Yet despite having the world's most advanced military, the United States has not been able to develop a foolproof system for distinguishing between friendly forces and enemies on the battlefield, experts say.

"We've never really licked that problem," said retired Marine Lt. Gen. Robert Johnston.

While he wouldn't speak directly about the incident that killed Spc. Alan McPeek, a Tucsonan, and Pvt. Matthew Zeimer, Johnston, who served as chief of staff for Gen. Norman Schwarzkopf during the first Persian Gulf War, said most friendly-fire incidents result from inexperienced troops losing situational awareness in battle.

Retired Lt. Col. Charles R. Shrader, who wrote a book on friendly fire in modern warfare, said what happened to McPeek and Zeimer is sadly typical of most similar incidents.

"In the heat of battle, (troops) just don't pay attention," he said.

Friendly-fire deaths captured the nation's attention in 2004 when Pat Tillman was killed in Afghanistan.

General inexperience on the part of Army Rangers led to the death of the former Arizona Cardinals football player, an investigation found.

Investigations showed that the Army knew within hours that Tillman was killed by members of his own unit, but didn't tell his family for more than a month. A full account of the incident wasn't released for more than two years.

In the aftermath of the Tillman fallout, the Army vowed to strengthen efforts to investigate friendly fire and try to be more open when similar incidents occurred.

But after the deaths of McPeek and Zeimer, family members initially were told that the two men were killed by enemy fire. It wasn't until a month later that they learned Army officials suspected friendly fire.

There were differing accounts of what occurred when McPeek and Zeimer were killed, which required investigators to find evidence of friendly fire, said Army Lt. Col. James Hutton, a spokesman for the Multi-

National Corps based in Iraq.

Statistics on friendly-fire casualties have proved elusive because of the nature of the incidents and the fact that past records weren't as detailed.

Shrader estimates in his book that roughly 2 percent of combat deaths are due to friendly fire.

The Marines have recorded six deaths as a result of friendly fire stemming from incidents in Iraq and Afghanistan.

Army figures on deaths weren't available by deadline, with the Navy and Air Force recording no such deaths.

There have been dozens of injuries as a result of friendly fire, military figures show.

While it would be easy to examine a friendly-fire incident and point to one mistake as the cause of a particular death, that's usually never the case, Shrader said.

"There's seldom just one thing that goes awry," he said.

Sound Off...What do you think? Join the discussion.

Copyright 2009 Arizona Daily Star. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

More Military Headlines

• ABCTE Offers the Passport to Teaching Program
• Clint Eastwood Used the GI Bill
• DoD Changes Policy on Selected Reserve GI Bill
• Earn Your Degree No Matter Where the Military Sends You
• Japan Considering THAAD Missile Defense