Warp-Drive

Warp-Drives, or Warp-Engines, are devices used by many races to actually enter the warp, a parallel or alternate dimension to that of real space, for effective faster than light travel. They are huge and bulky devices needing large ships to carry. Ships fitted with warp drives are known as Warp-Ships or Warp-Capable Craft. Warp drives allow ships to enter the warp and bypass light years of real space in a relatively short time, although the dangers associated with all warp travel are terrible indeed.

Gellar Field
All Imperial warp-capable craft possess a module attached to the warp drive which emits a force field called a Gellar Field. The Gellar Field creates a 'bubble of real space' around the ship.

The Gellar field protects the ship and its occupants from the hostility of the warp itself, as well as from the predation of warp entities, such as daemons, as it travels through the warp, as a Daemon cannot enter or even survive the Materium except under very precise conditions.

The weakening, failure, and collapse of a Gellar Field while the ship is traveling through the warp would be completely disastrous. Warp entities would tear the ship apart to reach and consume the souls of the crew.