Editors' Note - This is a review of a Horus Heresy unit and thus it is written mostly in the context of gaming in the Age of Darkness rather than Warhammer 40,000.
The Iron Circle
An Elites choice that is neither Unique or dependent on taking the Primarch that commissioned them, the Iron Circle are undeniably the most striking unit exclusive to any Legion - ask yourself if any other Legion has access to their own squads of monstrous creatures to form the bodyguards for Primarchs and lesser characters. It's almost unfair to think that the Iron Warriors get all the "goodies" with regards to their legion-specific unit selections in terms of either raw destructive capabilities or visual splendor, but rest assured that the Iron Circle aren't quite as terrifying or over-powering as their background would suggest. Yes, a unit of between one and six Domitar-Ferrum class Battle Automata is always going to be scary no matter what they are equipped with and, yes, there are only a handful of more imposing sights to face on a battlefield set during the Horus Heresy. However, a smattering of core weaknesses coupled with their incredibly high cost does relegate these to thematic armies more-so than competitive ones, but that doesn't mean they aren't without some incredible abilities.
First up, the Iron Circle is a unit of monstrous creatures that can be joined by any single Iron Warriors Independent Character or Perturabo himself; they are the largest and most imposing bodyguards imaginable. This leads to all sorts of crazy effects when mixed units are in play per the recent Warhammer 40,000 core rulebook FAQs, but principally you need to look at the Iron Circle for what they are - an escort for your Warlord that can "ferry" them across the battlefield safely and allow them to either survive or strike at the foe. They are Fearless and thus immune to any kind of Morale shenanigans while they possess Adamantium Will for some added defence against Witchfire and Malediction type psychic powers. Short of a Warlord Titan, there's almost nothing that can hold a candle to the Iron Circle for raw durability in a maxed out unit of six-strong; with four Toughness 7 wounds per model, a 3+ armor save and 5+ invulnerable save, there's little that the Iron Circle can't withstand. Of course, that's before you account for all of their crazy defensive special rules; if two or more models from the Iron Circle are in base contact with each other then they gain a 4+ invulnerable save and get to re-roll failed armor and invulnerable saves against all Blast and Template weapons.
That particular ability is utterly insane as it means that a pair of Domitar-Ferrum models can, assuming average rolls and rounding up where necessary, withstand ten Wraithguard firing their D-Scythes and landing maximum hits per template with one of the Iron Circle surviving the attack - how many units in the game can lay claim to that? However, for the Horus Heresy in particular, it makes the unit all but invulnerable to the increasingly common Typhon and Medusa Siege Batteries and allows them to withstand almost all punishment. Additionally, enemies that charge the Iron Circle when the Domitar-Ferrum Automata aren't locked in combat already will be forced to make a disordered charge and thus lose the bonus attacks for charging, cutting out much of the punch needed to take the vigilant monsters down. Even more incredulous is the fact that any Independent Character joined to the Iron Circle benefits from all of their defensive abilities, including the free 5+ or 4+ invulnerable save and re-rolling failed armor and invulnerable saves against blast and template weapons - who needs to pay for an Iron Halo when your bodyguard holds it above your head free of charge? With the change to grenades in close combat allowing only one such model to strike out of an entire unit at a time, Space Marines in the Horus Heresy have almost no answer to the Iron Circle in a melee - they must rely on Power Fists, Thunder Hammers and so on to save the day. Lastly, as Battle-Automata, the Iron Circle force successful to-wound rolls caused by both Poisoned and Fleshbane attacks to be re-rolled against them which only adds to the tormenting prospect of trying to kill the mechanical monstrosities.
On the flip side, the Iron Circle somewhat falls a bit flat for raw damage output depending on what they engage; each is armed with a melee Graviton Maul and a ranged Olympia Bolt Cannon, each suited to killing different targets. A single member of the Iron Circle fires five Strength 5 AP4 shots at a range of 36" with the Pinning special rule, essentially working as over-worked Heavy Bolters with the benefit of Shrapnel Bolts but not the downside. With Ballistic Skill 4 these are decent enough at putting pressure on light vehicles and Space Marines when the Iron Circle are fielded in significant numbers, but they certainly aren't that impressive given the price tag associated with the unit - still, anything with a 4+ or worse save will be absolutely obliterated by these weapons and as such they can be seen as a strong tool to use against Solar Auxilia and other less armored forces. Searchlights handily allow the Iron Circle to circumvent the rules for Night Fighting, a handy trick given that illuminating targets normally comes with a drawback - there is no such issue for the nigh-on indestructible Iron Circle.
Melee is an altogether different beast and one that you need to utilize specific characters to really maximize; each model strikes with two Strength 10 AP2 attacks that have both the Concussive and Wrecker special rules, mauling any multiple-wound model with Toughness 5 or less and largely weakening others. These are backed by sadly mediocre stats of Weapon Skill 4 and Initiative 3 making them less ideal for hunting Space Marines and more suited to crushing vehicles or monstrous creatures, solidifying their role as elite hunters up close and infantry suppressors at range; a mere two attacks each renders them rather pitiful at dealing with massed numbers up close. However, there are ways around this deficiency; any sixes to-hit with the Graviton Mauls inflict additional automatic hits on the target which partially alleviates the problem, while the Iron Circle also inflict D3 Strength 7 Hammer of Wrath hits per model on the charge - in that sense, the best way to tarpit them effectively is to assault them rather than be assaulted. In any case, if you send them against anything from Terminators to Hierodules you can expect them to emerge victorious short of some incredibly dicey luck on your opponents' behalf - just don't expect them to cut down swarms of Hormagaunts in quick fashion up close. Frag Grenades do at least allow the Iron Circle to charge into cover with no fear of being slowed down in any ways thanks also to the Move Through Cover special rule courtesy of their Monstrous Creature status.
The Iron Circle can also be substituted for Command Squads specifically assigned to Perturabo in your army list provided the Domitar-Ferrum Battle Automata number four or more models - a hefty investment indeed - and are forced to begin the game in the company of the mighty Primarch. The price of freeing up such a slot is that this particular Iron Circle unit can never be joined by any other Independent Character, but there is a rather significant upside to be gained; this sole unit can choose to freely gain one out of four bonuses, including Weapon Skill 5, Leadership 9, Initiative 4 and Feel No Pain (6+). The only one of these that seems nigh-on useless is the Leadership buff seeing as you should have the Leadership 10 Perturabo with them anyway, while Feel No Pain (6+) offers the barest of improvements to the defensive capabilities of the unit. Initiative 4 Domitar machines can strike simultaneously with Space Marines and many other units but if there is any unit that doesn't need to strike before or at the same time as their opponents, the Iron Circle is one of them - you are best served improving their effective damage output by granting them Weapon Skill 5 and thus the ability to hit most units in the game on a 3+ rather than a 4+.
All that aside, there are several pertinent disadvantages to fielding the Iron Circle that need addressing and the first of these is their position as Battle-Automata. Haywire weapons gain an additional to-wound roll made separately to the standard attack against the Iron Circle while you will lose total control of the unit if there is no model with a Cortex Controller within 12" of them (thankfully Perturabo, Warsmiths, Kyr Vhalen and other such characters all use these). Next, they are tied for the slowest bodyguard in Warhammer 40,000 because they are foot-slogging monstrous creatures with no means of transportation short of attaching a Librarian to them and praying for the Gate of Infinity psychic power. While they aren't slowed much by terrain and they can either Run or pepper enemy forces with their guns, the huge footprint imposed by the unit and the fact that opponents will be scared to death of them will force you to endure multiple turns of advancing before combat can be reached. In the case of Perturabo, why bother with never dying if you can risk his life a little more but have him inside the enemy deployment zone on the first turn via Drop Pod - more of a rhetorical question but an important one nonetheless. Now, as a Tyranid veteran, this unit should theoretically make it into the enemy deployment zone within three turns in most cases provided you Run them at every available opportunity and don't roll badly for that and moving through cover, hopefully setting up a subsequent charge on the third or fourth turns.
In the Horus Heresy specifically, armies tend not to be quite as mobile as you might expect of a Warhammer 40,000 force due to the nature of the Legion list and the focus more on Eternal War missions rather than Maelstrom of War scenarios. Plus, the aforementioned footprint of an Iron Circle unit is large enough that you can easily set up multi-charges into numerous units at a time - with the new grenade rules for close combat, six of the Iron Circle will best forty bare Tactical Marines in close combat without breaking a sweat as an example of why multi-charges don't scare them - and reduce the number of potential escape routes an opponent can utilize. Still, that is a lot of turns featuring the Iron Circle not contributing much to a match - ditto whoever they escort - and what really drives this home is the insane points cost of the unit; at just over two hundred points per model, the Iron Circle are potentially the single most points-intensive multiple-model unit in the game on their own merits, both in the Horus Heresy and Warhammer 40,000. While they can endure several magnitudes above their price the firepower offered by the opposing army, they simply cannot justify that cost in the damage department considering how long it takes them to get to do anything of significant use.
You also have to wonder why you would spend so many points on what is ultimately a bodyguard for a single Iron Warriors character when a squad of Terminators can perform the same role at a much lower cost per model and offer more as scoring units while freeing up points to be invested elsewhere. Crucially, if you want a bodyguard for a character that generally means you want them to get into close combat safely where they can tear enemy forces to shreds; if you need this, speed and durability are your best friends and either a Spartan Assault Tank or some form of Deep Striking are most suited to meeting those criteria. Ultimately, the Iron Circle might be impossibly durable and rather scary in a melee but it matters little when they cost so much and move so slowly that it is almost impossible to ever justify the titanic investment required to use them. They are suited for much larger scale games where their durability will actually matter against the Destroyer weapons being toted by Titans which would normally render your Primarchs' bodyguards utterly worthless, and they aren't devouring a major share of your points limit so that you can still have other supporting elements to an army list. Still, on rule of cool alone, no other Legion has anything on the Iron Circle and that alone is reason enough to use them for more thematic purposes - remember, games set in the Horus Heresy are intended more for narrative-driven games and rewarding the hobbyists that play to the strengths of their Legions. If that is the mantra that your local gaming area follows then the Iron Circle will doubtless work just fine for you and will earn the dual ire and awe of your opponents, but otherwise be sure to extensively study whether they are right for your army list before you include them as they guzzle points like nobody's business.
Thank you all for reading this article, I hope you enjoyed it! As frightening as the Iron Circle are, they don't really match the expectations set upon them by their price tag and instead rank more as an eye-catcher than a crunch-breaker. If you have had the chance to play-test the Iron Circle at all, I would appreciate your opinions on the matter as I just don't see a competitive gem with this unit - of course, that won't stop me from buying six of them once they go up for pre-order as my Horus Heresy adventures are ultimately narrative-driven. Thanks again!