Holding the low ground: daunting challenges face those waging subterranean warfare.

• Author: Magnuson, Stew

To take a desktop trip into a clandestine tunnel, one only needs to visit the YouTube.com Web site and punch in the words "Gaza" and "tunnel."

In the clip, Israeli Defense Forces guide the viewers into a deep shaft that opens up into a passageway reinforced with wooden beams. It leads into Egyptian territory, and is one of many used to smuggle weapons, people and other contraband.

The IDF also had to deal with tunnels and deep bunkers in Southern Lebanon last summer when it squared off against Hezbollah fighters launching rockets into their territory. Reports said the underground complexes took years to construct.

But Israel isn't the only nation dealing with underground passageways or facilities.

In South America, the Colombian military found a network of tunnels used by Revolutionary Armed Forces of Colombia rebels, better known as FARC.

The Department of Homeland Security has unearthed several tunnels under the Mexican and Canadian borders. The largest, more than one mile long, was discovered last year near Otay Mesa, Calif.

Potential U.S. adversaries Iran and North Korea have reportedly built underground facilities to hide their alleged weapons programs. In the case of Iran, what kinds of weapons are being developed, and how extensive these facilities are, are subjects of much debate in the intelligence communities, but the advantages of keeping military assets out of the reach of air strikes or spy satellites, is unquestioned.

Coalition forces have had to deal with caves and tunnels in the mountains of Afghanistan as they chase al-Qaida and Taliban forces. If Osama bin Laden is hiding in Pakistan's tribal territories, as many believe, he's had five and a half years to dig himself a well-fortified and comfortable hole.

All this has not gone unnoticed by the U.S. defense community. Gen. John Abizaid, the former commander of U.S Central Command, indicated before a group of Washington-based reporters last fall that he has given the subject some thought. Overall, he was disappointed with the tools the military has to detect underground passageways.

"On a scale of one to 10, the technology is a four. We need more ability to see better underground," he said.

The public may associate clandestine tunnels with jailbreaks, but their use in warfare, both for offense and defense, is not new.

In 1864, Union troops dug a 500-foot tunnel under the Confederate line at Petersburg, Va. They planted 8,000 pounds of gunpowder beneath the fortifications and...