It was never the intention that the Wolves were being sent out as assassins; they were never "expected to be able to kill the Primarchs". It seems that there are some mistaken assumptions being made here, so let me explain.
After Magnus breaks the Nikaea edict, Malcador orders Russ to send a small contingent of Wolves out to each of the other primarchs. Their primary mission is to observe those primarchs and report back on any behaviour that might show sympathy to Magnus or anything that smacks of similar rebellion. Note that this is Malcador who gives the order, not the Emperor. At this point, the Emperor still trusts his sons; but the Sigillite doesn't trust anyone.
The Wolf "observers" (and Russ) know full well that this is potentially a suicide mission, because if any of the primarchs have turned, they could be killed on arrival or not long after - but if that happens, Russ and Malcador will know something is rotten when they don't report back at the appointed time. The Wolves know that if they find a primarch who has gone bad, their mission is to A) send a warning and B) try to kill him.
None of the Wolves have any illusions about the fact that they will all die if they draw their weapons against a primarch; the SW captain Helik Redknife says exactly that in FTT. Even as "the Emperor's Executioners", the best they could possibly do would be to wound a primarch, perhaps slow him down. They know this going in, but they accept this duty because they are the Wolves of Russ and they do as he commands them.
So why send the Wolves instead of the Custodians?
First, it's a simple question of logistics. There are simply more Wolves than there are Custodians, and the Wolves are scattered out in the galaxy already at large, closer to the primarchs on the Great Crusade, whereas the Custodians are largely centred on Terra. It's just quicker and easier to re-task Space Wolf elements to hook up with the primarchs than to send out Custodians "the long way round".
And of course, not all of those Space Wolf squads will actually be able to fulfil their mission. Some won't be able to find the primarchs they are sent to observe, others will be killed as the heresy kicks off. Malcador will find out the hard way that his plan is too little, too late.
Secondly, if the intent was just to send out teams capable of killing a primarch, you'd need at least two Custodians to do the deed, probably three to be certain. That means sending more than fifty Custodians out into the galaxy, away from the actual job they are trained for and assigned to do, which is to protect the Emperor. Don't forget, the Custodians are a defensive army, not typically assigned to pro-active missions. Considering that some Custodians will already be leaving Terra to join the Wolves at the punishment of Prospero, do you really think that the Custodian Guard would accept an order from Malcador to leave their master with an even more reduced protection detail, especially at a time when one of his sons has just turned renegade and psionically invaded the Imperial Palace? Doesn't seem likely to me; not to mention the fact that the Custodians take their commands from the Emperor, not Malcador. The Sigillite doesn't actually have the right to give them that order.
The Wolves get the mission because they are the best tool for the job, in the right place at the right time, because they do the deeds that no others will accept, without question; and because, pragmatically speaking, Malcador sees them as disposable.
Originally Posted by JMSwallow
Hey, a question about Fear To Tread...
