Over the next few months, similar scenes played out again and again on different fortress worlds.
The calculations of the Men of Iron were cold and precise.
How long each planet would hold, when to evacuate, and the maximum casualties its final destruction could inflict were all incorporated into an immense war model.
Supported by the ruthless coordination and efficient calculations of the Men of Iron, Imperial forces, both mortal soldiers and Astartes, conducted the most efficient strategic withdrawal with the lowest casualty rate in the history of the Imperium of Man.
Relying on sturdy fortifications built in advance by the Men of Iron and an endless stream of supplies, they wore down immeasurable numbers of the Tyranid Swarm.
Once countless worlds reached the peak of their tactical value, they met the same fate as Volar IX, detonated as gigantic bombs to consume billions of swarm organisms, or simply collapsed by gravity into fleeting singularities.
The meat grinder of steel and flesh always came to a temporary halt when the side of steel deliberately blew up the grinder itself.
Hundreds of billions of Astra Militarum soldiers and hundreds of thousands of Adeptus Astartes withdrew in succession to the second defensive line within Segmentum Tempestus.
This defensive line now stood on Imperial territory.
They brought with them precious combat experience and an entirely new understanding of humanity's ancient technology.
Meanwhile, the Necron Tomb Ship fleets and the main Titan Ship forces of the Men of Iron remained tireless reapers.
In the dark void at the galaxy's edge, they continued waging seemingly endless harassment and attrition campaigns against the Tyranid Swarm's main forces.
The Necron World Engines made precise dimensional jumps, every appearance accompanied by the annihilation of vast swathes of Hive Fleets.
Gauss Beams disintegrated everything, leaving only material residue drifting