The Warp-Drive, or Warp Engines, are devices integrated into spacecraft used by many intelligent races to actually enter the Warp, an alternate dimension of purely psychic energy that echoes and underlies the familiar four dimensions of realspace, making them capable of a form of faster-than-light travel known as Warp travel or Warp jumping. The Warp-Drive allows a starship to enter the Warp, travelling its currents until reemerging into realspace tens, hundreds or even thousands of light years away from the starting point. They are huge and bulky devices which only large voidships possess the cargo capacity to carry. Starships fitted with Warp-Drives are known as Warpships or Warp-capable voidcraft. Warp-Drives allow starships to enter the Warp and bypass light years of realspace in a relatively short time, although the myriad dangers associated with Warp travel are terrible indeed.
The Warp-Drive was invented by Mankind sometime in the 18th Millennium of the Imperial Calendar during the early Dark Age of Technology. Prior to this time, interstellar travel for the voidships of Mankind was limited to sub-light speeds. Travel between star systems was painfully slow, taking many generations of travel, and most human interstellar colonies were isolated outposts established by the crews of generation starships or vessels that made use of suspended animation technology. The Warp-Drive was one of the most revolutionary inventions in human history -- what had once taken many generations of human lives now took only days or weeks. Consequently Mankind's colonisation of the Milky Way Galaxy was vastly accelerated beyond what it would have taken had humanity been forced to remain wedded to conventional reactive propulsion technologies. Consequently Mankind's colonisation of the Milky Way Galaxy was vastly accelerated in scope and timeframe beyond what would have been possible had humanity been limited to conventional reactive propulsion technologies. In approximately the 22nd Millennium, further technological progress led to the creation or the discovery of the human mutant Warp-pilots known as Navigators. These mutants allowed Warp-capable spacecraft to make longer, safer and more accurate jumps through the Warp, and further accelerated the galaxy's colonisation by humanity until the Warp Storms of the Age of Strife in the 25th Millennium prevented further Warp travel and once more isolated all the human-settled worlds from one another for almost 5,000 Terran years. Only the coming of the Emperor of Mankind and the launch of his Great Crusade at the dawn of the Age of the Imperium in the late 30th Millennium would reunite the scattered worlds of humanity under the aegis of the Imperium of Man.
Once a spacecraft activates its Warp-Drive, it is plunged into a dimension very different from the material universe. It is convenient to imagine Warpspace as consisting of a relatively dense, almost liquid, energy, devoid of stars, light and life as it is commonly known. Once within Warpspace a Warp-capable voidship may move by means of its main reaction drives, following powerful eddies and currents in the Warp, eventually reaching a point in the Empyrean corresponding to a destination in realspace. The most difficult aspect of Warp travel is that it is impossible to detect the spatial movement of Warpspace once a ship is in the Warp. The ship can only blindly carry on, its crew trusting that it is going in the right direction. The longer a ship remains in Warpspace, the greater the chances of encountering some unexpected current that can turn it unknowingly off-course.
Navigation of Warpspace can be achieved in two ways: the calculated jump and the piloted jump. All Warp-Drives incorporate navigational mechanisms. When the ship is in realspace, these algorithms monitor the ever-shifting movements of that part of the Warp corresponding to the voidship’s current position. It is essentially a "window" into Warpspace. By means of observing these movements in the Warp it is possible to calculate a course, corrective manoeuvres, and approximate journey time to a proposed destination in realspace. Calculation relies on the assumption that the Warp-currents observed from realspace do not change significantly during flight. This method is known as a "calculated jump", but is often referred to as a "blind jump" by Imperial Navy personnel. It is not safe to make a calculated jump of more than four light years at one go. The longer the jump, the greater the chances of a significant change in Warp current movement.
The second, and more efficient, form of Warp-navigation is the piloted jump. This method relies upon two factors: a pilot who can gaze into the Warp and guide the ship around the hazards to be found there, and a stable reference point to triangulate one's position against. The Imperium uses the mutants known as Navigators as Warp pilots and the psychic beacon of the Astronomican as a reference point. The Astronomican is centred on Terra and is not only controlled by, but is directed by, the potent psychic power of the Emperor of Mankind. The Astronomican is a psychic beacon that penetrates into Warpspace all the way out to a diameter of approximately 90,000 light years from its source point in the Imperial Palace on Terra. A Navigator onboard a voidship in the Warp is able to pick up these psychic signals and can steer a spacecraft through Warpspace, compensating for current changes as he does so. A piloted jump can cover a far longer distance than a calculated jump. Most piloted Warp jumps are no more than 5,000 light years at a time, but longer jumps have been made. Renegade and Chaos voidships often lack Navigators (as most Navigators opt for suicide rather than betray the Imperium), but they compensate by using a Possessed Chaos Space Marine or another Daemonhost as a pilot, as such blasphemous mingling of man and daemon are just as capable as any mortal Navigator of safely guiding a voidship through the currents of the Empyrean.
After several weeks of travel, the Warpship arrives at its first destination. This is the "jump-point" lying around the star system like the circumference of a circle. This delineates the point at which interplanetary debris falls below maximum Warp density. Once this invisible line has been crossed, it is safe to activate the vessel's Warp engines. A crew careless or foolhardy enough to prematurely activate its Warp-Drive would be lucky to only find their ship hurled thousands of light years off-course. More likely, the starship would be torn apart and destroyed, never to be heard of again. With the safe activation of its Warp-Drive, the ship is plucked out of the real universe and enters the ethereal dimension of Warpspace. Its true interstellar journey has begun.
All Imperial Warp-capable voidcraft possess a special module attached to the Warp-Drive which emits a special protective force field called a Gellar Field. The Gellar Field creates a "bubble" of realspace around the starship that it essentially carries into the Empyrean alongside it. The Gellar Field protects the starship 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 the field or even survive outside the Immaterium except under very precise conditions or special circumstances. The weakening, failure, or collapse of a Gellar Field while the starship is travelling through the Warp would be completely disastrous. Warp entities would tear the ship apart to reach and consume the souls of its crew and passengers.
An unprotected human in the Warp may be possessed by alien or daemonic entities or driven insane by the phantasmal environment itself. People disappear without trace, while crazed mobs rampage through the decks living out their nightmares, leading to widespread murder and self-destruction. Sometimes a vessel emerges from the Warp physically intact but with no trace of its crew. Many such ghostships drift through the galaxy, and they are considered an ill-omen by all those who encounter them while sailing upon the ebon sea of the void.
- Codex: Chaos Daemons (4th Edition), pg. 43
- Rogue Trader: Core Rulebook (RPG), pp. 181, 183, 192, 199, 227, 310-313, 316-317
- Warhammer 40,000: Rogue Trader (1st Edition), pg. 131
- Warhammer 40,000 Rulebook (6th Edition), pg. 146
- Warhammer 40,000 Rulebook (4th Edition), pg. 122
- Execution Hour (novel) by Gordon Rennie
- The Horus Heresy - Book Two: Massacre (Imperial Armour), pg. 27