How do Necrons travel through space?

Question

The Eldar have the Webway. Humans go through the Immaterium. How do Necrons travel?

Answer 1

From Warhammer TV Twitch, Index Necron, from Minute 36:51 on:

They don't use the warp for any kind of technology, actually thats an interesting... that's a real difference sort of as humanity moves along and discovers warp travel, that kind of thing. Lot of other races use warp travel.

Not so the Necrons. They can harness sections of the webway with what is called dolmen gates that allow them to sort of travel sections of the webway and travel through them themselves.

...

They have inertialess drives in their tombships that allow to hackle around the galaxy with incredible speeds.

From this twitch video of WarhammerTV, from around 2019 (no date on the video)

So, they are using both. The difference seems to be the size of the ships. In the video, intertialess drive is mentioned for tombships, which is basically their biggest class of ships, with about 15km width. For tombships, the webway (i.e. dolmen gates) are not suitable.

Concerning Dolmen Gates, it's not like they are readily available:

In the aeons that have passed since the War in Heaven, the Dolmen Gates became lost or abandoned during the Great Sleep or destroyed by the Eldar whilst the Webway itself has become a tangled, broken labyrinth.

From the Lexicanum article on Dolmen Gates

It would therefore seem that the Necrons way of FTL travel is Intertialess Drive for their biggest ships and for smaller ships using the remaining Dolmen Gates.

As for retcon, to be complete.

In Codex Necrons, 3rd edition, no specific name is given to their drive.

Armed with weapons of god-like power and ships that could cross the galaxy in the blink of an eye, the Necrontyr stood ready to begin their war anew.

Codex Necrons, 3rd edition (2002), page 25

From the 5th edition, we have the Dolmen Gates but I could find no mention of the intertialess drive:

Necron legions finally broached the webway and assailed the Old Ones in every corner of the galaxy.

Codex Necrons, 5th edition (2011), page 7

Also:

Imotekh takes control of the Sautekh Dynasty. Executing any noble foolish enough to stand in his path, Imotekh cements his position by naming himself phaeron. Within a year of his awakening, the dolmen gates and Tomb Ships of Mandragora are restored, and Imotekh’s reconquest of the galaxy begins in earnest.

From Codex Necrons, 2015 (page 83 of the web optimized codex I got)

So, since the 3rd edition, no mention of the inertialess drive any codex but it was mentioned in an official WarhammerTV broadcast in around 2019. We can therefore assume that Necrons have Inertialess Drive and Dolmen Gates for FTL travel.

Answer 2

The Battlefleet Gothic Armada rulebook states

Inertialess Drives are propulsion systems used by the Necron Fleet that are capable of interstellar travel without the need to enter into the Warp.

The 5th edition Necron Codex mentions the use of Dolmen Gates, which allow travel through sections of the webway that have been sealed off from the Elder areas of the webway.