The agency sponsors research into numerous aspects of military operations, particularly technology, it says, "where risk and payoff are both very high and where success may provide dramatic advances for traditional military roles and missions."

The artificial black ice is one of its newest projects. DARPA recently called for proposals from scientists to develop a polymer-based material that acts like the sheer ice that forms on roads in cold temperatures, sending unwitting drivers spinning out of control.

But the polymer ice could be used against enemies in any climate, including hot, arid ones like Iraq and Afghanistan where US troops are currently fighting. The idea is to lay down the ice to cause adversaries to slip, while US troops would make use of a to-be-developed "reversal agent" -- something to be incorporated into their boots and tires -- that would allow them to gain traction on the "ice."

"Such a system will provide unprecedented situational control and sustained operational temp," DARPA says, "including the ability to shape the terrain by constraining adversaries to specific areas (and) degrade the ability of our adversaries to shoot and chase us."

Closer to development is a ray gun that DARPA unveiled last week, its so-called active denial system (ADS): a weapon that emits a beam of energy that will make the target feel a strong burning sensation on their skin, repelling them without causing genuine injury.

Mounted on a trailer, the ADS is a parabolic antenna-like unit that shoots out a focused electromagnetic radio-frequency beam of millimeter waves over 500 meters (yards), giving it a much greater range than many crowd-control devices like rubber bullets or water cannons.

When they hit their target, the beams penetrate the skin to about 1/64th of an inch, or 0.4 millimeters, causing a sensation that makes people think their clothes are on fire. This can be used to scare off a menacing mob without causing real injury, according to DARPA.

DARPA stresses that ADS is not a laser, nor does it use more dangerous microwave energy.

"We need discriminate, non-lethal weapons with longer ranges and universal effects. This is exactly what we get with ADS," said Colonel Kirk Hymes, the head of DARPA's Joint Non-Lethal Weapons Directorate.

It has taken DARPA 12 years to get ADS to this point, and it will be several more to get it on the battlefield.

Hymes says such weaponry is part of the equipment US soldiers need in the battlefields of the 21st century.

"Our warfighters have identified a need for additional non-lethal capabilities, because distinguishing between combatants and non-combatants on the modern battlefield can be very difficult," he said.

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