"In the 1960's the Soviet Union had relatively slow, bumbling torpedoes that left its submarines at a serious disadvantage. Rather than push conventional torpedo technology a bit further, the Soviets decided to try to leapfrog the Americans with a radical solution.

The problem holding back ordinary torpedoes was drag. Any object no matter how streamlined, suffers resistance as it moves through a fluid. One source of drag is skin friction, the force required to shear the thin layer of fluid lying against the moving body's surface. As the power needed to overcome drag is proportional to the cube of an object's speed, each incremental improvement in propulsion technology produced only a meagre increase in speed.

In the early 1960's, Mikail Merkulov at the Hydrodynamics Institute in Keiv realised that the solution lay in a phenomenon called cavitation. It was a daring idea because naval architects usually see cavitation as a menace, rather than something that works to their advantage.

Supercavitation is a different matter. Under certain conditions, a single bubble or supercavity can be formed, enveloping the object almost completely. Newton alluded to the basic principles in his Principia Mathematica of 1687, but supercavitation is hard to achieve.

It was only in the early 1990's that the Russians were in a position to produce a proper working torpedo. Called Shkval, meaning Squall, it is said to be capable of speeds as high as 500 kilometres an hour.

The Russians had built themselves a formidable weapon. Shkval leaves enemy torpedoes standing, and can knock out an opposing submarine before it has time to react. It could even be used defensively to intercept enemy torpedoes."