Legion Arquitor Bombard
"With its reinforced chassis and brutal short-range firepower, the Legion Arquitor Bombard is called upon to break the most stubborn enemy fortifications or annihilate massed troops and armour. Deployed alongside infantry squads, the Space Marines know that these artillery pieces will see them through the most ferocious of firefights."
- – GeeDubs description.
With its small size, the Legion Arquitor Bombard could only mount weapons as big as it is, as such, as such the range of these weapons are cut pitifully short, especially for a dedicated artillery piece. Fortunately, the weapon that the Arquitor is armed is the aforementioned graviton beat stick, a big cannon, and the Spicula Rocket System.
The graviton-charge cannon is the but one primary weapon option of this little 4HP artillery tank, in classic FW fashion they previewed this option first before actually releasing it out of the blue with a totally different weapon option — the unfortunately named Spicula Rocket System.
Rockets are used to clear infantry formations, whilst presumably the grav weapon is used to crush enemy fortifications and the occasional tank in times of heavily drawn-out sieges. Seeing as how graviton and other grav weapons are for more effective against objects that are extra THICC such as vehicles, super heavies and TEQs, blasting a graviton wave against a giant wall seems to be the next logical conclusion. Walls have to be big y'all to be truly effective, so it makes sense to use the wall's very own size and weight against it; stressing the foundations until the wall itself could no longer take the amplified weight before crumbling down like the Berlin Wall.
The Morbus Heavy Bombard is a big fuck-off cannon able to wreck even the most heavily armored of enemies. Apparently old Morty was impressed, because its cannon looks just like the one on his Plagueburst Crawler daemon engines.
Unfortunately, the short range of its primary weapon options kind of makes this baby Minotaur a bit too risk-heavy and, given how rare and expensive Grav-Weaponry are, present day Space Marine Chapters which still house these artillery pieces are quite hesitant at rolling them out in the battlefield. The vehicle is mounted with option two heavy bolter or two Autocannon sponsons as secondary weapons.