Sisters of Battle are female warriors from the six Orders Militant branches of the Adepta Sororitas, an all-female sub-organization of the Ecclesiarchy, the state church of the Imperium of Man. While all Sisters of Battle belong to the Adepta Sororitas, not all Sororitas are Sisters of Battle.
Sisters of Battle are portrayed as religious fanatics with Catholic overtones and visual design. They use a type of power armor, but do not possess interface implants like Space Marines, and the armor is lighter. In gameplay terms, the Sisters are something of a cross between Space Marines and the Imperial Guard.
What later became the Adepta Sororitas began as an all-female cult called the Daughters of the Emperor, isolated on the world of San Leor and dedicated to worship of the Emperor of Man. The Ecclesiarchy discovered this cult in the 36th millennium, and the Ecclesiarch managed to recruit them for his private bodyguard. The Daughters were then renamed as the Brides of the Emperor.
The Ecclesiarch at that time was Goge Vandire, who was originally the Master of the Administratum, but had managed to usurp the Ecclesiarchy as well, gaining him two seats among the High Lords of Terra and beginning a reign of terror. The Brides of the Emperor were Vandire's most loyal servants, but as his ambition – and sanity – got completely out of hand, the Adeptus Custodes managed to convince the leader of the Brides of Vandire's corruption. The woman promptly walked into Vandire's office and decapitated him; the Brides named themselves Daughters of the Emperor once more.
The new Ecclesiarch quickly proclaimed a decree forbidding the Ecclesiarchy from having an armed force. However, as the decree literally said "men under arms", and the Ecclesiarchy still felt vulnerable, the very same Ecclesiarch formed the Daughters into a new branch of the church: the Adepta Sororitas.
Since this time, the Sisters of Battle have been the Ecclesiarchy's military force as well as the unofficial army of the Ordo Hereticus, the branch of the Inquisition dealing with internal threats such as heresy and mutation.
There are a total of six known Orders Militant:
- Order of the Bloody Rose
- Order of the Sacred Rose
- Order of Our Martyred Lady
- Order of the Ebon Chalice
- Order of the Valorous Heart
- Order of the Argent Shroud
- Order of the Sacred Rose (Soulstorm)