In a book about Farsight: Crisis of Faith (it deals with the departure of The Great Reclamation, 745.M41), Tau scientists analyze a salvaged warp drive and find organic material in it along with many praises to the Omnissiah.

I doubt that this is the navigator, since the navigator can only guide the ship and does not actually power it (drive it ? propel it ?).

It could also just be a servitor, because in the same book

Farsight wants to damage a warp drive and deals with servitors inside the warp drive.

There is no information in the wiki entry about how the drive itself works, neither in the fandom nor in the Lexicanum.

How does a Warp drive work?

  • 6
    If it's neither on Lexicanum nor Fandom, I doubt it has ever been explained in any kind of details. The most detailed description I know is "it rips a hole into reality to go into warp".
    – Shade
    Commented Sep 14, 2020 at 21:24
  • It is worth to point that Space Hulks (which are in fact a joined together pieces of shipwrecks) can go in and out of the warp as long as they do it far away from the star and they can do it without working warp drives. This would suggest that passing from realspace to warp is a relatively easy and natural process and the warp drive itself just helps to do it in a more convenient way.
    – Yasskier
    Commented Oct 26, 2020 at 19:46

3 Answers 3


Warp Drives Make the Hole, Gellar Fields Keep You From Dying, Navigators Make Travel EASY (some restrictions apply)

A warp drive tears a hole in realspace via some fancy manipulation of the barrier separating realspace from the Immaterium. It's entirely mechanical in nature, apart from a few bits of organic matter for processing power. We know this because human Warp Drives have been around since before human psykers. As a complex machine it would have to have some organic components, by Imperial and Mechanium law, but that's probably all vat-grown. The revolt of the Men of Iron means ALL sufficiently complex machinery requires "wetware" (brain/nervous system tissue from a biological source) to guard against another AI revolution. It stands to reason that, if the Tau captured a Warp Field Generator, there would be biological bits attached as whatever hard-wired servitors or brains-in-jars used for processing power would obviously be biological in nature. Interestingly, it does NOT need a navigator to operate, or indeed any kind of psyker. There's a note about in one of the Eisenhorn books, though I forget which one. Once you're in the warp, you need a Gellar field (more on that in the end) to keep your ship from being torn apart by literal hell, and if you want a real chance of moving quickly you need a Navigator. Without the Navigator you can still travel using the warp drive, but it's HARD.

How hard? You MIGHT be able to do a 3-5 lightyear jump without too much hassle. A 10 lightyear jump is dangerous-to-the-point-of-desperation, and anything more than that simply WILL get you killed and/or lost. There are occasional warp gates/tides in the warp that enable ships to do better than this, but it's VERY rare on a galactic scale. That thing the Tau do? Break into the warp the barest fraction and sorta "skip" across the barrier to go FTL for short hops? That's essentially what EVERYBODY BUT HUMANS have to do if they're doing warp travel. (Apart from Orks, who just don't care about being lost for centuries or arriving yesterday or way the hell from where they aimed.) A Tau warp engine isn't necessarily worse than a human one, but without the navigator as a guide or the Astronomicon as a beacon it's too dangerous to attempt a long-range warp jump.

The real technology (if you can call it that) advantage the Imperium has is the Navigators, which allow their ships to use their warp drives without too much fear of being lost in the warp or arriving wildly off course. In Rouge Trader (and supported throughout the more recent fluff up to the 7th ed rulebook, which is the latest I have) it's the navigator's ability, combined with the Astronomicon, to travel hundreds of lightyears via the warp at a go which makes the Imperium so successful. Otherwise it simply would not be able to maintain it's massive stellar empire. Navigators do this via their third eye, which allows them to look into the warp without going mad and helps them "steer" the ship. Most navigators see an ocean of swirling colors when they stare into the warp, but some see jungles made of faces, infinite ever-changing shapes, or other weirdness. But regardless they can sense warpstorms and somewhat avoid them, as well as the largest warp-predators which might overpower your Gellar field and faster tides which will take you to your destination quicker.

My guess is that the Tau, being a non-psychic race, haven't really grasped this concept. So instead of trying to reproduce the (biotech?) of the navigators they are instead looking at human warp drives to figure out how humans can have such a large reach. Because OBVIOUSLY it's the engine that's substantially better than Tau stuff, not some witchy mumbo-jumbo coming from a mutant with a 3rd eye. Obviously THAT is just backward monkey superstition!

Gellar Field A Gellar field works by wrapping a ship in the bubble of realspace. Beyond that not a whole terrible lot is known.* Based on books like Execution Hour it appears to be a completely mechanical devise, as far as that goes in the Imperium of Mankind. I say that because there is almost certainly some level of biological components to it, just like the Warp Drive.

*I doubt very much it works via "the mind of a human psyker" because Gellar fields were developed before psykers were numerous and there has never been a recorded instance of the psyker causing problems. (In all the thousands of GW books and fluff pieces, not one reference to a Geller-field-psyker dying, being replaced waking up, or otherwise being problematic.) At a bare minimum, warp anomalies seem to make it easier to enter the warp, and ships have had their gellar fields "flicker" while in the warp, but not be destroyed. If there was a living comatose psyker responsible for the field they'd be the first target for demonic possession/intervention. The simple fact that Gellar Fields can still be activated under such circumstances is a pretty solid sign there are no psykers directly involved.


For an imperial ship to travel through the warp, several components are required:

  • Warp Drive
  • Navigation
  • Propulsion

Warp Drive

The Warp Drive consists basically of two main pieces:

  • Warp Drive
  • Gellar Field

Warp Drive

The Warp Drive is not a "Drive" in the tradional sense like the Plasma Drive. It is more of a tunnel maker, i.e. it rips a hole into reality and enables the ship to transit from Real Space into Warp. The reason for warp travel to be that much faster than real space travel is that distances are not the same. However, there are no "fixed" points in warp, i.e. it is not possible to simply see where you came from and where you go. You therefore need means to navigate in the immaterium, which in the Imperium is mostly done using Navigators.

Geller Field

The Geller Field is a shield that casts a bubble of real space around the ship, i.e. making sure that the warp does not get into the ship. This would have dire consequences, daemons using the crew as playings is probably one of the worst.

The reason I say the Gellar Field is part of the Warp Drive:

  • It is not possible to dive into the warp without a Gellar Field. As mentioned, this would expose the warp to the crew and the ship itself. Daemons could then easily possess the crew and the ship.
  • In the Rogue Trader RPG, Warp Drives are huge, easily the biggest single component together with the plasma reactor. The Geller Field does not use any space in the ship, only energy.
  • On the Fandom, Geller Field is described in the Warp Drive article.

Checked Fandom and found the following (emphasis by me):

All Imperial Warp-capable voidcraft possess a special module attached to the Warp-Drive which emits a unique 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.

In truth, the Gellar Field is a field of reality whose source emanates from the dreams of a psyker kept in a hibernating, comatose state. In their coma, they psychically project an aura of normality around the ship in which the physical laws of realspace still apply.

The voidship effectively shields itself within the dreaming psykers' projections of reality which serves as the "bubble" of realspace that pushes back the Immaterium for a time. However, these psykers generally lose their lives through this process after a relatively short time, which means that any Warp-capable voidship must have new psyker "batteries" to replace the old at a consistent pace.

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.

From the Warp Drive article on Fandom

So, the organic matter might be from the psykers used for the Gellar Field (which is part of the Warp-Drive).

There is however one problem. From the same article:

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.

So, starting in the 18th Millenium, there was the Warp-Drive technology available. So, with the ability to go into the Warp, a Gellar-Field is required. The DAoT took place from the 15th to the 25th millenium:

The Age of Technology, informally often referred to as the Dark Age of Technology, was the zenith of Mankind's scientific knowledge and technological power in the Milky Way Galaxy, which lasted from the 15th Millennium A.D. until the onset of the Age of Strife in the 25th Millennium.

From the DAoT article on Fandom

The big problem with this being: there were no human psykers in the 18th millenium as the DAoT ended (among others) with the rise of the psykers:

Towards the end of the Age of Technology psykers first appeared among humanity. While persecuted on many backwards, regressive human worlds as witches, in enlightened and progressive societies these psykers were at first protected and accepted.

From the Age of Strife article on Fandom

So, to create a working Gellar-Field, a psyker is required (from the 18th millenium on). The first psykers only appear around the 25th millenium. So, whoever described how a Gellar Field works apparently has no clue about the history of mankind in the 40k universe.

One might argue that the technology from the DAoT Gellar Field was lost and the psyker is the solution from the 30th millenium on. However, there is still one big problem: the number of psykers. Psykers only appear like one in a hundred million / a billion, somewhere around there.

There is a fleet of thousands of Black Ships to get the required psykers for the astronomican (around 1'000 a day). With the fleet size of the imperium, and I mean not only the Navy but also every freigther etc. needing a load of psykers for their Gellar Field, it would IMHO simply be impossible to gather enough psykers to fuel that!

I personally, and all people I've talked about this subject, consider it a not well thought through description by somebody who didn't do basic research about the history of mankind and hasn't run through the numbers!


As aforementioned, the warp has its own rules, a normal human cannot navigate through the warp like on a planet or in space. There are basically three means to navigate in the warp:

  • Navigators
  • Calculated jumps


Navigators are human mutants of a stable strain that are able to look into the warp without become mad.

Longer jumps of up to 5,000 light years can be done by steering a ship through the currents of the warp. Only human mutants known as Navigators can do this, as they have the ability to look upon the warp without going mad from exposure to it. Within the warp they can sense the Astronomican, a powerful psychic homing beacon centered on Terra, and use it as a sort of navigational reference aid by judging its distance, strength and position so they can inform the ship's captain to adjust heading when the ship is forced off-course by warp currents. However, piloted jumps still remain unpredictable and dangerous as the Astronomican's power, though immense, is limited to a diameter of about 50,000 light years from Terra, also Warp Storms and psychic phenomena such as the Shadow in the Warp can disrupt and block the beacon.

From the Lexicanum article on Warp Jump

Calculated Jumps

This is basically a predicted jump. One calculates in advance how the warp should behave and adapts to this. This is rather dangerous and not really suitable for long warp jumps.

A short jump can be carried out by calculating the ship's projected course, corrective maneuvers, approximate journey time, and exit point before it starts the warp jump. While the ship is still in real space, its warp drive has the ability to monitor that part of the warp corresponding to the ship's current position and observe how the warp is currently flowing. But this monitoring can only be done from real space, which means this type of jump is inherently unpredictable as it relies on the warp currents not changing once the ship is in flight, as once inside the warp there is no longer any way the movements can be detected and all the ship can do is carry on blindly until it emerges in real space and hope it arrived in the planned location. Generally a safe distance for this type of jump is up to four or five light years.

From the same Lexicanum article as the quote in Navigators

There is also a archeotech device that basically does the same as a navigator, therefore greatly enhancing the reach of calculated jumps. I cannot find the description of it anymore, should be in one of the Rogue Trader RPG rule books, IIRC. Maybe I'll find it again.


Propulsion in the warp is done as in real space, i.e. with the normal Plasma Drives of the ship. Within the warp, the ship behaves like in real space, moving forward and navigating through the tide. It is the task of the navigator to instruct the bridge crew what actions to take as all windows are closed and sensors are not reliable within the warp.


With what you quoted, it can easily be imagined that the T'au did not know the difference between the Warp Drive itself and the Geller Field. This, as they don't yet have the technology to dive into the warp as the imperium has, as well as that the Geller Field is small compared to the Warp Drive and, to the extend of my knowledge, very close to the Warp Drive.

  • So basically we have no idea how it really works beside the fact that it helps.
    – Clockwork
    Commented Oct 26, 2020 at 9:20
  • @Clockwork That what helps?
    – Shade
    Commented Oct 26, 2020 at 9:21
  • Uh, I already forgot its name, let me read again. Warp-drive.
    – Clockwork
    Commented Oct 26, 2020 at 9:22
  • 1
    @Clockwork No, and GW will probably never describe how that works to precisely as it would limit their options.
    – Shade
    Commented Oct 26, 2020 at 9:38
  • The idea that the Gellar Field is powered by a sleeping psyker only dates back to 2018, when it was introduced in Ashes of Prospero. Before that, it was never explained. Also the Gellar Field isn't the Warp Drive, so this answer isn't really that relevant to OP's question.
    – Kelderic
    Commented Oct 27, 2020 at 13:30

How does a Warp drive in Warhammer40k work?

It opens a temporary hole in reality

There are no real details how it works, except that it requires a big, bulky machinery, so only big ships can use it. We know very little about it:

  • We know, that was discovered during (or actually just before) the Dark Age of Technology and that even non-psychic Tau has managed eventually to make a working copy (which has ended badly for them). This suggest, that the "core" of this technology is purely mechanical and doesn't require psychic skills or at least a "professional" psyker, but a sort of mental connection between this and other side (even "primitive" Kroot have their FTL "Warspheres") , which is why Tau was struggling to replicate this technology for years.

  • Tau managed eventually to go into warp using anti-matter (fateful AL-83 Slipstream modules). Too bad that they haven't tried to replicate the Gellar Field...

  • We know, that that Space Hulks can enter into warp by themselves - as long as they are far enough from the local star - and that Navy vessels spend often many days traveling using normal propulsion before making a jump from a "stable" warp points

  • WE know that Orks managed to weaponize the Warp generation in their Shokk-attack guns

Servitors in the drive itself wouldn't be a big surprise - after all, someone has to maintain the drive in a working condition.

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