Without your ministrations, no bolt may be fired, and no enemy slain." — Extract from the Apocrypha of Eons, Verse III, Chapter CIV

SOUCE: http://warhammer40k.wikia.com/wiki/Techmarine

"Yours is to heed the machine as others heed their kin. Tend to the war spirits all about, but do so in the knowledge that you do the Emperor’s duty. Without your ministrations, no bolt may be fired, and no enemy slain."

— Extract from the Apocrypha of Eons, Verse III, Chapter CIV

An Ultramarines Techmarine wearing the standard red colour designating his ties to the Adeptus Mechanicus

A Techmarine (known as a Frater Astrotechnicus in High Gothic) is a Space Marine technician and engineer as well as a full Astartes Battle-Brother of his Chapter. They are fully initiated members of both the Cult Mechanicus and their Chapter. Prospective Techmarines are chosen from the ranks of the Space Marine Chapters for their affinity with technology. They are sent to Mars for 30 standard years of training, and taught the machine lore. They learn how to divine the runes of engineering and study the liturgy of maintenance. This great body of lore must be committed to memory and understood by the novice Techmarine. They are taught how to "feel" the pain of a damaged machine and heal it. When they come back they serve the same role in their Chapter as a Techpriest Enginseer in the Imperial Guard.