The Ironwing was one of the six wings of the Dark Angels Hexagrammaton, they were dedicated to the use of overwhelming firepower on the battlefield.
Not a subtle wing, utilizing massed armor, artillery, and dreadnoughts. They excelled in siege breaking and the rapid onslaught of massed armour. Its Marshals were experts in the art of destruction of enemy war machines and heavy guns, often called upon to oversee the destruction of apocalyptic engines encountered by the First Legion in its early days.
Created from the Hosts of Stone and Iron, the Ironwing also included a large amount of infantry in the form of heavy weapons units, Breachers, and Terminators. During the last years of the Great Crusade the Ironwing fielded the largest concentration of Terminators of all the Legions, including experimental patterns of armour unknown to the wider Space Marine Legions. These were most commonly used to storm enemy fortresses and gained fearsome reputations; many of those warriors would resume wearing the iconography of the Host of Stone and refer to themselves as "Stoneborn".
The Lion claimed that the Ironwing was functionally just as good at sieging and fortifying as the Iron Warriors and Imperial Fists, but stylistically unique. For example, when the Lion tasks Duriel with building a fortress, the reason the fortress is so strong is because of its design. Ironwing fortresses are intended to be a maze that cannot even be navigated by the majority of the Legion's command hierarchy. Each commander knows the layout of his assigned position and nothing more, preventing enemies from navigating the fortress and allies from giving up weaknesses. Only the Lion and the Voted-Lieutenant of the Ironwing knew the complete design of the fortress.
The Ironwing also contained a high concentration of the First Legions Techmarines, who were responsible for maintaining their unique weapons and tech. These marines enabled the Dark Angels to function independently, with the bare minimum number of Mechanicus cronies; of all the Wings save the Dreadwing the Ironwing was most hated by the Mechanicum due to their hoarding of forbidden technology.
The Ironwing took grievous losses in the early years of the Horus Heresy and by the end of the rebellion was a shadow of its former self. Perhaps because of their losses, the Ironwing has not survived in any meaningful sense into the 41st Millenium, although it seems their excess of Terminator suits and their technical expertise were distributed throughout all of the Dark Angels successor chapters and explains how they are able to maintain and manufacture more, even when new successors get raised.
- Duriel - Voted-Lieutenant of the Ironwing during the Great Crusade and the Rangdan Xenocides and a major character in the Lion's primarch novella. Known as a skilled master of siege warfare and was tasked by the Lion with constructing a stronghold that could resist the Khrave attackers. Ultimately died during the conflict when he personally nuked a titan that had been possessed by the Khrave.
- Venerable Titus - Voted-Lieutentant of the Ironwing. He was a dreadnought and hence could not "take the chair". He had passed through at least one chassis before finding himself in command of the Ironwing. Fun fact, Titus was old enough to have fought with the emperor during the Unification Wars.
Despite the Ironwing being described as having the highest concentration of Terminators out of any Legion, and also being described as having Terminator Patterns that are unknown anywhere else, GW/FW missed a trick by not describing them or releasing any of them. Furthermore, the benefits of Scions of the Ironwing rule are generally lost on a squad of Terminators, since it only really helps when shaking vehicles, (the jury is out on whether it even works the way it is supposed to vs Extra Armour) and is pretty redundant on any squad of Terminators with Power Fists/Chainfists/Hammers.
The Ironwing are represented on the table top by an Excindio Class Battle-Automata, an enslaved Man of Iro... I mean: a completely ordinary Terran built combat robot.
While it does sound like it has the cool factor, there are issues with its cost and viability on the tabletop, not least the fact that if it gets wounded there is a 17% chance it will go on a rampage and start killing the nearest unit, including its allies. There is even an "upgrade" for Techmarines that allows them to try and kill the Excindio if this ever happens, which tells you about as much as you need to know about how the Ironwing were balanced...
Probably going to be a mod of the Castellax molds because Games Workshop are slackers.