Iron Hearts - Chapter History: Almost nothing is known of the Iron Hearts' origins, history or notable actions, save for the fact that shortly after their Founding they were charged with the keeping of the Mimesis Engine.This arcane artefact had been developed over solar decades by Tech-priest Lexmechanics, Artisans and Logises using ancient virtual reality technology that was already old when the Emperor rose to power. It had been unearthed from the past and was used to assist the training of Space Marine neophytes by creating simulated worlds on which Astartes-in-training could fight, die and fight again. They would learn from their mistakes without paying the true price of a failed strategy -- their own death and the deaths of their fellow Astartes.However, doubts were raised in the Adeptus Mechanicus about the sanctity of such an enterprise, and the purity in the eyes of the Machine God of any technology that set out to re-make the universe. Eventually, even the Space Marines scorned it, stating that "a Space Marine prays for only one chance -- the chance to die serving the Emperor."In the face of this opposition, the project's supporters proposed that the Mimesis Engine be assigned to the Iron Hearts, to be used in the earliest stages of their neophytes' training. Lexmechanics would monitor the combat performance of these Astartes and evaluate the technology's usefulness.During the solar decades that followed, neophytes came and went, climbing into the rod-and wire-strung battlesuits that enabled them to interact with the virtual worlds generated by the Mimesis Engine. Each exercise was preceded by ritual invocations of the Emperor's protection from any possible taint of Chaos that might arise from contact with the device and would end with a Service of Absolution in the Iron Hearts' Chapel of Martyrs.Over time, interest in its use dwindled and fewer neophytes were sent to do battle with the simulacra of Daemons, Genestealers, Orks and Aeldari generated by the artefact. The Mechanicus team of Tech-priests maintaining the device was gradually reduced until only a single technician, named Tydaeus, and a servitor designated Barek remained.The project was finally doomed when a horde of Khornate Daemons led by the Chaos Lord Kargon the Seed-Bearer unwittingly moved from the Warp to Ilium, one of the many fictitious, simulated worlds generated by the mysterious systems of the Mimesis Engine. Then Instructor-Sergeant Tydaeus, keen to prove his worth in spite of his body's rejection of the Chapter's gene-seed, ensured the program was isolated from reality and introduced himself into the simulation as a powerful Terminator to single-handedly annihilate the emaciated invaders.However, Kargon managed to regain his strength by killing several of his daemonic minions and absorbing their power. He then bested the simulated Tydaeus Terminator in combat. The Chaos Lord proceeded to use Tydaeus' mental link with the real world outside the simulation to move from the virtual universe directly into realspace to invade the Iron Hearts' outpost with his Bloodletters.The fate of the Iron Hearts after this surprise attack is unknown, but at least one company, led by Captain Christus, was away on a search-and-destroy mission at the time of the Chaos assault.