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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 with 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.
All varieties of firearms used by the Military are 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 in 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.
There is a new type of firearm that is used by the Anti-Personnel Control Squad's anti-personnel vertical maneuvering equipment. This firearm has the appearance of a standard pistol that fires a single bullet that is powerful enough to blow off a person's face entirely. The bullets are reloaded in a manner similar to flare-guns used by the regular forces with 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 too in an emergency situation because the hook is located in the user's hands, which makes them very easy to aim. Despite the power of these firearms, the bullets 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.
The nation of Marley and the Mid-East Allied Forces has more advanced firearm technology, which enables them to access to WW1-era firearms like revolvers, Maxim machine gun and bolt-action rifles. However, these modern small-arms do not seems to be any more effective against Titan shifters than the Eldian antiques do, as the Marleyan Public Security Authorities troopers facing Krueger failed to cause any apparent harms upon his Titanized body with their bolt-action rifles before running out of ammunition and getting all killed off. 
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 soldiers within the Military Police Brigade often carry firearms patrolling the Stohess District, particularly shotguns. After Nile Dok accuses Erwin Smith of treason, he and his men threaten to shoot him.
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 used a shotgun "borrowed" from a saloon owner inside a saloon to turn the tables on the squad as they surrounded him. Consequentially, Kenny Ackerman praised Levi after he escaped for using the fact that firearms are legally owned by saloon owners for self defense to turn the tables on his pursuers. Later on, Armin shoots one of the members of the Anti-Personnel Control Squad with a pistol in order to save Jean's life.
- It was revealed after the Survey Corps tortured Djel Sannes for information that the Military Police First Interior Squad is stopping advancements in technology to maintain order within the Walls, with two of the advancements that were suppressed being the development of revolvers and bullet cartridges.