'After the fact' traitors?

[Valkyrion]

Are there any details of loyalists turned traitor after the heresy has begun but before the siege?

I know the White Scars had a traitor contingent because of the lodges, but I mean more like a company of Ultramarines or Imperial Fists going rogue simply because they believed in Horus' premise, or believed that the traitors would win, or just to spite their primarch or whatever.

Anything out there to this effect?

[Noserenda]

I think they mention some shattered legion forces flip sides in their black book? 

Technically all the blackshields too i guess.

[LameBeard]

So we aren’t counting all the Space Wolves doing what Horus wanted and piling in on Prospero? Like Banksy says, it’s not rebellion you should fear, it’s blind obedience.

 

And shenanigans on Caliban. This was not exactly the arc I enjoyed the most of those I’ve read in the HH series, but I do like that the authors were brave enough to make Lion El Johnson a, shall we say, less-than-sympathetic character, and that then creates some room for Dark Angels to go, hmmm, maybe I don’t want to be following him.

[Valkyrion]

2 hours ago, LameBeard said:

So we aren’t counting all the Space Wolves doing what Horus wanted and piling in on Prospero? Like Banksy says, it’s not rebellion you should fear, it’s blind obedience.

 

And shenanigans on Caliban. This was not exactly the arc I enjoyed the most of those I’ve read in the HH series, but I do like that the authors were brave enough to make Lion El Johnson a, shall we say, less-than-sympathetic character, and that then creates some room for Dark Angels to go, hmmm, maybe I don’t want to be following him.

 

Those things happened before the heresy at large - I'm looking for examples of loyalists choosing to betray their legion because Horus has already declared. 

[LameBeard]

What about the disaffected, Terran, pro-Horus Ravenguard? Was that just hinted at, or did we get a story of their defection?

[Lord_Caerolion]

There was an apparently not-insignificant number of Iron Hands who threw in with Horus after the Massacre, following their “might makes right” philosophy. 

[Cactus]

18 hours ago, LameBeard said:

What about the disaffected, Terran, pro-Horus Ravenguard? Was that just hinted at, or did we get a story of their defection?

As I recall there was a mysterious silent Raven Guard traitor in the background of one or two novels. Nothing more ever came of it.

[2PlusEasy]

There may not be too many obvious examples unfortunately. The White Scars who were declared Saygan Mazan are one example.

 

Some of the actions of the Shattered Legions / Blackshields and the collateral damage they caused leaves alot for questioning though. Autek Mor and the Iron Hands who eventually became the Red Talons successor chapter for example. The Ashen Claws as well. Even the (alleged) Carcharodons.

 

I think the main weakness of the loyalists wasn't from defections, but from a lack of unison. The Dark Angels were content to fight their own war and answer to noone. Guiliman essentially wrote Terra off with Imperium Secondus until it was obvious Terra hadn't fallen. The shattered Legions went rogue in many cases, or were so drastically mauled that they couldn't really contribute. And let's not get started about how silly the Space Wolves were, being too blindingly obedient then later obnoxiously belligerent.

Edited March 31 by 2PlusEasy

[Pacific81]

This sort of thing is always a tricky one as, apart from mention of the Iron Warriors being used like a tool on the most awful battlefields and then discarded afterwards, even after 50+ books the MO of most of the traitors unfortunately still falls back on "a wizard did it". Horus was stabbed by a magic (bad) sword, then turned against the big E. Most that followed him did so because he was Warmaster or because Chaos had spoken to them. So by extension, with a few exceptions, the loyalist legions were not as vulnerable to the whispers of Chaos then they didn't turn - and we haven't got that philosophical underpinning of a reason some of them might have decided Horus had the better plan (other than the aforementioned Iron Warriors). 

 

You can actually extend this to most of 40k lore, where despite the horribly dystopian setting, the only time you really read of rebellion is either a) Chaos cult b) Genestealer uprising (as fore-runner of a 'Nid invasion). You don't ever read about hive workers deciding that they don't want to live out their lives without seeing the sun, or a Guard regiment deciding it doesn't want to run into enemy guns. Day of Ascension by Adrian Tchaikovsky is an exception to the rule (notably an author 'outside' of the BL stable, who has done some work for them) with at least giving some underpinnings to the crappy lives the downtrodden live on hive worlds. It's obviously still do with the 'Stealer cults, but there is at least some rational cause/effect there, beyond a wizard doing something. 

[Interrogator Stobz]

That's a pretty tight timeline for derails, relatively speaking of course.