The fastest submarine in the US Navy can go only 25 to 30 knots. But the Electric Boat Corporation, the primary designer for US Navy submarines, is trying to design one that can reach up to 100 knots. It plans on testing a 1/4 scale model off the coast of Rhode Island next year:
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.