And experts eyeing Jupiter’s moons say our world may not be the only one with an ocean to explore.

Several nations, including India, are researching supercavitation. But this technological horse race comes straight out of the Cold War and the former superpower rivals still dominate the field. Nerves are on edge. Kam Ng, a leading specialist on supercavitation at the Office of Naval Research agreed to discuss the fundamentals of the technology, but not how it might be tactically applied. "Undersea warfare tactic are a sensitive area. All I can say is: One can use supercavitation technology to produce high-speed undersea weaponry. The U.S. needs to defend such a weapon system," Kam wrote SPACE.com in an e-mail.

Scientists at the Naval Undersea Warfare Center in Newport, Rhode Island demonstrated in 1997 a fully submerged launch of a supercavitating projectile (with air injected in its nose) with a muzzle velocity of 5,082 feet (1,549 meters) per second, making it the first underwater weapon to break the sound barrier. More recently the U.S. unveiled supercavitating bullets. That program was inspired by the menace posed by harbor mines during the Gulf War. The slow and dangerous job of disarming mines often falls to divers because bullets lose momentum and direction after traveling a few feet through water, which is thousands of times denser than air. But supercavitating bullets fired from planes or helicopters could pierce and detonate mines from a safe distance.

The Russians, who during the Soviet era took an early lead in supercavitation in the 1960s thanks to Ukrainian experiments, remain extremely covetous of their advances in the field. Ask Edmond Pope, an American businessman and retired Navy captain imprisoned in Russia last year amid that government’s accusations that he spied on its supercavitation program. Rumors linger that Russia hesitated over seeking foreign aid in the aftermath of the Kursk submarine disaster because it carried experimental supercavitating missiles. But the Russians are selling one of their inventions – the Shkval-E (Squall) High-Speed Underwater Rocket.  According to their military sales brochure, the missile can top 200 miles (320 kilometers) per hour. But, that model Shkval is a "straight shooter," notes Kam, meaning that it can’t maneuver or home in on a target.

That brings up the point of steering – even without a bogey on your tail, the ocean is crowded place to go rocketing around compared to the relatively empty atmosphere. While Kam says collisions with fish won’t pose the kind of threat to a supercavitating vessel that flocking birds pose to jets today, few admirals would commit their best and brightest officers to a sub that moved only in straight lines. But turning is tricky. "[If] the bubble is distorted and hence air layer coverage is destroyed, the body becomes ‘wetted’ -- or there is no air layer to provide the low drag," Kam wrote. The answer is to rapidly adjust the orientation of the cavitator disk or cone at the craft’s nozzle and control ventilation to make sure surfaces under pressure are getting coverage. This is where mechanical engineering may need a helping hand from digital magic: using high-tech sensors and controls to maintain that air bubble through sharp turns, acceleration and deceleration, constantly changing pressures, altered body geometry (read: hull damage), vibration, contact with foreign matter and a host of other unpredictable variables.

The way it looks now, an experimental ramjet thruster engine called a vortex combustor will probably power a supersonic sub, according to Kam. Propellers would be useless because they wouldn’t be touching water. This engine reacts powdered aluminum with water in a contained whirlpool to produce heat that powers the ramjet turbine. "It has 2.5 to 3 times the specific impulse of solid rocket propellants," Kam notes.

Supercavitating missiles could also surprisingly revolutionize the more peaceful art of ocean farming. A supercavitating torpedo with a mooring line fired down from the water’s surface could maintain the force needed to slam an anchor deep into the sea floor, whereas such a remote system in deep seas using existing technology would slow and then simply clunk onto the sediment below. A report by Stanley Associates Inc. and Designers and Planners USA proposed using the technology to moor open ocean platforms for aquaculture instead of using divers or extensive underwater operations as with traditional drag embedment anchors.

But there’s one possible use of supercavitation that’s so wild it’s barely on the radar screen -- exploration of Jupiter’s moon, Europa. Magnetic and surface features indicate that this unique water world may contain under ice an ocean vaster than all the seas of Earth combined.

Despite Europa’s distance from the Sun (five times farther out than Earth) it may not be frozen solid. The conflicting gravitational tugs of nearby moons and Jupiter may be tidally flexing Europa’s metallic core much as a paper clip grows hot from repeated bending back and forth. And new data has opened the possibility that the Moon is volcanic like its ever-erupting neighbor Io. If so, a cross section of Europa would be a bizarre sight: fiery plumes spewing up into a giant sphere of water all encased within a seemingly placid shell of salty ice miles thick. And water, plus energy, plus nutrients kicked up by volcanoes and vents could equal life.

Scientists and engineers committed to charting this potential bestiary value swiftness as much as any tactician. "Speed equals potential to see more places, both areally and at depth, therefore leading to more data and more complete exploration," wrote Ronald Greeley, a planetary scientist at Arizona State University and a top Europa specialist.

As it is, NASA plans to land a probe on Europa’s surface, melt down through the ice to the expected ocean below, and simply dangle there from a tether to get a sense of the waters. But with a free, supersonic craft to explore that ocean "we’d gain access to a greater volume of the sphere, which sounds like a great idea," but one that’s "way beyond the speculative curve," remarked Lloyd French, a Jet Propulsion Laboratory engineer tackling the Europa mission. The advantage of a supercavitating probe would be that it could travel to points of interest (heat signatures, promising strata of current) rather than remaining stationary or mapping that huge sphere in its entirety, without discrimination, French said. The probe could also moor with a supercavitating torpedo at a position ideal for comprehensive, long-duration studies.

But the fuel demands of such a program are well beyond NASA’s current capacities, Lloyd and a colleague Wayne Zimmerman said. And if a probe were free to explore at high speeds, with less drag inefficiency (getting more territory covered before energy reserves run out) it would still have to find a way to communicate data back to the surface through ice, points out French, task manager for NASA’s Active Thermal Probe (Cryobot) Development Project, which is part of the Integrated Cryobot Experimental (ICE) probe for applications to Europa, Mars, Earth, comets and other icy environments. He advocates stringing radio relays through the ice as it re-freezes behind the lowered probe (the "bread crumb" method) but then any free-floating vessel would have to find its way back to its communications base. French notes another strategy might be to use the ice itself as an acoustic medium. That could provide the greater flexibility needed by a craft calling to the surface as it darts thousands of miles through a dark sea lit only be the fires at its core. And so another weird element could be added to the strange world of Europa: mechanical whale song.