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Firearms are weapons that use the combustion of gunpowder to launch projectiles at enemies at high speeds. However, they are unsuitable for dispatching Titans and have not progressed very far technologically within the Walls. Consequentially, they are almost always overshadowed by the vertical maneuvering equipment. However, they are still regularly used by the Military Police and other human-to-human security relations. In addition, their larger cousins, cannons are used as the main line of defense against Titans by the Garrison. The Survey Corps and the Garrison also use flare-guns to communicate over long distances. Since the introduction of human enemies, soldiers have become more inclined to train with firearms in preparation for a human attack.
Firearms used by the military are initially based on the flintlock mechanism, where a piece of flint ignites the powder and fires the gun, which must be reloaded after every shot. Before the reign of Historia Reiss, muskets, pistols, buckshot rifles, hand cannons, and flintlock sniper rifles were the only known firearms to exist for military use. During the battle of Trost, one of the most notable features of the firearm is the lack of smoke it produces which creates a large flash, compared to black-gunpowder which produces a massive cloud of smoke when fired.
Firearms are unable to kill Titans because they lack the power to penetrate through the nape of the neck, the Titan's weak spot. Also, given a Titan's fast regeneration rate and the long amount of time it takes to reload a flintlock weapon (15–30 seconds as they require pouring powder down the barrel and pushing the bullet down with a rod), they are practically useless in dealing enough lasting damage to effectively harm a Titan. However, they can shoot out a Titan's eyes and blind it until it regenerates them.
The Anti-Personnel Control Squad's specialized anti-personnel vertical maneuvering equipment is the first to incorporate firearms with vertical maneuvering equipment. This variant has the appearance of a short, single-barreled shotgun that fires a single shell that is powerful enough to blow off a person's face entirely. Two of these shotguns can be used at the same time. The shotguns are reloaded in a manner similar to signal flares the wielders throwing away the barrels and replacing them with new ones which are stored on bandoliers worn over the wielder's thighs.
Although it is technically not a weapon, the hook can be used as a ranged weapon in an emergency situation because the hook is located in the user's hands, which makes it very easy to aim. Despite the power of these firearms, the shots can be deflected with the ultrahard steel of the standard vertical equipment's sword. Also, their penetrating power is somewhat limited, as Levi was able to block a volley of shots fired at him by using the corpse of a member of the Military Police's Anti-Personnel Control Squad.
By the time Eren Yeager infiltrates Marley, the Survey Corps has incorporated semiautomatic pistols and bolt action rifles into their own version of the anti-personnel vertical maneuvering equipment.
Outside Paradis Island, nations such as Marley and the Mid-East Allied Forces possess more modern firearm technology. Advanced small-arms such as revolvers, sub-machine guns, bolt action rifles and water-cooled machine guns are widely used in those armies. Nevertheless, they are just as ineffective as the Paradis Island's flintlocks when used against Titans, which require the use of specialized artillery such as anti-Titan artillery to defeat it.
During the Battle of Trost, one soldier was shown committing suicide by shoving a musket into his mouth and pulling the trigger. Later on, Armin Arlert conducted a plan to use firearms to blind the Titans inhabiting the supply depot, as the rest of the soldiers would then aim for the nape of their necks, killing them and securing the area.
The Military Police First Interior Squad are revealed to use specially designed firearms in conjunction with vertical maneuvering equipment for their Anti-Personnel Control Squad when they are sent out to attack Levi and the other members of the Survey Corps in an ambush. Later, Levi "borrows" a shotgun from a man inside a saloon to turn the tables on Captain Kenny Ackerman, who chases him inside. After Levi escapes, Kenny grudgingly acknowledges that Levi has gotten better for using the fact that saloon owners are legally allowed to keep firearms for self-defense. Later on, Armin shoots one of the members of the Anti-Personnel Control Squad with a pistol in order to save Jean Kirstein's life.
During the Marley Mid-East War, the rank and file of the Marleyan army is equipped with bayonet affixed bolt action rifles. The Mid-East Allied Forces employ numerous machine guns protected by concrete shelters around Fort Slava, and also equip its soldiers with rifles. Near the battle's conclusion, the Cart Titan, equipped with its Panzer Unit, uses machine guns to rain fire in the Allied trenches.
At the Raid on Liberio, the Survey Corps use anti-personnel vertical maneuvering equipment, modified to fire semi-automatically, to quash the Marleyan armed security throughout the internment zone. Sasha Blouse is equipped with a rifle that she uses to kill numerous enemy combatants. When Marley's Warriors engage the Survey Corps, the Cart Titan's Panzer Unit creates difficulty for the Survey Corps, until its destruction. As the Survey Corps prepare to depart on their airship, Gabi Braun uses a PSA's rifle to kill Lobov, before boarding the airship and also fatally shooting Sasha.
- After the Survey Corps tortured Djel Sannes for information, he revealed that the Military Police First Interior Squad has been stopping advancements in technology to maintain order within the Walls, with two of the advancements that were suppressed being the development of revolvers and metallic bullet cartridges.
- Several guns of Marleyan design resemble real world firearms of the 1920s-40s