One of the things movies always get wrong about firearms is how water will affect the way a bullet travels. Even in the otherwise-almost-too-real “Saving Private Ryan,” bullets are shown flying through water almost exactly as they do in the air: on a straight trajectory and with a lethal amount of kinetic energy. The truth of the matter is, bullets just don’t move through the water all that well. In fact, with many firearms, all it takes is a few inches of water to strip a moving bullet of the speed necessary to penetrate the human body. In most cases, water just knocks bullets off their course, but in some, hitting the water is enough to break the round apart completely. While some firearms can function under water, they tend not to function as you’d need them to if you were in a fight for your life.

This scene from John Wick 3 actually does a really good job of demonstrating how water affects bullets.

(Warning: graphic content)

For most folks, a weapon’s ability to take a life while completely submerged in water isn’t a pressing concern, but for some very specific groups of war fighters, this presents a serious issue. Navy SEALs are known for conducting clandestine operations in and around the water, and Navy Frogmen are often tasked with preventing the foreign equivalent of our SEALs from doing the same near American shores. Because most standard issue firearms would be all but useless in an underwater engagement, these undersea war fighters needed something with a bit more reach than their diving knives that actually worked beneath the waves.

That’s where Heckler & Koch stepped in. Back in 1976, they secretly developed the P11: a five-barrel module-arrangement pistol that’s capable of firing 4-inch long steel darts. Its effective range underwater was between 30 and 50 feet (depending on depth) and they could even be fired in the dry air with an effective range of just shy of 100 feet (though accuracy was said to be questionable at such distances).

Heckler & Koch P11 with test-device (WikiMedia Commons)

H&K didn’t even acknowledge producing the pistol until 1997, giving their select customer list a solid two decades of use before letting the cat out of the bag. According to some sources, hundreds of these pistols were issues to Naval special warfare units, though it’s unclear how many are still in service. It stands to reason that the Navy may now be operating more effective underwater weapons.

Instead of using traditional rounds, each of the five barrels came sealed from the manufacturer with what was effectively a mini-rocket propelled missile stored inside. The projectiles were actually tiny solid-fuel rockets with fins to stabilize their path as they sailed through the water. When the operator pulls the trigger, an internal battery actually sends a current to ignite the fuel and launch the projectile through its barrel. Once all five rounds had been expended, there was no way to reload the pistol — it had to be sent back to Heckler & Koch to have a new sealed five-round chamber installed.