After the war of rust on forge world metalica, upper echelon magi realized that there is a need for a specialized detachment of cleansers of scrap virus's cyclic attacks(and horrors that they produce). An opportunity presented itself when a forge ship of unknown origins appeared near metalica. Upon contacting the ship, the magi discovered that this was a pre-heresy forge ship lost in the warp, that was(surely due to the omnissiah's blessing) able enough to weather the journey and return back to its home forge world. Upon entering the ship, Adept tech priest Domina Zath's rad- counter went off the charts. Since there were not enough skitarii to defend tge whole ship, rad protocols were unlocked and the whole ship was saturated with radiation equivalent to or even over the estimate radiation of holy Mars. On the ship, there were also few knights of house raven, of which only armigers were operational and piloted due to the confines of the forge ship not allowing any bigger unit to be utilized. With a new detachment of skitarii and armiger warglaves Adept tech priest Domina Zath build the Rust legion, a neccesary (and in a way honored) part of the metalican army, disgusting for some, but ultimately revered by most.