Sisters of Silence
- "That's their function...aside from the fact that they fight like bastards. Got the pariah gene in 'em."
- --Leman Russ, Primarch of the Space Wolves, on the Sisters of Silence
As stated, the Emperor formed this all female army at the beginning of the Great Crusade as a counter-measure against untrained psykers, which had increased at the start of the Age of Strife. To do this, the Emperor ensured that they were all pariahs, human beings with no presence in the Warp (One has to wonder though whether they had to compete with the Officio Assassinorum for recruits (though probably not seeing as the Culexus Assasains are primarily males)). As such, the psyker's abilities would have no effect on them, but would be cancelled out when they got close enough to them. In one of his odder decisions, the Emperor explicitly had the Sisters take literal vows of silence upon becoming full Sisters. They could communicate via several sign languages (including Astartes battle-sign) but would not speak a word upon completion of their training. To ensure communication between other branches of the Imperium of Man, Sisters in training would serve as communicators.
The Sisters of Silence are also consummate warriors, trained to the same levels as the Space Marine Legions and using similar wargear, such as bolters and power weapons, as well as being covered in SoB-like power armour, albeit with no armored helmet or other head protection aside the massive jaw-like collar that hides their mouths ( it's called a Gorget mate ), which leads to a lot of deaths from headshots during the burning of Prospero. As a military force they are formidable; during the Burning of Prospero they were deployed to augment the Space Wolves and the Adeptus Custodes. While this was more because the pariah gene would neutralize the Thousand Sons psyker abilities, they were more than capable of fighting with the Astartes. They would also in turn augment the Custodes, the Imperial Fists, the Blood Angels, and the White Scars during the Siege of Terra, where the pariah gene became a boon fighting the Daemons unleashed.
After the Horus Heresy
The fate of the Sisters of Silence following the Horus Heresy has not been completely documented yet. What is known is that the sisterhood was either abandoned, exiled, or betrayed by the Imperium after the internment of the Emperor on the Golden Throne, and as a result, the sisters gave up their vow of silence.
Reasonably, since people with the Pariah gene are so useful to the Imperium and so rare (occurring in less than one in a billion people), you'd think the Imperium would institute some baby-making program with members of the Sisters of Silence to boost the number of people with the Pariah gene; the Imperium's grimdark enough to do far worse, which also addresses the fact that the Pariah gene induces feelings of unease and disgust in non-blanks, making any male volunteers who aren't blanks themselves unwilling to impregnate said members (though that can be worked around with artificial insemination).
They refused to recognize the Imperium in its political form as of M32, seeing it as a corrupted simulacrum of what the Emperor actually intended, but they still acknowledge the Emperor as the focus of their loyalty. Thus, when their services are required again in the War of The Beast, they accept the calling and return to Terra, where they are granted an audience with the Emperor in his sanctum on the throne, a privilege that not even the High Lords are afforded. Just how exactly that would've worked is a mystery, given how the Emperor can presumably only communicate psychically at this point, which probably wouldn't work at all on a group of nulls.
Also, according to a GW response to a question as how to field the Sisters (and Custodes), they still exist. Now, what the Sisters of Silence actually do is up for debate. A common rumor is that they will be added into some upcoming Sisters of Battle relaunch. If so, that would be an interesting revision; on the one hand, the Sisters of Battle, despite being designated witch-hunters, are lacking in the anti-psyker department. On the other hand, the Sisters of Silence, much like the Space Marines, are big believers in the Great Crusade era of the Imperium, and likely won't mesh well with the Ecclesiarchy. Also, the Beast Arises book ends with the Sisters of Silence being wiped out while killing the Beast, meaning that (if we are interpreting correctly the hints of some supplements) it is possible the Order was reformed with entirely new members and possibly entirely new beliefs and/or traditions. So, in conclusion, the most probable work that GW can do with SoS is saying that the Adepta Sororitas in its current form can trace its origins to both the offshoots of the Daughters of the Emperor and Sisters of Silence.
UPDATE: The Wrath of Magnus ending may hint they were reformed after the War of The Beast; after all, as long as the pariah gene still exists there are always potential recruits, and someone at the Inquisition may have decided it was a good idea to have some at hand just in case.
The Gathering Storm, book 3, indicates that the Sisters were officially disbanded upon the conclusion of the Age of Apostasy in M36 (perhaps coinciding with the formation of the Sororitas) but continued to exist through secretive enclaves throughout the Imperium right up to M41. They later showed up with the Custodes on Luna to save Guilliman from being used by Magnus to mop the floor.
They were later given their own Codex and were said to have hidden away with several orders scattered through the stars and on the Black Ships. Over time, they recruited, and their numbers swelled to tens of thousands over millennia. As for their combat history, it was "conveniently" erased by Imperial authorities to keep them secret. Some were also said to have been cut off from their orders and suppressed their powers to settle down and have descendants, before they had to relocate to avoid being lynched. After Guilliman revived, he ordered them to coordinate with Terra once again and had them join the front lines with the Custodes.
|Forces of the Sisters of Silence|
|Command:||Excruciatus Cadre - Oblivion Knight-Centura|
|Troops:|| Null Maiden Cadre - Oblivion Knight Cadre |
Prosecutor Cadre - Pursuer Cadre
Seeker Cadre - Vigilator Cadre
|Vehicles:|| Grav-Rhino - Kharon Pattern Acquistor |
|Titans:||Warlord-Sinister Pattern Battle Psi-Titan|