A favorite topic of Youtubers everywhere has long been “can you fire a gun underwater?”

Many have proven it can be done, at least once, but in most cases it doesn’t do much but create some cool effects in the water that you can capture with high-speed photography, and send a really slooooow bullet out of the barrel.

However, somebody out there found a practical use for shooting a Glock underwater, and then went ahead and modified the ammo and added a suppressor to make it all work. And yes, apparently the suppressor was very necessary.

Above is a video of divers using a specially modified Glock 17 9mm pistol to dispatch the invasive lionfish in the Gulf of Mexico under 100 feet of water.

Lionfish, which are native to the Indo-Pacific ocean, are particularly dangerous in the Gulf because they eat everything on reefs, including small crustaceans and fish including like the young of commercial species such as snapper and grouper. They have nasty, poisonous quills.

Several states have a bounty on the lionfish, because off the U.S. coast they have no natural predator except for humans who use spears…until now. Most of the people hunt them for money and hobby. Others catch them alive and try to raise them in a home aquarium. Eventho lionfish require a 30 gallon fish tank, aquarists managed to take care of them and raise them in captivity.

In this video, Courtland Hunt explains why he used a suppressor. (Just ignore the fact that the animation repeatedly shows an entire cartridge traveling down the gun barrel instead of the bullet.)

“It is extremely, painfully loud to fire a Glock underwater. I fired the Glock once underwater. It was very painful for me shooting the gun and the people that were with us a good distance away felt like the gun went off in their ear,” he says. “You have to understand that water is not compressible like air.”

He explains that, when the explosion of the 9mm round goes off, the water acts like a piston straight to your eardrum. It’s all about the pressure.

“This is why, in the water, you can feel it go through your entire body,” he says.

“If this was a regular suppressor with baffles on the inside and it’s meant to contain all of the air inside of the suppressor, (the air) wouldn’t go anywhere. You can’t compress the water that’s inside of there, and have it stay there. Nothing would happen at all as the round would go straight through the water as the pressure outside would be the same as the pressure inside.”

Instead, the the underwater suppressor they built basically cycles the gas and the water, allowing the gas to expand outside the suppressor once the projectile exits it.

The suppressor in the video ended up being, what would be on land, a flash suppressor. It’s just a tube with holes drilled in it. It didn’t really work well, they say, until the second chamber was added.

As to how the gun itself functions underwater, you can also see experimenters in the vid painting clear nail polish on the primers of each round to keep them airtight. If they’re factory crimped, there shouldn’t be any water getting to the propellant, which contains its own oxidizer, meaning it doesn’t need oxygen from the air to ignite.

As you can imagine, the lethal distance isn’t that great, at just about five feet, since the bullet has to push its way through water instead of air. But since the divers can approach lionfish very closely, the device clearly serves its purpose—and a Glock is way easier to reload than a spear gun.