The sub utilizes the phenomenon known as supercavitation. Supercavitation is the process wherein an object moves so fast through the water that it creates a gas bubble around itself, nearly eliminating drag. Unencumbered by the high drag of water, the object is free to speed along at much higher speeds than otherwise possible. Supercavitation has been known since the end of World War Two, and the Soviets succeeded in creating a torpedo that utilizes supercavitation for high-speed travel, but so far no one has succeeded in scaling the effect up to the size of a whole submarine.
http://www.popsci.com/military-aviation-amp-space/article/2009-07/darpa-readies-ultra-fast-mini-sub
Current supercavitating torpedoes (like those possessed by Russia and Iran) inject exhaust gas at the nose to help form and stabilize the gas bubbles they travel in. Such a mechanism on a 100 foot sub would be another thing entirely, and I am left to wonder where that gas would come from if the speeds were to be sustained... water vapor? would the friction of the nose be enough to sustain the gas bubble reliably? maybe water vaporized by on-board heat?
Interesting.
With such speeds a vessel could even make scary jumps high above the surface. That would open a whole new dimension in sub-sailing.
Submarines survive by being a quiet hole in the water, not by announcing "I'm right here... shoot me...shoot me!!!!"
Darwin friend!
american nuclear subs have been "schooled" of late in war games by quieter diesel-electric subs from foreign nations.
if a supercavitating sub can travel this fast, a supercavitating torpedo is going to be able to go faster and be launched from a super quiet and relatively cheap electric boat.
whizbang for sure, but militarily useless.