The World Engine was the name given by the Imperium of Man to a monstrous mobile artificial Tomb World of the Necrons of the Neokhares Dynasty, known to those undying xenos as Borsis. It was discovered in the Vidar Sector of the Imperium in 926.M41 after the Necrons hibernating in stasis tombs beneath its metallic surface rose from the Great Sleep. This Necron planet-sized weapon was armed with an array of deadly Gauss Projectors capable of scorching away all life on the surface of an entire planet. Presenting a hideous threat to the security of the Imperium once its existence was discovered, the World Engine was attacked in the Vidar Sector by 15 Space Marine task forces supported by elements of the Imperial Navy. Despite their best efforts, the Imperial task force was unable to penetrate the World Engines' superior defences, attempting at least a dozen times to overwhelm the massive construct with sheer firepower. The Imperial forces were rewarded for their efforts with many destroyed and crippled starships and millions of casualties. Finally, in desperation, the Astral Knights Space Marine Chapter rammed their flagship into the World Engine in a suicidal charge, and then deployed its surviving Battle-Brothers onto the Necron vessel's surface. After fighting for over 100 solar hours, the surviving Astral Knights reached a Necron command node and planted Melta-charges that destroyed the vast Necron tomb complex that housed many of the World Engine's command arrays. This brought down the vessel's impenetrable Void Shields and also silenced the World Engine's advanced weaponry. The sacrifice of the Astral Knights allowed the Imperial Navy's starships to finally destroy the World Engine with Cyclonic Torpedoes.
The massive mobile artificial Necron Tomb World of Borsis, designated the "World Engine," by Imperial military command, was attacked after it went active in the Vidar Sector in 926.M41 by task forces raised from 15 separate Chapters of the Adeptus Astartes plus multiple elements from the Imperial Navy, and even the mightiest weapons the Imperial forces could bring to bear could not harm it. Drop Pods and torpedoes could not penetrate its potent defensive shields and it was impossible to lock on to the massive vessel's interior with teleport beams. The Imperial task force tried twelve times to overwhelm it through sheer valour and firepower and was rewarded with a string of destroyed and crippled starships and millions of casualties. The World Engine destroyed a third of an entire Imperial Navy battlefleet before the Chapter Master of the Astral Knights decided to ram the hideous vessel with his Battle Barge, the Tempestus. It was only when the enormous Space Marine starship collided with the Necron construct's shields that they finally failed, allowing the Imperial forces to approach their target. A force of over 700 Astral Knights deployed from Drop Pods onto the Necron vessel's surface. For over 100 solar hours the Astral Knights fought against tens of thousands of Necron warriors and destroyed every flux generator, weapon forge and command node they came upon. Only after the Chapter had been reduced in size to the Chapter Master, Arthor Amhrad, and five Battle-Brothers did they succeed in their quest. Amhrad detonated Melta-charges that destroyed a vast Necron tomb complex at the centre of Borsis that housed many of the World Engine's command arrays. This detonation brought down the vessel's seemingly impenetrable Void Shields and also silenced the mobile Tomb World's potent weaponry. This allowed the Imperial Navy's starships to destroy the World Engine with Cyclonic Torpedoes.
After the battle, as the Adeptus Mechanicus picked over the shattered remains of the destroyed World Engine in an attempt to salvage any valuable technology and rescue any survivors, the Ultramarines retrieved the twisted wreckage of the Tempestus and placed it amid the ruins of Safehold, the last planet scoured clean of all life by the World Engine. The 2nd and 4th Companies of the Blood Angels had been amongst the Astartes task forces dispatched to the Vidar Sector to assist their fellow Space Marines against the threat posed by the World Engine. After the sacrifice of the Astral Knights lead to the final destruction of the World Engine, Captain Donatos Aphael of the 2nd Company proposed that an Imperial shrine be erected upon the world of Safehold in eternal memory of the Astral Knights Chapter. The shrine today consists of seven hundred and seventy-two arbalstone statues, one for every Astral Knight Battle-Brother that died stopping the World Engine. These statues stand a silent vigil within the dead heart of the ruined Tempestus. From that day forth, 2 Blood Angels of the 2nd Company, and Battle-Brothers from nearly a dozen other Chapters, are always assigned to stand guard over the memorial, which is considered a singular honour for the Astartes that fought beside them for the last time.
- Codex: Blood Angels (5th Edition), pg. 16
- Codex: Grey Knights (5th Edition), pg. 38
- Codex: Necrons (5th Edition), pg. 26
- Codex: Space Marines (5th Edition), pp. 44-45, 49, 74
- The World Engine (Novel) by Ben Counter
- Crossed Swords (Novella) by Ben Counter