The Daemon Slayer is an Imperial Navy Cruiser of unknown origin. The history of this vessel is completely obscured in existing Imperial records, but it is apparently the sole ship of the Daemon Slayer-class.
The Daemon Slayer can be traced back in Imperial records to the Sargot Crusade. This ship was known to have been a part of the battlefleet of Lord Karanon but all records of this time were destroyed in the Oomlak Resurgence.
The Daemon Slayer was purpose-built around a mysterious weapon called a Psychic Cannon. A hit from this weapon unleashes a blast of unknown energy that can banish any daemon back to the Warp. Tyranid Hive Ships fair no better, as a hit from this fell weapon can knock out the synaptic control of the bio-ship, disrupting its ability to receive psychic commands from the Hive Mind.
The Tech-priests of the Adeptus Mechanicus believe that some unknown human-colonised planet constructed the ship during the Age of Strife preceding the beginning of the God-Emperor's benevolent rule in the late 30th Millennium.
The construction of the Daemon Slayer may have been part of a doomed attempt by the people of that time to keep open star lanes that were infested with daemons due to the high Warp Storm activity that marked this tumultuous era.
It would be typical of the people of the period that they would turn to the sterile magic of technology for salvation rather than the light of true faith in the one, true god of Mankind.
- Battlefleet Gothic Magazine 2, "D'aynes Fighting Ships of Segmentum Tempestus - Battlefleet Bakka," pg. 38