Imperial Armour
Imperial Armour is a series of books written by Forge World (the company) to promote their Warhammer 40,000 models. They include full-color drawings, technical data, rules (in some cases full army lists, recently given an official stamp of approval), and, in most cases, a narrative focusing on a campaign which features the models included.
As the name might suggest, there is a bias towards Imperial armies -- at least one of the Space Marines, Imperial Guard, Imperial Navy, Sisters of Battle, and/or Inquisition have been represented in every book, although Forge World does seem to be giving less-seen forces some time in the spotlight, like the Raven Guard, Salamanders, Elysian Drop Troops, and Death Korps of Krieg. However, each book features a non-imperial army foremost (read: on the cover), and releases specialized units, army lists, and Apocalypse love for the specific non-imperial faction being featured. Tau got most of their Apocalypse units from their release, and the Ork list has a whole bloody tactica. More often than not, the xenos even win! Oh who are we kidding - Imperial forces get fucked up in every book - they either outright lose or their victory is totally Pyrrhic. And this IS how you grimdark and show that Imperium isn't alright.
This volume has no over-arching story, though it does offer brief insights into the Imperium, such as tank doctrine and Forge World operations, as well as coloring references and technical data. Most of the vehicles included are Leman Russ variants and artillery pieces that were absorbed into the next Imperial Guard codex (this book was written back in 3rd Edition), and the other vehicles (Baneblade variants, Imperial Navy flyers, and support vehicles) have all been included in later Imperial Armour volumes -- note that this is the only volume not sold by Forge World any more, although a new edition has been released (see below). The "Armoured Battlegroup" army list (featuring Leman Russ Battle Tanks as troop choices!) is introduced in this volume.
Volume Two - Space Marines and Forces of the Inquisition
Again, no big story, but lots of lore about the many vehicles and their variants used by the Space Marines and Inquisition (which includes the Grey Knights and Sisters of Battle -- rather, the Daemonhunters and Witch Hunters, as they were called at the time).
Volume Three - The Taros Campaign
The first Imperial Armour volume with a proper story and campaign, in which the Tau take center stage. The story goes that the desert world of Taros gets investigated by the Administratum, as its tithe and production estimates are out-of-date. The delegation finds that, while Taros is meeting its mineral quotas to the local Forge World, it seems to be mining much more without growing its stockpiles; they discover that the planetary governor has been cutting a deal with the Tau. They enlist the aid of the Avenging Sons Space Marine Chapter, and when that attack fails, the Imperial Guard are called in. They also fail to re-take the planet, and the Tau actually win!
The Tallarn Desert Raiders and Elysian Drop Troops receive rules in this volume, as well as lots of new Tau units (like the mighty Manta, and the Orca from the Warhammer 40,000: Fire Warrior video game). The Raptors also got a little screen time, with some handy illustrations of their color schemes.
Volume Four - The Anphelion Project
The Adeptus Mechanicus decide that it would be a good idea to keep a zoo of Tyranids on Beta Anphelion IV, in order to study them and learn how to fight them better. Contact is, naturally, lost, and so Inquisitor Solomon Lok of the Ordo Xenos gathers up some Red Scorpions and Detachment D-99 of the Elysian Drop Troops to investigate. They learn that the Tyranids adapted to escape containment, Jurassic Park IN SPACE ensues, and the Marines escape while leaving Lok and the Guard to die horribly. Needless to say, this doesn't earn them many brownie points with the Inquisition (*SPOILERS* well apart from the fact Inquisitor Lok becomes a victim of Inquisitorial political back stabbing).
The Tyranids get most of the love in this book, with new biomorphs, Monstrous and Gargantuan Creatures, and big flyers, though the Red Scorpions and Elysian Drop Troops get a few more rules.
Volume Five - The Siege of Vraks - Part One
Vraks, an Armory World close to the Eye of Terror and a key point in the defense of Cadia, falls silent. It turns out that Cardinal Xaphan has taken over, deciding that the Decree Passive was for weaklings, and that he could rid the Imperium of heretics much more effectively by taking direct command. The Imperium disagrees (once they find out about this), and decides that the fastest way to bring Xaphan to heel is with the Death Korps of Krieg. Unfortunately, they weren't counting on Lord Arkos of the Alpha Legion showing up. Still, they manage to crack the first two defense lines, but it seems that Lord Arkos and Cardinal Xaphan aren't out of tricks yet...
The Death Korps of Krieg Siege Regiment gets army rules in this volume (for which we have a tactica), as do the Renegades and Heretics (basically Lost and the Damned for 4th Edition -- Traitor Guard plus Alpha Legion). Some new super-heavy vehicles, the Macharius Heavy Tank and the Gorgon Armored Assault Transport, as well as special siege equipment, also get rules.
Imperial Armour Apocalypse
After years of experimentation (including experimental rules in previous Imperial Armour volumes), Games Workshop releases the Apocalypse expansion for running massive Warhammer 40,000 games. Forge World releases this volume to update the rules on their super-heavies and flyers, as well as include some new formations.
Volume Six - The Siege of Vraks - Part Two
As the Kriegers wear down the final defense line, Arkos summons reinforcements. In particular, lots of Berserkers and Plague Marines arrive, and then the Chaos Titans and flyers come in to attack the Krieg lines from the rear. In response, Segmentum Command sends their own Titan legion and Imperial Navy support, as well as reinforcements for the Kriegers. The Engineers manage to mine and collapse a whole section of the fortress wall, and the Kriegers surge into the gap. Unfortunately, they are held there. The Red Scorpions are asked to help, and they agree, seeing as there are hundreds of Chaos Space Marines to be killed. Though few of the Marines committed survive the assault, they manage to clear the breach and leave it in Imperial control. With the citadel itself in view, the Kriegers prepare to mount their final assault, when Inquisitor Hector Rex shows up and assumes direct control -- it seems that the taint of Chaos is even worse than any had expected...
This volume contains rules for Death Korps of Krieg Engineers and associated mining equipment (like the Hades Breaching Drill), the Red Scorpions, and the "Servants of Slaughter" variant of the Renegades and Heretics army -- basically, Traitor Guard with Khorne stuff. New units include another Macharius variant and the Malcador tank, as well as some updates on rules for Chaos Space Marine vehicles.
Volume Seven - The Siege of Vraks - Part Three
Under Inquisitor Rex's command, the siege around the citadel is sealed tight, and the Kriegers tighten the noose. Unfortunately, the forces of Chaos are hard at work assembling a massive warp portal, and they unleash daemons onto Vraks. The Red Scorpions return, along with some Grey Knights summoned by Rex's urgent missives, and with their support, the citadel's defenses are broken, but not before An'ggrath the Unbound is summoned by the heretics. He gets cast back into the Warp by Inquisitor Rex, and then the Angels of Absolution (successors of the Dark Angels) arrive, to settle the score from Volume Five and take some prisoners. They destroy the leadership, and the Grey Knights clear out the deepest levels of the citadel and finally close the warp portal. In the end, all of the ammunition and stores on Vraks were expended in the siege or destroyed afterward due to Chaos taint, the Ecclesiarchy relics and assets on Vraks were used for Chaos rituals (like a few Sisters of Battle recovered from the dungeons -- they were alive, but given the Emperor's Mercy along with the Chaos Spawn that used to be Cardinal Xaphan) or lost, and nothing was really gained. About the only positive outcome was that the Traitor Titans lost more than the Loyal Titans.
The Death Korps of Krieg get rules for an "Armoured Battlegroup" variant army (Leman Russ Battle Tanks as Troops!), and the Renegades and Heretics get a new "Servants of Decay" variant, as well as some new Daemons and Daemon Engines.
Imperial Armour Apocalypse II
More Apocalypse updates for 5th Edition.
Volume Eight - Raid on Kastorel-Novem
The Raven Guard and Elysian Drop Troops make a raid into Ork-controlled space to try and eliminate a particularly bright Mekboy. It doesn't end well -- after heavy losses, they are forced to withdraw, having failed to locate him (though production is temporarily disrupted).
The Elysian Drop Troops' army list gets updated (see our tactica) for fifth edition in this volume, and the Orks get a new heavily-mechanized list variant, the Dred Mob. This book is where most of the Apocalypse units for Orks now come from.
Email regarding the status of a Second Edition or other update (18/06/15):
Thanks for your question. At this point in time we don't have any information about a 2nd edition of the IA8 book. It may be that we produce a new type of Imperial Armour book covering the Orks in some way rather than an updated version of an older one but we're not sure at the moment.
If you are looking for the rules for our Ork Vehicles then the majority of them can be found in the Imperial Armour Apocalypse book and some of the larger models' rules such as the Gargantuan Squiggoth can be found in the 40k Apocalypse rule book.
Volume Nine - The Badab War - Part One
Lugft Huron decides that he can run his Sector better than the Imperium can. The Imperium disagrees and sends in the Space Marines to put him in his place, starting what would later be called the Badab War. Huron calls in his favors with the other Maelstrom Warders to keep control of the sector, though the Loyalists close in around him.
This volume has rules for the "Tyrant's Legion," forces under Huron's command. They are essentially Imperial Guard with some Space Marine support (or Marines with meat-shields, depending on your perspective and play-style).
Volume Ten - The Badab War - Part Two
The Imperium tightens the noose around Huron, and as his heresies come to be known, his allies start to turn from him. Eventually, the remnants of his forces flee into the Maelstrom. The rest is history.
The centerpiece of this volume is the "Siege Assault Vanguard," a heavy assault Space Marine variant army, including the Caestus Assault Ram as Fast Attack and Ironclad and Siege Dreadnoughts as Troops.
Imperial Armour Apocalypse Second Edition
Enough time has passed that Forge World has to update the rules for old models and release rules for new ones. As a sign of Forge World becoming more "mainstream," this is the first volume to have a "stamp of approval" on its rules.
Volume Eleven - The Doom of Mymeara
Imperial Guard and Space Wolves versus Eldar. The Eldar of Alaitoc and Mymeara, with Corsair support, are looking for the armor of Irillyth, the Phoenix Lord who founded the Shadow Spectres Aspect Shrine on Mymeara (he went out to preemptively eliminate the titular Doom, but never returned). They sense his essence after his millennia-long absence on the ice-world of Betalis III, and fight their way into the manufactory complex to get him, under cover of a massive aerial assault. They successfully recover his armor and re-awaken his spirit. Though Eldar sustain heavy loses during retreat after reaching their goal, so this time its more tie then pure xenos victory as usual.
This volume introduces the Eldar Corsair army list (lots of fast things and flyers, with a complete Tactica), as well as a new Path for Craftworld Eldar Aspect Warriors (the Shadow Spectres) and a new Wolf Lord character.
Imperial Armour Aeronautica
As 6th Edition now includes flyers, lots of Forge World models need to have rules updated (and lots of armies need anti-air support).
Volume One - Second Edition: Imperial Guard
With 6th Edition out the door and no Imperial Guard Codex expected anytime soon, Forge World is releasing an update to Volume One which includes updated rules for all of the tanks and super-heavy vehicles available to the Imperial Guard. The Armoured Battlegroup army list (Leman Russ tanks as troops!) gets an update as well.
Volume Twelve - The Fall of Orpheus
The Orpheus Sector turns out to be home (or, next-door) to several Tomb Worlds, and the Necrons of the Maynarkh Dynasty aren't interested in sharing, especially since they've gotten an especially-nasty case of Flayer Syndrome (which is to say, they like to cut humans up and eat them, despite being robots). The Imperium calls in the Minotaurs and Death Korps of Krieg when all the shit hits the fan, who barely manage to fight them off. By which we means humans were curbstomped anyways, but actually managed to evacuate some forces and dealt some damage in return - before that battle Necrons left no survivers to tell the tale. It should be noted that this requires an epic space battle that shows that Necron spaceships are still just as overpowered as they were in Battlefleet Gothic. Imperials were driven off most of the sector, but managed to keep some ground, and are planning to reclaim their soil in a distant bright future when Imperium wouldn't be in such deep shit as it is now.
The Death Korps gets a new Assault Brigade army list (which is very similar to the Siege Brigade army list, with a number of somewhat-important differences -- see our tactica), whereas the Necrons get the Dark Harvest quasi-army list; it has some changes to units (including Necron Lords and Lychguard), and Flayed Ones can be taken as Troops, but most of the "new" units can be taken for the main book as well. Those new units include the Night Shroud, a new Cronssant with a black-hole bomb; a Tesseract Ark, basically a Catacomb Command Barge that also has a black-hole bomb; the Tomb Sentinel, a new Tomb Stalker variant with a big old gun; and updates for the already-released minis, like the Tomb Stalker and Canoptek Acanthrites. The Minotaurs also get a few new characters.
Volume Three - Second Edition: The Taros Campaign
This volume is received an update to bring the Tau, Elysian Drop Troops, and Tallarn Desert Raiders stuff more in line with the new 6th edition rules. The Elysian Drop Troops also got a new army list in this book, but it's not really that great.
Forge World left in the rules for Tau space vehicles, and even gave them a fancy "Battlefleet Gothic" stamp of approval, even though their Battlefleet Gothic (and other Specialist Games) products had been discontinued. This is especially surprising because the missions that involved other Specialist Games products, namely the Epic and Kill Team missions, were either converted into conventional Warhammer 40,000 games or, in one case, removed.
Imperial Armour Apocalypse (Third Edition)
With Games Workshop updating Apocalypse, Forge World in turn updated the rules of the super-heavies that they make.
Volume Two - Second Edition: War Machines of the Adeptus Astartes
One of the major additions to the new edition of the book is that Space Marines can take vehicles from Forge World's Horus Heresy line -- super-heavies in Apocalypse games or as a Lord of War in Escalation games, and relic Sicaran Battle Tanks, Deimos Predators, Whirlwind Scorpius, and Javelin Attack Speeders in regular games. As a nod to the rarity of the latter vehicles in the 41st millennium, all of these units have the "Relic of the Armoury" rule; a primary detachment of Space Marines can only take one unit with that rule unless a Master of the Forge (or whoever the chapter's equivalent "Keeper of Relics" is) is present, while a secondary detachment only gets to take one if it's being led by a Keeper of Relics.
Volume Four - Second Edition: The Anphelion Project
Relatively similar to its original counterpart, but it adds some more characters to the Red Scorpions, an army list for Detachment D-99, rules for Zone Mortalis games, and revised rules for the FW Tyranid superheavies, including a new unit in the Dimachaeron (think a bigger, uglier Lictor).
Volume Thirteen - War Machines of the Lost and Damned
Volume 13 contains updated rules for Chaos Space Marine equivalents of loyalist vehicles (including those introduced in Forge World's Horus Heresy products), daemon engines, and Chaos Titans. It also updates the Chaos Renegades lists introduced in the Vraks trilogy (we have a tactica). In fact, they also sell a bundle of this volume with volumes 5, 6, and 7 for just 30 pounds more than IA13 itself. They say it's so that Chaos players can get the full history (and full campaign rules) of the Siege of Vraks, though it's probably also to shift the last of their Vraks books now that they are fully superseded.
The Siege of Vraks
An unnumbered volume which combines the lore from all three Siege of Vraks books and contains Vraks-specific characters, units, and army rules for the Death Korps of Krieg and Renegades and Heretics. (Presumably, it was left unnumbered because calling a book "Volume Five, Six, and Seven - Second Edition" would be silly.)
The Doom of Mymeara
Another unnumbered volume, though unlike with Siege of Vraks, removing the number was strictly unnecessary as the original book only consisted of one volume, so its really just an update rather than a consolidation.
It provides revised rules for pretty much everything in the original volume, bringing the standard up a considerable notch. Rules for all of the special characters were redone for better or for worse, and the Eldar Corsairs were given a massive overhaul without making them into something unrecognisable.
Rules were also given for all of Forgeworld's Craftworld Eldar gear, and one brand new addition that wasn't in the original was rules for customising your own Craftworld, giving you a formation that let you choose your combination of traits.
Fires of Cyraxus
An upcoming volume, also unnumbered because apparently GW lost count of how many IA books they've made now. Adeptus Mechanicus and Red Scorpions vs Tau. Expect a lot of rock-em sock-em robots as the 30k Cybernetica Automata go up against the new Tau Battlesuits. Including new rules for Secutarii (Skitarii) and what looks to be an update to the Taros campaign Tau rules, as well as Red Scorpions Chapter Master Carab Culln being turned into a Leviathan Dreadnought, giving him officially more rules than any other named GW character ever (with a whopping four different versions of him).