Ordinatus
"A weapon the size of a Titan. A near-perfect expression of the Omnissiah's grandeur and, of course, his puissance. Armies are thrown to the wind by its glorious song, and mountains themselves skitter aside at its demand. Nothing stands before a sacred Machine Spirit so mighty without its consent."
— Tech-Priest Garrulon Vyme, on an Ordinatus
In the rare event that even the Titan Legions just can't get the job done, the Imperium of Man brings in the specialized war-machines known as the Ordinati.
Overview
Unlike the standard Titans, each Ordinatus is custom-built by the Adeptus Mechanicus for a specific objective and named after the world it was constructed on. A special branch of the Admech called the Centurio Ordinatus is responsible for their creation, use, and maintenance, similar to the Collegia Titanica. The Ordinati themselves vary widely in armaments, size, shape, and role- some are armed with guns that would make an Imperator Battle Titan jealous, others are designed to carry entire battalions of troops, but all are more than capable of winning a war on their own. Most of them are only used for one battle and then get mothballed.
It seems kind of wasteful given how stupidly powerful they're supposed to be, but you must first realize how the Mechanicum sees them. To the AdMech, innovation is one of the most dangerous things in the galaxy - if they invent a new Ordinatus it is only out of extremely dire need, and even then only the Centurio Ordinatus Magi are entrusted to do so. After it fulfills its purpose, the new Ordinatus should by all means be left alone unless it needs to perform its specialized role again. After all, it's a new technology, and as such using it without a very, very good reason is seen as sacrilege if not outright tech-heresy.
In light of that, actually deploying one at all is a very rare event compared to that of their Titan counterparts. Most of them were either destroyed, lost, damaged beyond repair, or just plain forgotten during the Horus Heresy. They're typically deployed separately from any Titan Legions or Skitarii, and are used only when any other options have failed.
Ordinatus engines are absolutely massive land crawlers that can run over and squash Baneblades, and are protected by a specialized energy field called a Dispersion Field on par with a Titan's void shields. Unlike the titans, Ordinati are usually not meant to directly assault enemy positions, but tend to be better suited as really big back-line artillery - they are (very relatively) squishy for their firepower and most times indiscriminate at unleashing said firepower, so they need support armies to keep enemies at distance as they blow everything within several hundred miles of them to pieces.
Speaking about firepower... While Titans and huge ass super heavy tanks tend to have multiple guns on them, Ordinatus engines always mount only one ridiculously OP weapon system which can be as large as an actual Titan. Most (if not all) of those systems were once specifically designed to solve one particularly difficult problem. Let me reiterate this: The Mechanicum, the guys who see innovation as one of the most perilous things in the galaxy, actually invented things. Not just "in the distant past before much knowledge had being lost" but right the fuck NOW - some of the famous Ordinatus weapons were invented in M41 to fight off Waaagh! Ghazghkull. It's no surprise to anyone that the cogboys consider them the most sacred relics that they possess.
Ordinati Minoris
The "small" Ordinati, which are still each the size of three Leman Russ tanks lined up end-to end and are typically armed with weaponry normally seen on Titans. They're easily recognized by the four sets of tracks they possess- two at the front and two at the rear.
Forgeworld have made a model of this for the Horus Heresy line.
Ordinatus Mars
During the Schism of Mars, one traitor Magos holed himself up in a mountain citadel, sending his armies to harass Loyalist factories. Four companies of Imperial Fists led by Sigismund were sent to stop him, but discovered that the Magos possessed a peculiar xeno artifact that caused any ship that got too close to it to be blown up or thrown into the Warp. A ground attack was decided to be a more viable approach...if it weren't for the half-mile thick walls made of the toughest materials known to the Imperium.
The Mechanicum responded by creating the Ordinatus Mars, armed with a Sonic Disruptor that caused the citadel to shake itself apart with the force of its sound waves. As the walls of the fortress crumpled the Loyalist Tech-Guard was able to storm the citadel and execute the traitor Magos with no difficulty.
Ordinatus Golgotha
After Ghazghkull Mag Uruk Thraka fled Armageddon, Yarrick managed to track him down to the planet Golgotha. Some time after his capture by the greenskins and later escape, he returned with a punitive force of Titans and Skitarii. The sheer size of the Ork WAAAGH! made it impossible for them to gain an advantage, warranting the creation of an Ordinatus made specifically to deal with overwhelmingly massive hordes.
The Golgotha's Hellfire Missiles were perfect for the job, and routed the Orks within a week. Since then it's been deployed in any battle where the enemies of the Imperium outnumber even the Imperial Guard.
Ordinatus Armageddon
The Ordinatus Armageddon was designed during the First War for Armageddon to defend against a particularly dangerous horde of Daemon Engines. The plasma-based cannon gives it the ability to melt Titans in one shot and disintegrate entire tank battalions with a salvo. Supposedly, it was inspired by an old Squat anti-Titan vehicle. The book Helsreach speculates that the Ordinatus Armageddon's main gun was basically a Nova Cannon (a weapon typically used only on Imperial Navy warships) modified to use an auto-loading system instead of a crew of thousands of slave workers.
Ordinatus Priam
Essentially the Hades Breaching Drill's big brother, the Priam was designed during the Siege of Priam to bypass the defenses of an occupied city by drilling directly through a planet's crust, travelling through the mantle underneath, and then reemerging behind enemy lines. It was successful at deploying four companies of Imperial Guard to break the aforementioned siege without incinerating them in the process, but was rendered inoperable afterwards due to its shielding partially failing during the attack.
Ordinatus Gehenna
The Gehenna was armed with an Apocalypse Cannon strong enough to shoot straight through a planet's crust hard enough to trigger magma flows. It was fought over by the Imperium and Chaos during the 13th Black Crusade.
Ordinatus Volcanis Ultor
A rare example of a Traitor Ordinatus, made by the Dark Mechanicum of Volcanis Ultor to wipe out an advancing force of Grey Knights. Its exact armament was never described, but judging by the description of it being able to fire pinpoint salvoes of multiple warheads it may have been capapble of firing missiles or shells of some kind. However, it was never actually used- the wreckage of a Grey Knight Strike Cruiser that had just been destroyed by the traitors' warships crashed on top of the war machine, obliterating its cannon barrel and ammunition loading systems by accident.
Gallery
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The Ordinatus Armageddon, for when you really need a continent bathed in plasma. -
The Ordinatus Golgotha. How do they reload those missiles, anyway? -
The Ordinatus Mars. Suck on it, Noise Marines.
