Every Chapter of the Adeptus Astartes depends upon a caste of warriors who understand the sacred mysteries of its machines, and these are the Techmarines. Chosen as aspirants and sent to distant Mars, they endure long years of instruction among the tech-priests of the Adeptus Mechanicus, returning bound by oath to both their Chapter and the Cult of the Machine God.
A Techmarine's charge is the Chapter's arsenal of holy technology: its tanks and gunships, its bolters and power armour, and the revered Dreadnoughts in which the honoured dead fight on. Machines of the Imperium are held to possess machine-spirits that must be appeased with rite and incantation, and it is the Techmarine who performs these rituals, soothing temperamental engines and restoring the war-wounded to service.
Marked by the red robes of the Martian priesthood worn over their armour and augmented with a servo-harness of mechadendrites and servo-arms, Techmarines can repair even grievous damage amid battle, and defend the Chapter's relics with bolter and plasma. Under the Master of the Forge they keep the Armoury, standing as the essential bridge between the Emperor's warriors and the ancient, dwindling technology upon which their survival depends.