The Defense Advanced Research Projects Office (DARPA) has initiated an underwater express program to "demonstrate stable and controllable high‑speed underwater transport through supercavitation. The intent is to determine the feasibility for supercavitation technology to enable a new class of high‑speed underwater craft for future littoral missions that could involve the transport of high‑value cargo and/or small units of personnel. The program will   investigate and resolve critical technological issues associated with the physics of supercavitation and will culminate in a credible demonstration  a significant scale to prove that a supercavitating underwater craft is controllable at speeds up to 100 knots."

Such a 100-knot (115 miles-per-hour) undersea craft would be more than twice as the world's fastest submarine, the Soviet-built Project 661 (NATO code-name Papa). That submarine, completed in 1969, was armed with ten Amethyst anti-ship missiles (NATO designation SS-N-7) plus torpedoes. Twin reactors and twin shafts drove the Papa at 44.7 knots on trials--the fastest ever traveled by a manned underwater vehicle.  She subsequently went slightly faster in service.

A book published in 1988 offered some tantalizing glimpses into the future thinking of the Soviet Navy's leadership. The Navy: Its Role, Prospects for Development and Employment written by three naval officers with a foreword by Admiral Sergey G. Gorshkov, the long-time head of the Soviet Navy (who died the year that the book was published), predicted "in the near future" the Soviet Union would develop submarines with 50 to 60 knot speeds, and more than 100 knots in the long term.

The U.S. Seawolf (SSN 21) class is credited with being the fastest U.S. nuclear submarine. While the top speed of the two Seawolf attack submarines is classified, when they were under construction the Chief of Naval Operations said that they would have an underwater speed of 35 knots.

The current DARPA underwater express program is based on the concept of  supercavitation. This involves surrounding an object with a bubble of gas that allows it to travel at high speed by reducing contact with the surrounding water and hence reducing drag. The Soviet-developed VA-111 Shkvall (squall) torpedo is the best known use of this technology; that rocket-propelled torpedo has an underwater speed of about 200 knots.

In the United States the primary DARPA contracts for the "100-knot submarine" have been awarded to General Dynamics/Electric Boat, Northrop Grumman, New Systems Tech, and the University of Pennsylvania 's Applied Physics Laboratory.