A Reflex Shield is an ancient variant of Void Shield technology that was used by the starships of the Raven Guard Legion as a cloaking device to protect them from detection by enemy sensors and even the naked eye.
The Reflex Shield was an innovation first developed by the Mechanicum on the Forge World of Kiavahr, the world orbited by the airless moon of Deliverance which was the homeworld of the Raven Guard Legion.
A standard Void Shield worked by using the power of the Warp itself to displace incoming projectiles and directed energy attacks through gravitic manipulation. Reflex Shield technology altered the modulation of the Warp-Drive cores that powered the Shadow of the Emperor 's Void Shields, calibrating them to a much higher tolerance and also directing them inwards, so that all of the matter and energy emitted by the great warship was redirected instead.
All forms of radiation emitted by the Raven Guard's starships could be displaced, rendering them undetectable to scanning equipment. The advantages of Reflex Shield technology fitted well with the Raven Guard Primarch Corvus Corax's ethos of war, allowing Raven Guard starships to approach their targets unseen. Under the cover of their Reflex Shields, they could strike swiftly and decisively before withdrawing. The low energy requirement for the use of the technology meant that such stealth could be maintained almost indefinitely.
There was, however, a serious downside to their use. The activation of Reflex Shields significantly reduced a ship's own sensor capabilities, essentially making them half-blind. Also, by employing its Void Shield generators for the projection of Reflex Shields, a Raven Guard vessel had no defence against physical attack. It took time to switch the shield generators from one state to the other, leaving a warship vulnerable for several solar minutes with neither its cloaking field nor its energy barriers fully operational.
To the Augurs and scanning arrays of an orbital base or starships throughout a star system, the Shadow of the Emperor or any other starship activating Reflex Shield technology would seem to melt away into the stars. To the naked eye it would appear to shimmer, as the Reflex Shields engaged and reflected all visible light from the ship's surfaces, until eventually all such energy was dampened and the vessel was rendered effectively invisible to sensors and the naked eye alike.
Another problem with Reflex Shield technology, one that Corax had unsuccessfully laboured to overcome for many years, was the relatively low amount of energy emissions it could cloak. The vessel's Plasma Reactors could only be run at half-power without generating more energy than could be displaced by the Reflex Shields. Thus, when operating under the cloak provided by the technology, a Raven Guard starship had to reduce its top speed and make do with decreased sensor capabilities.
For instance, when making for a planet, the Shadow of the Emperor would not take a direct route, it being a doctrine of the XIX Legion to always approach a target indirectly. Instead it would take a circuitous, zigzagging path, using a timing and distance formula devised by the Primarch himself to maximise the damping effect of the Reflex Shields and throw off any pursuer or sensor that might somehow detect them. Corax did not believe in taking chances when it came to moving freely and unseen.
- Deliverance Lost (Novel) by Gav Thorpe, pp. 22-23, 27-28