Warp drives, or warp engines, are devices integrated into spacecraft, making them capable of a form of faster than light travel known as warp travel or warp jumping. The warp drive allows a ship to enter the warp, travelling its currents until reemerging into real space light years away from the starting point.
The drives 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, as the warp is hostile and unpredictable in the extreme, the dangers associated with all warp travel are terrible indeed.
The warp drive was invented by mankind c.M18. Prior to this, interstellar travel was limited to sub-light speeds. Travel between star systems was painfully slow, taking many generations of travel. The warp drive was one of the most revolutionary inventions in human history - what took many generations now took days. Consequently Mankind's colonisation of The Galaxy was vastly accelerated. In c.M22 further technological progress led to the creation of the human mutant warp-pilots known as Navigators. These mutants allowed warp-crafts to make longer, safer and more accurate warp jumps through the Warp, and further accelerated the galactic colonisation.
The Gellar field was invented along with the warp drive, allowing warp-capable ships and their occupants to actually survive the hostile environment of the warp. It 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.
The Gellar field device emits a field called a Gellar field, essentially creating a bubble of real space around the ship. 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.