When the Imperium of Man's vanguard, led by Abaddon the Despoiler, forcibly landed on Canopy Star and began a never-ending battle with the Orks; when their fleet in space launched a sneak attack on Horus's main fleet and became entangled with the enemy's infiltrating fleet, intercepting and counter-intercepting one another; and when a certain troublesome little girl of a supreme commander finally remembered something important and hurried back, the secret mission that the leaders of the mining base had placed great hopes in was already quietly underway.
After waiting for two days, the order finally came. Wang Qing's entire squad, together with a female Astartes named Mulan and Colonel Daqi's squad, made up a total of thirteen elite assault troopers. They used the base's dedicated short-range one-way teleportation gate to enter the protective shield of the Necrontyr tomb complex, then launched a full-scale assault on the first level of the underground obsidian tomb.
That was right!
With their supreme commander's guidance, the base's researchers had long since cracked the shield surrounding the Necrontyr tomb complex—a shield that was nearly impregnable and had spatial properties. After making preparations, they could just barely open a small one-way teleportation gate leading inside.
Originally, senior officers such as Darius had considered opening a gate and shoving in a pile of fusion explosives or high-yield fusion missiles, then taking out all those metal skeletons at once, like trapping turtles in a jar.
But the obsidian tomb material might prove useful, and it was the only material they had found so far that could amplify a Geller Field and target Warp Daemons. Destroying it along with the Necrons would be a poor trade. On top of that, the powerful C'tan might escape as a result, causing needless chaos. So they had refrained from taking any action.