In Real Life, most guns will jam or misfire when people discharge them underwater. It's not the gun itself that is affected (well, not for the first time, anyway) — it's the ammunition itself. Even if the gun is somewhat water-resistant (and that's a big somewhat, given that the barrel of a gun is essentially a giant hole), the primer of the ammunition is not. Besides the possibility of the primer being waterlogged, the gun's inner workings could also end up corroded by the water, and attempting to fire a corroded gun is a Very Bad Idea.
A gun may work one or two times when fired underwater, but in the long run, water will seep into the gun or wet the crucial parts of it, making it completely useless. And then there's the actual water pressure itself, which means the bullet won't go very far.
However, there are some guns that have been designed to work underwater. These include the Heckler and Koch P11 pistol and the APS Underwater Assault Rifle.
Also a case of Do Not Try This at Home, because guns are not intended to be fired underwater. Shooting a gun filled with water or wet ammunition is probably not going to end well for you or anyone around you. And shooting a gun underwater with air in its barrel is even worse, because the gun can explode.
Subtrope of Water Is Air, because the bullets will still work fine — though they just won't travel very far. Spearguns designed for fishing underwater are also common in the hands of divers and underwater Mooks.
Examples:
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Anime & Manga
- In Black Lagoon, Revy gratefully takes an APS Underwater rifle from Balalaika, who used her military connections to the newly restructured Russian military to acquire it. She notably uses it during the Das Wieder Erstehen Des Adlers/Die Rückkehr des Adlers story when the APS is used against Aryan Socialist Union forces raiding a wrecked U-Boat.
- One of Leiji Matsumoto's short war stories depicts what happens when a rifle is waterlogged. A Japanese soldier, having been rescued from the sea, shoots the sole surviving crewman of a recently destroyed American submarine that sank his transport ship. The Japanese rifle, having gotten seawater down the barrel, manages to spit out the water along with the bullet. The bullet is slowed down by the water and only gives the intended victim a nasty bump on the head. To the credit of the Type 99 short rifle in question, the barrel's chrome-lined bore doesn't suffer any corrosion.
Comic Books
- In Jon Sable, Freelance, Jon's .357 Magnum pepperbox — a Swiss-Army Weapon — can fire underwater; usually firing steel spikes like a miniature spear gun. Justified as this is a gun specifically designed to fire underwater, being based on a prototype weapon designed for the Navy SEALs.
Film — Live-Action
- John Wick: Chapter 3 – Parabellum: John Wick and a Mook fall into a pool during the battle of the Continetal. The mook tries to shoot Wick, but the bullets do not reach him and he shoots the mook point blank instead.
- Jurassic World: Fallen Kingdom: Claire and Franklin are trapped in a leaking "hamster ball" under water. Owen fires his gun at the ball to help them escape, and it actually works until he gets hit by a blob of lava and drops his gun.
- In the opening action scene of Lara Croft: Tomb Raider – The Cradle of Life, Lara is attacked by rival tomb raiders in a sunken Greek temple. The raiders are armed with Harpoon Guns, while she fights back with a Heckler & Koch P11, a pistol designed to fire underwater.
- Lethal Weapon 4: Martin Riggs kills Wah Sing Ku by shooting him point blank with an assault rifle after throwing him into the water.
- In the 1983 thriller Love is Forever (aka Comeback) the protagonist is swimming using scuba equipment across the Mekong River into Laos when he's spotted by a patrol boat who open fire with a machine gun. Underwater shots reveal the bullets scatter wildly after they hit the water and he's able to dive beneath them. Then they start throwing grenades...
- In the climactic fight of Mindhunters, the heroine and the Serial Killer Big Bad both pack Glocks and both shoot at each other while struggling underwater, but while the Glocks shoot all right, the bullets just lose all of their velocity the moment they leave the barrel. The two of them are then forced to keep the guns out of the water and the fight then becomes a test to see who can hold their breath the longest, with the stakes of the loser being shot the moment they have to emerge.
- Shoot to Kill. FBI Agent Stantin shoots the killer during an underwater struggle at point-blank range, avoiding the bullet diversion problem.
- U.S. Marshals: While a pistol is not actually fired underwater, Sam Gerald makes mention of Glocks being capable of doing this as one of the reasons he loves his sidearm.
Live-Action TV
- Tested by the MythBusters. Even if a gun does fire, the water will slow a bullet down to nonlethal speed in short order.
Tabletop Games
- In Blue Planet, most modern guns use electrically-ignited binary propellants and work just fine underwater, or can be made to with a minimum of fuss. (Corrosion's a problem, but it happens on land too.) That being said, water pressure does horrible things to external ballistics; range penalties pile up fast, on top of a penalty for being underwater at all.
- Pathfinder: Firearms can't be used underwater unless protected with specific magic, and even then, shooting through water imposes a stiff penalty on the weapon's accuracy. Early ammunition is ruined outright by exposure to water.
- Shadowrun: Averted, as there are rules for how bullets work underwater (generally, they don't) and there are a few weapons that have been specifically designed for underwater combat, including a carbine.
Video Games
- Alter A.I.L.A.: In the Underwater Facility, you can fight enemies while underwater, and the battle screen doesn't reflect the battle being under water. This means that you can use all the regular weapons that you'd be able to use normally, like Shotguns and such.
- In Call of Duty: Ghosts, Logan starts of the underwater missions "Atlas Falls" and "Into the Deep" with the APS Underwater Rifle.
- In Cave Story, all the firearms you can acquire fire underwater just as well as out of water.
- Death in the Water has the krakken, an underwater shotgun which is a high-tech piece of hardware meant to function in the deepest trenches.
- Delta Force's standard guns won't fire underwater, which is a nice touch considering how little time players will actually spend swimming. The second game introduces a pistol and an assault rifle specifically for underwear combat, but they're notably inferior to standard guns.
- Deep Black Reloaded is a third-person shooter that's mostly set underwater, and all your guns fire effectively without any problems in the abyss.
- Guns won't work underwater in Deus Ex, so you'll want a melee weapon for dealing with critters in the sewers.
- Half-Life: One of the advantages of the Glock (the game's starting handgun) is the capacity to fire underwater. It is one of only three weapons (the others being the crowbar and the crossbow) that can be used in such scenarios, and this characteristic carries over to its equivalent in Half-Life 2, the USP Match.
- In the Water Levels from Jazz Jackrabbit (Lagunicus in the first game and Marinated Rabbit in the second), all of the weapons successfully work underwater, including the fire bullets, without getting slowed down.
- The Legend of Zelda: Spirit Tracks: The train's weapon is a large cannon, but deals with underwater segments by firing torpedoes instead.
- Metal Slug, from 3 onwards, introduces underwater levels, and all your weapons works fine while you're beneath the surface. You don't get the Flame Shot in underwater stages though, but it's still possible to die via Man on Fire even in such stages.
- In Might and Magic VII, the closest thing to a gun is the only weapon that can be used underwater, though being Lost Technology Ray Guns it can probably get away with it (it is a bit more odd that you can't use spears). Conversely, the underwater area in VIII imposed no restrictions at all, but being the Elemental Plane of Water it isn't quite working on the same rules as normal water to start with.
- Player Unknowns Battle Grounds: The player can swim through the water and their guns can fire as though nothing happened.
- In Red Ocean, your guns can't fire underwater (though underwater areas never contain enemies) and as you surface in areas with enemies, your firearms can somehow work perfectly without clogging issues, despite being underwater literally seconds ago.
- : All the guns in Sea of Thieves fire perfectly fine underwater, made more egregious by the fact that they're all powder weapons and shouldn't even be able to fire because the ammo is wet.
- Super Robot Wars: Most of the mechs' projectile weapons work underwater regardless of how these actually function in the canons of the works that are crossing over. Gameplay and Story Segregation applies, of course, but sometimes these can also be handwaved by the Minovsky Physics or Magitek involved with a particular series. Subverted because, depending on the installment, there might be some penalties to the damage output and/or accuracy of these weapons based on their terrain ratings (Gundam beam weapons in particular used to deal nothing but Scratch Damage if used underwater, though later games buffed them to a more standard damage reduction). These ratings can be improved through upgrades, ace bonuses, or items, if these features are present.
- Team Fortress 2: Many of the weapons will work underwater, except for Pyro's flamethrower, and the flare gun.
- Terraria: Multiple types of guns can fire underwater with no difficulties. Flare Guns can fire underwater fine, as can the minishark, which fires musket balls.
- The archguns in Warframe are a class of firearms so massive that without a Gravimag device installed they can be wielded properly only in freefall... or underwater, where they work just as fine as in space. The Grineer underwater forces are equipped with Harpaks and Kulstar handheld torpedo launchers, two types of guns designed for use underwater which the Tenno ironically can only use on dry land.
- Justified in X-COM: Terror from the Deep. Since most of the fighting is done underwater, the X-COM soldiers use weapons specially designed to be used underwater. Some weapons only work underwater (for example, the torpedo launcher), while others work both under and above water.
Western Animation
- Not conventional guns, but in Star Wars: The Clone Wars blasters are shown being used underwater during the Battle of Mon Calamari, as are lightsabers. Somehow the energy doesn't dissipate into the water until it hits a target.
Real Life
- While dedicated underwater weapons have been developed as noted below they have never been used in combat, as the odds of two groups of divers encountering each other is almost nonexistent. Most potential targets have anti-diver defenses mounted on the surface, using everything from high powered sonar and dolphins
to concussive grenadesnote , while divers themselves are more or less guaranteed to be killed if they are found and so few of them really bother to carry weapons for such a niche purpose.
- The Soviet APS underwater rifle is an assault rifle designed for underwater combat, firing steel darts that resemble those fired by a Spear Gun. It was originally designed for the use by divers guarding important underwater infrastructure, after NATO successfully tapped underwater telephone cables carrying military comms and prompted the Soviets to start having their own frogmen carry out patrols. It was also issued to Spetznas for their own combat diver teams, but they quickly discovered it suffered from Crippling Overspecialisation: Out of the water its range and accuracy were poor. The ASM-DT amphibious rifle and AFM-DT carbine, which could fire the same darts as the APS but also load standard 5.45x39mm bullets, was developed to meet demand for a dual-purpose weapon. Later the ADS Amphibious rifle was developed which could use both standard 5.45mm ammo as well as special 5.45x39mm M74 7N6 cartridges meant for firing underwater.
- Underwater firing pistols have also been developed, the most popular being the Soviet SPP-1 underwater pistol and the Heckler & Koch P11. The SPP-1 has four shots and can be reloaded via clips that hold its 4.5mm cartridges together, while the P11 uses a pre-loaded five round cylinder that must be replaced by the manufacturer in order to be reloaded. Pistols are often preferred because they waste less space for such a niche weapon.
- Some people just had to try firing ship-board artillery underwater. Unsurprisingly it didn't work, but the idea did lead to the far more practical concept of the torpedo.
- There was a news item making the rounds in 2016 about a Florida fisherman (of course) who used a Glock underwater to fish. Of note for the purposes of this trope: While the gun could fire multiple shots after some slight modification (apparently, all that needs to happen is the firing pin needs to be cut to allow to allow water to flow behind it and the springs are probably going to need replacing a lot sooner), he had to use a special (underwater only) sound suppressor, as the sound waves became sufficient to impact the shooter underwater, particularly with repeated shots.
