If the water drag is eliminated, the sub’s top speed will suddenly be multiplied – and that is exactly what supercavitation is about. Supercavitation can be observed when a projectile is shot through water. At first, the projectile will drag an air bubble along from the surface. If the speed is sufficiently high, and the projectile is shaped in a particular way, it can continue through the water surrounded by the air bubble. The US Navy has already developed projectiles that take advantage of supercavitation, but unfortunately, the air bubble is dissolved after a few seconds, making the projectile lose speed very quickly. "