Is Water Bulletproof? Separating Myth from Reality

Can diving underwater really save you from a hail of bullets like in the movies? Let's dive into the science of ballistics and water resistance to uncover the truth.

Bullets vs. Water: An Uphill Battle

Firearms are designed to propel bullets through the air, where air resistance has a limited effect. Water, however, presents a much greater challenge. When a bullet enters water, it collides with countless water molecules, rapidly transferring energy and slowing the projectile. Water is roughly 800 times denser than air, dramatically reducing the lethality of standard firearms.

Angle of Entry: A Critical Factor

The angle at which a bullet enters the water significantly impacts its trajectory and distance:

• Shallow Angles (5º-15º): Bullets fired at these angles are likely to ricochet off the surface or break apart upon impact.
• Steeper Angles (above 11º): Bullets have a higher chance of entering the water, but their range is still limited.

Caliber and Velocity: The Surprising Twist

Interestingly, larger, faster bullets don't necessarily travel further in water. High-velocity rounds experience greater resistance, sometimes causing them to break apart. Lower-velocity bullets, like 9mm rounds, can be more dangerous underwater because they decelerate more gradually.

Mythbusters tested this phenomenon, finding that high-caliber bullets essentially exploded upon hitting the water, becoming non-lethal within a few feet. In contrast, a 9mm bullet can be lethal up to 7 feet (2 meters) below the surface.

Shooting Underwater: A Risky Move

Dunking a standard firearm underwater is generally a bad idea. Water can infiltrate the cartridges, preventing ignition. Even if the gun fires, the bullet faces immense resistance, drastically reducing its muzzle velocity and range. Tests have shown that a submerged assault rifle bullet may travel less than a meter before stopping.

Specialized Underwater Weapons

There are specialized underwater firearms designed to overcome these challenges:

• Dart-like bolts: These projectiles move through water more efficiently than traditional bullets.
• Pressurized gas: Some underwater guns use pressurized gas instead of combustible propellants.
• Hydrodynamic design: These weapons often lack rifling, relying on water dynamics for stability.

These specialized weapons, like the Soviet APS Underwater Rifle, can have an effective range of up to 30 meters (100 feet) at shallow depths.

Supercavitating Rounds: A Game Changer

Supercavitating rounds are designed to create a gaseous cavity around the bullet, reducing friction and allowing it to travel much further underwater. These rounds can be accurately fired as far as 60 meters (200 feet), rendering standard aquatic defenses ineffective.

The Verdict: Water Offers Protection, But It's Not Foolproof

Diving underwater can offer protection from bullets, especially against standard firearms. However, specialized underwater weapons and supercavitating rounds can pose a significant threat. It's best to avoid situations where you might need to rely on this in the first place!