|While we've been relying heavily on Titans and colonial expansion, other nations have been developing weapons to counter us. As a result, our strategy has come to bite us on the ass.|
|— Commander Theo Magath deduces the origin of Anti-Titan artillery|
Anti-Titan artillery was created for the purpose of destroying Titans of all varieties with great efficiency. It fires 150mm shells, and the armor-piercing type of which has enough firepower to kill even the Nine Titans, such as the Armored Titan and Beast Titan, with a single shot. Besides killing Titans, the gun was also used in normal bombardment missions in which it fired fragmentation shells.
During the battle of Fort Slava, four anti-Titan artillery guns are mounted on an armored train surrounding the fortress, allowing for great mobility on the battlefield. However, the guns were more commonly mounted in field gun carriages. At least 28 guns in the latter configuration were deployed on the fort's wall, forming the main barrage ring of the Allies' defender.
Even when fitted on a field gun mount, the anti-Titan gun was very maneuverable, being able to turn about quickly by a crew of four to face threats behind it. For example, the guns managed to score a few hits against a fast-moving Armored Titan, and were able to react effectively against the mindless Titans landed inside the fort. However, it was not without its weakness. The gunners still have to land an accurate shot on the approximate area of the nape of the neck for an effective kill. The gun also has a limited degree of depression, as the field guns on the fort were unable to fire upon the Cart Titan and Jaw Titan who were outside the wall, but the standing Titans inside the fort were within range.
Although the gun was said to be a new weapon, its sizable number and different variants may suggest that the Allies mass-produced the gun in such quantity that it became the Allies' standard field artillery piece by the time of the battle.
Anti-Titan artillery makes its debut in the Marley Mid-East War during the battle of Fort Slava, where it is mounted on an armored train traveling along rails surrounding the perimeter of the fortress. The presence of the weapon prevents the use of the power of the Titans possessed by Marley, drastically reducing Marley's ground-based power. However, the armored train and its anti-Titan gun turrets are both rendered unusable when Warrior cadet Gabi Braun destroys its lead car with a bundle of grenades, allowing for Galliard to make use of his Jaw Titan power and directly attack the Mid-East Allied Forces' defenses.
After Titans are airdropped into the fort, the field guns remaining on the fort attempt to put them down, but are stopped by the Armored Titan. Although the Armored Titan succeeds in destroying all the guns by sweeping them apart with an armored train which it uses as a club, the damage it sustains alert him of the unprecedented lethality of the new weapon.
After the war ended, the Marleyan military was able to acquire the guns for their own usage. While inexperienced, they were able to use them to hinder the Attack Titan's movements against the War Hammer Titan before the guns became targets for the Scout Regiment and their re-purposed Thunder spears.
An anti-Titan artillery gun was airdropped alongside with Marleyean forces during the Paradis Island Surprise Attack, this time being mounted upon the back of the Cart Titan and being operated by Theo Magath and Koslow. The three were able to destroy the Attack Titan's motor skills, allowing time for the Armored Titan and the Jaw Titan to break free from the Attack Titan. Improved upon from Mid-East technology, the Marleyan anti-Titan gun was designed to destroy the Founding Titan and penetrate even through hardening.
As Zeke and Eren try to make their way to the other, Eren notices out of the corner of his eye that a tearful Gabi has picked up an anti-Titan rifle. Before anyone can react, she shoots a round into Eren's neck, decapitating him.