In real life, when looking into the water, or out of the water, at an angle, the difference in index of refraction between water and air causes objects in the other medium to appear to be at a different angle relative to the viewer than they actually are. This makes it particularly difficult to shoot into or out of water and hit your target. Currently, this effect is not implemented in game, which means that one could shoot the pilot out of a low flying helicopter fairly easily while still submerged.