The U.S. Border Patrol unveiled one of its weapons Tuesday in the war on drugs: Three wireless camera-equipped robots that let border agents remotely navigate the tunnels and storm drainage systems that smugglers use to sneak drugs, guns and people across the border.

The agency is using the devices to keep agents out of harm's way as many tunnels can be poorly built and possibly collapse and lack proper ventilation. The 12-pound robots also let agents navigate an underground labyrinth in a fraction of the time it would take an agent to explore the tunnel. And the devices can be used in tunnels and pipes where agents can't fit.

"If we find a tunnel, we like to send a robot into clear the tunnel and identify any threats, contraband, potential people with weapons, and let the agent know ahead of time if the tunnel is structurally sound," said Border Patrol Agent Kevin Hecht, an agency tunnel expert.

The Border Patrol held a demonstration of the devices Tuesday in the southern Arizona border city of Nogales, where dozens of crude tunnels have been discovered over the years. The tunnels discovered in Nogales have generally begun in Mexico and have tied into the Arizona city's storm drainage system.

Nearly 170 tunnels have been found nationwide since 1990, most along the Arizona and California border with Mexico.

The tunnel robots have been in use by Border Patrol for several years. But the agency recently paid $109,000 for the three new cameras with money from an asset forfeiture fund, which comes from the seizure of property in criminal cases, including drug cases involving cartel members, the Border Patrol said.

Two of the three robots will remain in southern Arizona, while the third is headed to southern California, where immigration authorities have used a tunnel robot for a number of years.

Tunnel construction ranges from extremely rudimentary, a small burrow dug by hand sometimes only large enough for a person to crawl through, to very sophisticated, including lights, supports to hold up the ceiling and ventilation. They can range from just a few feet stretching from one side of the border to the other, to up to a quarter mile long.

Some tunnels merely go from one side of the border to the other with the contraband being off loaded in a field or on public land, while others exit into warehouses or homes along the border.

Miners and other laborers hired by cartels use hoes, jackhammers, shovels and picks to gouge out soil and load the dirt into buckets that are brought back out of the tunnel's starting point in Mexico. Their tools are old-fashioned and can be bought at home improvement stores. Miners, for instance, must use compasses because GPS devices don't work underground.

Smugglers have dug dozens of crude tunnels in Nogales, Ariz., that begin in Mexico and tie into the Arizona city's storm drainage system.

For sophisticated tunnels, such as those found near San Diego, cartels will hire engineers and miners to build the tunnels. A cartel will have a financier or a cell that reports to the cartel bosses and runs the construction.

U.S. border officials estimate that the more sophisticated tunnels probably cost between $2 million to $3 million to build.

Smuggling groups use tunnels to move drugs, guns and people who want to sneak across the U.S. border, though traffickers are sometimes selective about what they will move through their tunnels.

Experts say sophisticated tunnels are used for mostly drug and gun smuggling, though people who don't want to risk traveling above ground will occasionally be sneaked through those tunnels.

Cocaine and methamphetamine are brought in through the tunnels, but marijuana — which is big and bulky and therefore difficult to move — is the most prevalent drug transported through the tunnels.

Authorities found a 600-yard tunnel in Southern California during November 2011 that resulted in seizures of 32 tons of marijuana on both sides of the border, with 26 tons found on the U.S. side, accounting for one of the largest marijuana busts in U.S. history. That tunnel was equipped with electric railcars, lighting and ventilation while wooden planks lined the floor.

Immigrant smugglers use "gopher hole" tunnels made up of huge PVC pipes that are buried underground and span the border, providing enough space through which a person can barely squeeze.

The storm-drain tunnels in places like Nogales are used for both immigrant and drug smuggling.

The majority of tunnels are found by human intelligence, either by Mexican or U.S. authorities patrolling the border and noticing the ground has been disturbed, or through informants who tip authorities to their presence.

So-called tunnel robots have been in use by Border Patrol for several years. They can safely navigate through corrugated pipes, tunnels, and drainage systems while an agent controls the device from the surface, seeing what the robot sees on a handheld screen. The robots are used, in part, as a safety measure to keep agents out of harm's way as many tunnels can be poorly built and possibly collapse and lack proper ventilation.

They also can navigate an underground labyrinth in a fraction of the time it would take an agent to explore the tunnel. Some of the newer robots, which weigh about 12 pounds and can navigate through passageways that are only several feet wide, are being deployed this year across southern Arizona and California.

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