From Strength Cometh Will

IWs squad of Havocs (heavy weapon specialists) with Lascannons and a Predator MBT.
As it was said, Iron Warriors are stereotyped as a "Ranged Warfare Legion", because their specialization involves a lot of heavy weapons. In fact, Iron Warriors were the first legion to call heavy weapon squads "Havocs", back during Great Crusade (Though Iron Havocs were veteran HWS, not just any).
In addition, said specialization, as well as tight contact with (Dark) Mechanicum, resulted in Fourth Legion having one of the widest vehicle park.