Board Thread:Questions and Answers/@comment-30488984-20180209014659/@comment-32334892-20180209130334

"The Taghmata Omnissiah (translated from Lingua-technis into the Terran Gothic of the Imperial Court as, "That which is divinely ordered for war") was the principal type of operational military force of the trans-Martian Mechanicum and also the most numerous at the time of the outbreak of the Horus Heresy during the opening years of the 31st Millennium"

seems to me that it was the Mechanicum's Pre-Heresy primary military force. so unless your going to Pre-Heresy you don't have write about them.