Throughout the Stygian Wars Alpha Legion forces supplied hidden cults in the Imperium with so called "Doom Devices" often explosives of Impressive power there were other variations. Some contained chemical or biological agents that would taint a wide area. One in particular was able to trigger latent psychers within a 100 miles of the device. Shortly after that device was used massive warp incursion devastated the planet. With the use of "Doom Devices" Alpha legion forces were able to devastate large swathes behind Imperial lines.