A Flare Shield was a directional electromagnetic flux field generator, similar in function to Imperial Void Shields, that was used by the Mechanicum of Mars and other Imperial military forces during the Great Crusade and Horus Heresy. The workings of Flare Shields were only truly understood by the Mechanicum's highest-ranked Magi and other Adepts, and the technology was believed to be a product of the Dark Age of Technology that originated from a source best left forgotten. Flare Shields lacked the defensive power of the much larger Void Shields that are used by Titans and Imperial warships, yet were capable of deflecting or dispersing glancing or diffuse impacts and shrapnel as well as reducing the potency of more focused strikes. The main advantage that Flare Shields possessed over the more powerful Void Shields was that they could be mounted on much smaller vehicles, so long as the vehicle was also equipped with rapid cycling plasma or fusion reactors of sufficient power. Flare Shields were found on Mechanicum vehicles such as the Jocasta Pattern Grav-attack vehicle and certain classes of Knight walkers, as well as on the Spartan Assault Tank, Malcador Heavy Tank, Thunderhawk Gunship, and Thunderhawk Transporter of the Legiones Astartes. It is unknown if the Adeptus Mechanicus is able to produce Flare Shield technology in the late 41st Millennium or if the technology has been lost to the Imperium like so much else from the Great Crusade era.
- Horus Heresy - Book One: Betrayal by Alan Bligh, pp. 222, 226-227, 239