FORT IRWIN, California -- Under cover of night, Airborne Rangers descend upon a simulated "hostile" territory as part of the armed forces' massive Millennium Challenge exercise at the huge, dusty, hot National Training Center at Fort Irwin in California's Mojave Desert. They descend with the kinds of weaponry and other lethal equipment you might expect. And as "Tech Live" reports tonight, some you might not.

Today they may also be packing electronic tricks of the trade, a part of warfare known as psychological operations, or psy-ops.

One technique is to set up a mobile radio or television station that can hijack existing broadcast signals. It gives the Army a way to transmit its carefully crafted message directly to the enemy -- right inside their own homes.

A mobile military television station can be set up in as little as four hours. And once it's in place, the Army can beam its signal to anyone within 16 kilometers. What's in those broadcasts? Some may call it propaganda, but the Army calls it "information distribution."

Blasting them with sounds

The Army can get a little more devious. Using recordings from simple audio or digital cassettes and massive speakers attached to vehicles, the Army can blast specific sounds to the enemy. These blasts can be heard as far as a mile away. Smaller speakers attached to soldiers can be worn inside the combat area.

Why? To mess with an enemy's mind. One recording is of a hysterical baby wailing. How would you like to hear that all night long?

But beyond simply annoying the enemy, psy-ops can serve a far more tactical purpose, such as tricking the enemy into believing that a small platoon is actually a much larger, deadly brigade.

"In the middle of the night you'll hear chopper sounds, and you'll start looking up, looking for the chopper, when actually it's my loudspeaker," Staff Sgt. William McLeroy said. "Or tank sounds. Hear them tanks start rolling around and the tanks aren't there. It's a facade."

The technology is used by the 315th Psychological Operations Company, which is based in Upland, California. The tapes are created on the Audiovisual Information Collection and Dissemination System. The large loudspeakers each have 1,000 watts of power. There can be nine attached to a vehicle. The smaller version, dubbed the ManPack, has about 250 watts of power and a range of up to 1,000 meters.

Officially, the technology is called a Force Multiplier. Unofficially, the Army says it gives a small dog a much bigger bark.

"We make them bigger so people will move back," McLeroy said.

Does it really work? During a demonstration, while a reporter was talking to McLeroy, a corporal began to play a tape of a chopper. Immediately, everyone around began to look to the sky to see where this chopper was and why it was flying so low. There was no chopper. The sound was incredibly realistic.

And in combat? "Believe me," McLeroy said, "it'll scare the pants off you."

This is the fourth story in our week-long look at military technology. Tomorrow's installment in "Tech Live's" Combat Week is about the latest high tech weapons on the water.