Board Thread:Warhammer 40k General Discussion/@comment-87.104.181.191-20160131190756/@comment-26516936-20160208094959

Thats very true of the Dark Angels every one of their 2nd foundation chapters secretly acknowledge the that the leader of the Dark Angels is the master of all of them & will answer his call at any time without question & even though the Dark Angels wasn't a large legion there would probably would haven been at least 2 dozen second foundation chapters. So when Lion el'Jonson returns he will have a sizeable force of at least 20,000 astartes to call on immediately. Though the Ultramarines spawned far more chapters than the the Dark Angels they lack the secret cohesiveness of the Dark Angel Chapters & it would take Gulliman much longer to assemble them into a cohesive whole.

So If you count all the Dark Angel second foundation chapters together then the Dark Angels are the largest, if you don't then it probably does come down to either the Black Templars or the Space Wolves. Which of those two is the larger would be a guess as neither (especially the Space Wolves) are compliant with Guillimans directives. The Space Wolves never split so would have numbered 20 - 30 thousand post heresy but they have beens whittled down savagely in the 10,000 years since but still probably number at least a few thousand (maybe more now with the return of the 13th). As for the Black Templars they are so widely spread it's possible even they don't know their exact numbers but the total of around 5 - 6 thousand has been widely theorised.

Of course that only takes into account the loyalist forces if we include the chaos legions then it comes down to either the Black Legion, The Crimson Corsairs or maybe even the Alpha Legion, no one (save perhaps Alpharius/Omegon) has any idea how many of the Alpha Legion there actually is. Of the others the Word Bearers & Iron Warriors still have good numbers but probably less than at least the Black Legion & the Crimson Corsairs, While the Thousand Sons, World Eaters & Emperors Children have been virtually destroyed with none of them totalling more than a few thousand legionaries each. The Death Guard would number more but not many more (they have had few - if any - replacements since the heresy). The Night Lords might have numbers similer to the Word Bearers & Iron Warriors but were - until recently - scattered & leaderless & most of them while enemies of the Empire are not true servants of chaos.