>>95885570
MkII - there's at least one War Hound (Betrayal p93) equipped with it during the Cerberus Suppression, which was a void/zone mortalis engagement; the page notes that the XIIth were among the first to be fully equipped with MkII; there's an IF on p66 of Extermination whose armour bears significant heraldry from the Unification Wars (and was potentially issued toward the end). But the XIIth didn't participate in the Luna engagement while the VIIth did, and they're described on p81 of Betrayal as "clad in suit-sealed armour"

so to answer your question, at least as early as 703.M30, there was MkII