The idea, he said, was for the balloons to come down inside a supply or ammunition depot and explode. "It wasn't terribly effective," he said during a recent interview.

The Japanese tried a similar ploy late in World War II. They launched balloon bombs laden with incendiary and other explosives. The theory was high-altitude winds would carry the balloons over the United States, where the bombs would start forest fires and cause panic and mayhem. The Japanese weren't able to gauge their success and so called it a flop and quit after about a month.

The United States also tried a type of UAV during World War II called Operation Aphrodite. "There were some rudimentary attempts to use manned aircraft in an unmanned role. The limitation there was, we didn't have the technology to launch these systems on their own and control them" Weatherington said.

Allied forces used the modified manned aircraft basically as cruise missiles. The idea was a pilot would take off, get the plane to altitude, ensure it was stable and then pass control to another aircraft through a radio link before bailing out.

It was on one such top-secret Operation Aphrodite mission in 1944 that President John Kennedy's older brother, Navy Lt. Joseph P. Kennedy Jr., died when his bomber mysteriously exploded after takeoff.

During the Vietnam War, technology started to make UAVs more effective. Weatherington said they were used fairly extensively and were called drones.

Large numbers of modified Firebee drones overflew North Vietnam. The aircraft, about the size of today's Predator UAV, launched first for simple day reconnaissance missions at varying altitude levels. "They had conventional cameras in them," Weatherington said. "Later on, they were used for other missions such as night photo, comint and elint, leaflet dropping and surface-to-air missile (SAM) radar detection, location and identification."

One of these Firebees hangs in the Air Force Museum at Wright-Patterson Air Force Base, Ohio, amassing over 65 individual missions. As a whole, Firebees flew over 3,400 sorties during the Vietnam War.

Several of the UAVs we know today owe much to Israel, which develops UAVs aggressively. The U.S. Hunter and Pioneer UAVs are direct derivatives of Israeli systems, Weatherington said.

The Navy and Marine Corps operate the Pioneer UAV system has been in operation since 1985. Once during Desert Storm, Iraqi troops actually surrendered to a Pioneer.

At the time, the battleship USS Missouri used its Pioneer to spot for its 16-inch main guns and devastate the defenses of Faylaka Island, which is off the Kuwaiti coast near Kuwait City.

Shortly after, while still over the horizon and invisible to the defenders, the USS Wisconsin deliberately flew its Pioneer low over Faylaka Island. When the Iraqi defenders heard the sound of the UAV's two-cycle engine, they knew they were targeted for more naval shelling. The Iraqis signaled surrender by waving handkerchiefs, undershirts and bed sheets.

Following the Gulf War, military officials recognized the worth of the unmanned systems. The Predator started life as an Advanced Concept Technology Demonstration project. The program hurried the development of the Predator along, and it demonstrated its worth in the skies over the Balkans.

The Predator operates between 15,000 and 25,000 feet. It carries three sensor systems: a color video camera and synthetic-aperture radar.

The Air Force has also placed Hellfire missiles aboard the Predator. In the near future, the UAV might aim a laser at a target and attack it. The combat Predator can also mark targets with its laser for other aircraft or read targets marked by other sources.

Predator is not an all-weather system, however. As an result of lessons-learned in the Balkans, Predator employs a simple anti-icing system allows it to exit the icing condition but will not allow it to conduct continuous operations in the condition. The new Predator B has a number of characteristics that will better allow it to deal with a wider range of environmental events including icing conditions.

The Global Hawk is a jet-powered UAV taking to the skies over Afghanistan. Still under development, it is at the same stage the Predator was when it first flew over Bosnia. The Global Hawk operates around 60,000 feet, and its suite of sensors is akin to what the U-2 reconnaissance plane carries.

Global Hawk does not carry a very sophisticated signal intelligence system, Weatherington said. But, tests show the Global Hawk has great potential in this area and the Air Force continues to develop its full capability.

Persistence is a unique capability for UAVs, Weatherington said. The Predator can stay in the air for up to 40 hours. The Global Hawk -- at ranges measured in thousands of miles -- can loiter in an area for more than 24 hours.

So what's up for the future in UAVs? The Air Force and Navy are designing and testing combat UAVs. The Army is developing a tactical UAV called Shadow 200. This will give leaders "over-the-hill" surveillance capabilities. The Marine Corps has Dragon Eye, a small, hand launched UAV that can give small-unit leaders a picture of the battleground.

Some UAVs under development will be "as small as your hand," Weatherington said. "In the future it may be that a small UAV could fly into the window of a building, land at some innocuous location and observe activities."

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