Helios is a Forge World of the Adeptus Mechanicus, and is notable for being the originator of the Land Raider Helios, which was developed during the legendary Siege of Helios campaign in 857.M38, when the Forge World was besieged by invading Orks of WAAAGH! Grimgut. First utilised by the puritanical Red Scorpions Space Marine Chapter, they were able to use the Helios Pattern Land Raiders and successfully repel the Greenskin invaders. The grateful Archmagi who helped developed this new pattern of Land Raider ceded the design specifications over to the Red Scorpions, who later disseminated the newly developed Helios Land Raider to other Chapters of the Adeptus Astartes that they were on good terms with.
The early history of Helios is not well-recorded in current Imperial records. More than likely, it was discovered and colonised during the Dark Age of Technology or millennia later during the Great Crusade. Helios came to prominence as the originator of the Helios variant Land Raider which was developed as a stop-gap measure to provide additional artillery support. This was done by replacing the standard hull-mounted Heavy Bolters with a Whirlwind Multiple Missile Launcher and additional targeting and tracking equipment. The need for such a variant armoured vehicle came about during the legendary Siege of Helios in 857.M38, while fighting against the Orks of WAAAGH! Grimgut.
The Helios Pattern Land Raider was first developed by the famous Red Scorpions Space Marine Chapter. This Chapter is renowned for their puritanical beliefs, a deep-rooted mistrust of many other Imperial fighting forces and a highly independent streak. When the leading assault of the Greenskins had overwhelmed the manufactoria of the world of Helios, the task of repelling the Ork invaders was beyond the capability of the Astra Militarum regiments. Displaying their typically low cunning, the Orks had set loose an infestation of Bomb Squigs which boiled forth from the sewers and destroyed any vehicles attempting to press through the city's streets.
With a distinct lack of artillery able to breach the walls and suppress the Ork defenders in their sector prior to an assault, the answer to their need for swift armour artillery support came when the Archmagos of Hive Manufactory 33 Delta Thule, an ordnance foundry which had long supplied missile launchers to the Red Scorpions, received what he later claimed was a vision granted to him by the Machine God. By fitting the foundry's weapons systems to the Red Scorpions' Land Raiders, the attack force was able to mount its own artillery support on vehicles all but immune to even the most concentrated effort to overwhelm them and the hive city, and all of Helios, would be delivered. Within twenty-four solar hours, every one of the dozen Red Scorpions Land Raiders deployed to Helios had been converted to what would later become known as the Helios Pattern Land Raider.
In the resulting battle, the dozen Land Raiders Helios led the Red Scorpions strike force deep into the Ork-held hive. As predicted, a tide of Bomb Squigs erupted from the sewers to break against the vehicles. Once the resulting explosions cleared, the Land Raiders were charred black and splattered with steaming Squig blood but otherwise intact, while the entire wave of Orkoid creatures had obliterated itself to no effect whatsoever. The route into the hive was finally open and the doom of the Orks of WAAAGH! Grimgut was at hand.
The lifting of the Siege of Helios saw the pattern named after it became a standard part of the Red Scorpions' Chapter armoury. In recognition of the deliverance of the hive, the master of Manufactory 33 Delta Thule ceded the pattern's sanctified specifications to the Red Scorpions, who disseminated it to the small number of Chapters they had close relations with. In later years, a further refinement of the pattern would be developed at Helios. Rather than mounting a standard Whirlwind Missile Launcher, the Hyperios variant mounts a version dedicated to anti-aircraft operations.
- Imperial Armour Volume Two - Space Marines & Forces of the Inquisition, pg. 105
- Imperial Armour Volume Two - Second Edition: War Machines of the Adeptus Astartes, pg. 18, 34-35