The Defense Advanced Research Project Agency has launched a technology demonstration project called the
Underwater Express to test applications of the concept of supercavitation on a super-fast submerged transport system
that ultimately could be used for special forces missions.
Once a concept is chosen to move forward, Phase 2
“will focus on stable vehicle dynamics by continuing to
examine supercavitation physics and cavity/vehicle interactions and developing the vehicle control approach.”
DARPA would not provide any of its experts to
explain the origins of the Underwater Express project
or the potential military use of what certainly would be
a very expensive means to transport a small load of
“high-value cargo” or personnel and equipment, as
Instead, DARPA spokeswoman Jan Walker said in a
written statement: “The military advantage of very-high-speed underwater craft has yet to be exploited to
its full potential because significant technological
breakthroughs are needed for operational viability of
“Also relevant are the current limitations for small
high-speed surface craft, which suffer performance
degradation in waves and are subject to visual exposure,
while underwater alternatives today are very slow.”
But Kamm Ng, who has directed the Office of Naval
Research’s (ONR’s) studies of supercavitation for nine
years, was more forthcoming.
“One of the potential uses for this vehicle is to
replace the special operation forces’ vessel Mark V,” he
said in an interview.
The Mark V is an 82-foot aluminum monohull surface craft that “bounces up and down in the water” and
at high speeds puts a lot of physical stress on its crew
and the SEALs. And, Ng added, it has “a much lower
speed … up to 40 knots.”
The Underwater Express could provide “up to two
times the speed to get the special forces to the target,” he
said. “So the potential cargo is really the special forces.”
ONR has explored supercavitation since 1997, picking up on research the Navy did in the 1960s to consider matching the Soviet’s Squall torpedo. The Navy
eventually dropped the project, deciding that quiet
performance was better than speed.
ONR’s more recent research also has been weapons-oriented and has helped in the development of systems
that use supercavitating projectiles to destroy shallow
Last year, DARPA asked ONR to share its supercavitation research to “jump start” the agency’s high-speed
underwater transport program.
But applying the supercavitation concept to something that could serve as a submerged transport poses
enormous challenges not confronted in weapons
development. For example, a quantum leap in power is
required to achieve 100 knots with an object 8 feet in
diameter, relative to that required for a high-speed torpedo, which has a diameter of 12 inches.
There are two ways to get the supercavitation “
bubble” around a submerged object. One is to get a blunt-nosed object going fast enough that the bow wave
pushes water away from the projectile’s body. The
other is to eject air or some other gas at the front of the
object to artificially create the bubble, which cuts the
drag and makes it easier to reach a high speed.
The Soviets used a rocket to propel the Squall. But
that would not work for a manned vehicle that must start
slowly, build up to speed and maintain it for possibly an
hour, then slow down again, said Franz Edson, director
of payload, sensors and strategic systems at Electric Boat.
The contractors would not discuss their respective
approaches to the propulsion challenge, for obvious
But Ng said water jets, powered by something like a
thermal engine, could provide enough energy to get
the larger vehicle up to 100 knots, once the bubble is
The greater challenge, the experts said, was detecting
obstacles and controlling a submerged vehicle going 100
knots and surrounded by an air pocket, when sonar or
other underwater sensing devices are useless.
The contractors noted that the initial phase of the
DARPA contract required them only to show they could