The Cloaking Array was an archeotech device deployed by some Imperial and Traitor forces during the Great Crusade and Horus Heresy eras. This relic generated a highly-localised refraction field that distorted light and many other forms of electromagnetic radiation in such a way as to render the bearer invisible to the naked eye and most forms of machine sensor.
The Great Crusade came in the wake of the Age of Strife, a long and terrible era during which Mankind unleashed and was laid low by weapons of star-razing destructive power and genocidal scope, many born during the preceding Age of Technology.
When the Emperor's crusading forces pushed back the darkness that had fallen upon the worlds of Mankind, evidence of the ancient and terrible artefacts were found and studied by the tech-savants of the Mechanicum, who coveted them greatly.
Occasionally, one of these examples of ancient archaeotech would be recovered and taken up by the heroes of the Great Crusade itself, becoming a potent relic, its name and legend as widespread and celebrated as the Crusaders who bore it into battle.
As the Great Crusade continued ever onwards, multiple examples of some types of relic were encountered and great effort was committed to cataloguing their class, understanding their nature and replicating their function. Often the Mechanicum could fathom the basic technology underpinning a relic, but could not create a functioning copy.
Nonetheless, the effort to decode the ancient technological foundation of such artefacts continued, with other discoveries made in the process expanding the canon of the Machine God exponentially.
- The Horus Heresy - Book Four: Conquest (Forge World Series) by Alan Bligh, pp. 222-223