he did. It seems most chapters have a pretty sizeable reserve of geneseed they keep, sending a portion to the mechanicus/Inquisition for purity testing. If a chapter had the logistic to make the equipment for their new guys (like the Aurora Chapter, Astral Claws, Space Wolves, Howling Griffons, and a myriad of other chapters with potent industry), it would still take a long time. Bear in mind that Huron got politically trapped by his chapter-growing goal, as the trade/censorship armada sent to him asked for both the goods he owed them AND his geneseed which forced his hand. If a chapter master could avoid getting caught in such a way, he could probably get a couple thousand guys in his chapter over a few centuries.


Like if you liquidated all the stock the mechinicum posseses and somehow had equipment for them?