In principle, bullets fired from a gun or rifle behave in exactly the same way underwater as they do above the surface. The oxygen contained in the cartridge is enough to release the shot, but during its trajectory the bullet quickly loses speed and rotation. This means that it drifts off course and sinks to the bottom after just two metres. As water is 800 times more dense than air the bullet is subject to extremely strong resistance. The same principle applies to ricochets, except the water decelerates the deformed projectile even more severely. On ships, barrels of water are used to protect against pirates who might fire bullets at the boat. These liquid shields rob shots of their energy.