In 1995 it was revealed that Russia had developed an exceptionally high-speed unguided underwater missile which has no equivalent in the West. Code-named the Shkval (Squall), the new weapon travels at a velocity that would give a targeted vessel very little chance to perform evasive action. The missile has been characterized as a "revenge" weapon, which would be fired along the bearing of an incoming enemy torpedo. The Shkval may be considered a follow-on to the Russian BGT class of evasion torpedoes, which are fired in the direction of an incoming torpedo to try to force an attacking to evade (and hopefully snap the torpedo's guidance wires). The weapon was deployed in the early 1990s, and had been in service for years when the fact of its existence was disclosed.
My understanding is that this rocket-propelled torpedo bleeds air into the water through thousands of tiny holes in the skin. This greatly reduces friction allowing the torpedo to travel considerably faster than anything the west currently has or is able to deal with.