The Akula-class attack sub was a Russian submarine class in the 20th century. Akula class vessels used Shkval, an experimental torpedo developed by the Russians in the late 1970s, and improved upon since, which could reach a top speed of 100 meters per second, while an ordinary torpedo could travel at best 130 kilometers per hour; it operated on the principle of supercavitation, which reduced hydrodynamic drag by enclosing the torpedo within a self-generated bubble of water vapor and gas. Akula is Russian for shark.