Crassus Armored Assault Transport
Named for Borgen Crassus, one of the leading generals of Lord Solar Macharius, the CRASSUS ARMOURED ASSAULT TRANSPORT, aka the Mark IX Tank IN SPAAAAACE!, is one of the heaviest armored transports available to the Imperial Guard. Armed with a quartet of heavy bolters and capable of lugging 35 of your t-shirt wearing maniacs/über badasses around the battle field, the CRASSUS ARMOURED ASSAULT TRANSPORT is essentially the Guard Landraider but with fewer guns.
Based on the chassis of the Macharius Heavy tank, the CRASSUS ARMOURED ASSAULT TRANSPORT is the perfect vehicle for carrying large amounts of Guardsmen directly into enemy fire and dropping them off exactly where you need them.
Even though the CRASSUS ARMOURED ASSAULT TRANSPORT is a relatively new addition to the arsenal of the Imperial Guard, it has already become famous for its heavy armor and firepower, and has entered widespread use in the southern and western regions of the Segmentum Tempestus and after only a few centuries the CRASSUS ARMOURED ASSAULT TRANSPORT design is now being constructed on the Forge World of Lucius and is used to extensively resupply the Imperial forces that are guarding the space around the Eye of Terror to replace the on-going losses in that steadily worsening warzone.
There, as everywhere else it had been deployed, the CRASSUS ARMOURED ASSAULT TRANSPORT had earned a considerable reputation for its sheer power and durability. This reputation has given the vehicle near-talismanic status amongst some siege assault units of the Imperial Guard, to the concern of some within the Commissariat and the Departmento Munitorum. The Tech-Priests probably wholly approve, though. Yes, wholly is a word and is spelled correctly.
In case you were wondering, some fellow asked about whether it'd be worthwhile getting the CRASSUS ARMOURED ASSAULT TRANSPORT, which they wrote in all caps because they just copied that from Forge World's product list wherein everything is listed in all caps. Memes of course, ensued. Most likely because the name is so long that it really is easier to just copy-paste it and since the first person to do that pasted all caps...and also to needle him for the caps, of course. Still, DorianGray, the Original Poster, is now one of the few and the proud who created a new meme.
Praetor Armoured Assault Launcher
Much as the Chimera was modified into the Manticore Rocket Launcher by ripping out the troop compartment and bolting a missile launcher to the top, the PRAETOR ARMOURED ASSAULT LAUNCHER mounts a massive Praetor missile launcher instead of a transport bay. It can launch Foehammer missiles for cracking armor, Firestorm missiles for blasting large infantry formations, or Pilum (Latin, "Javelin") missiles for anti-air defense. Which is silly since javelins were created to kill infantry. Although, hammers are good against armor and everyone likes killing things with fire, so it all works out.
Considering that the PRAETOR ARMOURED ASSAULT LAUNCHER has no limit on ammunition (during the game, anyway), a comparison to the Rhino-based Whirlwind might be more suitable. But infinitely more awesome and in reality would probably be radically more deadly.
However, due to the vehicle's complexity, it has not been as widely distributed as the more basic CRASSUS ARMOURED ASSAULT TRANSPORT. Servos to rotate something up and down (extremely common in much Imperial technology and is incredibly cheap even in real life) is, after all, incredibly complex (it's an electromagnet, so this is sarcasm). Seriously, the AdMech is just being an ass here for the lulz. While the PRAETOR ARMOURED ASSAULT LAUNCHER'S sophisticated systems and relatively high materiel cost makes it unlikely to replace or supplant the existing Imperial designs for mobile rocket artillery pieces, its durability and sheer versatility have already ensured it a valued place amongst those Imperial Guard units facing the most deadly adversaries of the Imperium. Which implies if the AdMech stopped pretending it was difficult to make (ten bucks says the guidance system is the same as every other Imperial rocket artillery) and spams them, said most deadly adversaries would be fucked.
An interesting trivia is that the design for the Praetor Heavy Assault Launcher actually predates the introduction of the CRASSUS ARMOURED ASSAULT TRANSPORT and it is believed that the last time the PRAETOR ARMOURED ASSAULT LAUNCHER' saw widespread use by the armed forces of Imperium was against the Land-Leviathans deployed by the Tellarite Rebellion forces who had forged their a pocket-empire in their little corner of the galaxy during the dark years of the Nova Terra Interregnum. Apparently not even those things could resist the might of the Macross Missile Massacre. Still, the fact they saw wide-spread use at all implies the whole "it's too complex to see wide-spread use" is a fucking lie. As usual, anything that would allow the Imperium to kick ass (or often enable the Imperium to outright win the Eternal War just with that one thing) is not allowed to be used by almost anyone. Because the Imperium is the true defender of the status quo by virtue of murdering their own brain cells whenever something cheap, useful, and easy to mass-produce comes along.
Dominus Armoured Siege Bombard
Another variant of the CRASSUS ARMOURED ASSAULT TRANSPORT the DOMINUS ARMOURED SIEGE BOMBARD replaces the troop transport capability with a massive Dominus Triple Bombard. This turns it into a dedicated artillery piece that can rapid fire due to its automated weapon system and the fact that it carries not one, not two but THREE enormous mortars, meaning that it can devastate entire blobs of armies in a single phase. It's the Wyvern's bigger, angrier brother with a criminal record.
In practice the DOMINUS ARMOURED SIEGE BOMBARD throws 10d6 S10 ap-3 shots with indirect fire when stationary, easily wiping any unit foolish enough to be larger than 5 models. S10 Ap3 is also a serious threat to any armour short of a titan, and the weight of shots pretty much guarantees an overkill of single model targets. Think of it as an entire battery of Basilisks in one vehicle, except for less points, with better armor, no Open-Topped bullshit, and a pair of sponsons to defend itself.
One final point of delight in this things favor comes from how overwatch works - not only does it get to fire everything it has at anything that charges it (which will frequently paste dreadnoughts even hitting on 6s) but can simply drive out of combat and keep shooting thanks to its Steel Behemoth ability.
Despite having had rules released for it in the 8th edition overhaul, the DOMINUS ARMOURED SIEGE BOMBARD doesn't actually have an official model. So expect a lot of fan conversions like the image on the right.