Friend or Foe? A Digital Dog Tag Answers

AS violence boils in Iraq, American troops and allied forces are in danger - not just from local insurgents and militias, but from their own side as well.

Despite precautions taken by the G.I.'s, despite the growing accuracy of bombs and other weapon systems, despite an ever clearer picture of the combat zone from surveillance drones and spy satellites, soldiers continue to be killed by fire from their own comrades.

But new technologies being tested by the American-led forces have the potential to prevent many of these accidental attacks. Using a combination of radio frequency transponders, laser sensors and microwave-like transmitters, the Defense Department hopes to give every allied soldier, tank and plane a unique identifier to distinguish friend from foe.

Traditionally, mistaken attacks - what the military calls friendly fire - account for 15 percent or more of combat casualties, said Pete Glikerdas, who manages combat identification programs for the Army's Research, Development and Engineering Command. "Our goal is to bring the friendly fire problem down to less than 3 percent," Mr. Glikerdas said.

In Iraq, the majority of accidental casualties have been caused by air-to-ground attacks, said Lt. Col. Wayne Shanks of the Joint Forces Command. In April 2002, for example, an American F-16 pilot killed four Canadian soldiers and wounded eight when he dropped a 500-pound bomb on a group that was training near Kandahar, Afghanistan.

Radio frequency tags - transponders about the size of a bar of soap - may help prevent such assaults.

From the grainy images produced by a fighter plane's sensors, it is often hard to tell what side a truck or a tank or a band of soldiers is on. When hit by a plane's radar signal, though, the radio tags send a signal back with additional information that identifies the equipment or person.

The most sophisticated of the tags sample the radar's waveform, like a recording engineer sampling a melody. To this, the tags "add a harmony, or even a counter-melody, with its own unique structure," said Jay Saffold, president of the Research Network, based in Kennesaw, Ga., which is evaluating combat identification systems for the Army. The new signal is returned to the aircraft, which then processes it and extracts the information sent by the tag.

Such transponders have been around in one form or another for decades. Yet increasingly powerful computer processors have allowed the tags "to go from suitcase or backpack size down to cigarette pack size," said Lt. Col Bill McKean of the Joint Forces Command. And that in turn is making the devices inexpensive enough for the Pentagon to start thinking about widely distributing them among troops.

The transponders are one of a number of identification technologies that American, British and French forces will test during combined exercises along the East Coast in June.

Mistaken attacks became a major issue for the Pentagon after the first Persian Gulf war in 1991, when they caused 24 percent of the deaths of American soldiers.

But a comprehensive effort to reduce such accidents has been slow in coming. "I don't think we've made a lot of progress in the last 10 years," Brig. Gen. Robert W. Cone of the Army said at a briefing last October.

The American-led forces in Iraq today have tools for preventing such mistakes, but many of them are decidedly low-tech: reflective panels that show up in weapons systems' thermal sights, and hand-held strobe lights that are invisible to the naked eye but instantly recognizable to a soldier wearing night vision goggles.

More important, perhaps, are the new satellite-based systems for tracking allied forces. Every few minutes, vehicles outfitted with the Army's Blue Force Tracking system communicate their whereabouts to a central headquarters. There, a composite map of the battlefield is created, showing where all of the units equipped with such tracking systems are. That picture is then sent to the vehicles over an encrypted high-frequency satellite link.

Instead of the tracking system and other so-called passive approaches, which simply transmit units' whereabouts, Colonel McKean and others are working to develop "cooperative" identification programs like the radio frequency tags. These are systems that allow a shooter to, in effect, ask his target whether he is a friend or not and enable the target to reply instantly.

For tanks and armored vehicles, the military wants to use millimeter waves, a shorter cousin of microwaves, to make the queries. The Battlefield Targeting Identification Device system uses a shoebox-size transmitter to send such waves toward a target before the shooting starts. An encrypted reply can return from as far as four miles away in less than a second, Mr. Glikerdas said.

The system's 25-pound transmitters are too heavy for troops moving around a combat zone on their own two feet, however. So instead, the laser range finders on soldiers' rifles are being retooled to ask the question, "Friend or foe?" All soldiers would wear sensor tags that, when hit by a laser beam from a range finder, would generate a "friendly" signal transmitted by the soldier's radio.

This approach has shortcomings, Mr. Glikerdas admitted. Rain, fog and dust can disrupt laser beams. And not every soldier has a radio; those are usually saved for a squad's commander.

Ivan Oelrich, the director of the Federation of American Scientists' strategic security project, said he worried that the whole "cooperative" approach might be flawed.

"You run the risk of giving your own position away if you're sending out a signal," Mr. Oelrich said. "Even if your enemy can't figure out the code, he can at least figure out that you're querying him. And he can start shooting in your direction."

No technology, Colonel McKean acknowledged, will ever be able to flawlessly pick out friend from foe, much less civilian from combatant. But clearing away even some of a war's fog is worthwhile nonetheless, he said.

"Improving the capabilities is still worth the cost," he said, "because you're saving lives."