Two Border Patrol agents walked by a patch of brush on a remote ranch and saw nothing. But 19,000 feet overhead in the night sky, a Predator unmanned aircraft kept its heat-sensing eye on the spot.
In an operations center about 80 miles away, all eyes were on a suspicious dark cluster on a video screen. Moments later, the drone operators triggered the craft's infrared beam and pointed the agents directly to the undergrowth where two silent figures were hiding.
Last week's mission was just another night out for a Predator program that is playing a larger role in the nation's border security as the U.S. Customs and Border Protection adds to its force of unmanned aircraft. The agency received its second Predator B aircraft in Texas last month and will add its sixth overall on the Southwest border when another is based in Arizona by the end of the year.
The aircraft are credited with apprehending more than 7,500 people since they were deployed six years ago. They bring the latest in military technology to one of the oldest cat-and-mouse pursuits in the country. But on the border, even sophisticated devices struggle with the weather and conditions _ just as humans do.
"I'm trying to mark. I'm looking for a hole in the clouds," said an exasperated operator as he lost his video image of a "hotspot" in a stand of trees. Cloud cover, along with crosswinds and rain, are the drones' enemies.
The aircraft can remain airborne for 30 hours though missions typically run eight or nine hours with the ground crews rotating in the control trailers. Smugglers of humans, drugs and guns are the chief prey.
The Predators, which were being used in the wars in Iraq and Afghanistan, were introduced on the border in 2005, the year before Mexican President Felipe Calderon declared war on his country's drug gangs and violence along the border exploded. Since then, the aircraft have logged more than 10,000 flight hours and aided in intercepting 46,600 pounds of illegal drugs.
"It's like any other law enforcement platform," said Lothar Eckardt, director of the Office of Air and Marine's Predator operation housed at Naval Air Station Corpus Christi. "No different than a helicopter."
A Predator system _ the plane, sensors, control consoles and antennas _ costs $18.5 million. The craft's 66-foot wingspan stretches out from a relatively small body supported by spindly landing gear, making them appear almost insect-like. A single propeller powers them from behind, allowing for relatively quiet flights.
Inside the ground control trailer, a pilot and sensor operator sit side by side at consoles that include four screens each, a joystick, keyboard, several levers and rudder pedals. The pilot does the flying. The sensor operator works the infrared equipment and other technology under the aircraft's nose.
Some question whether the remotely-piloted aircrafts' impact justifies the price.
"The big knock on the UAS (unmanned aircraft systems) program ... is that it's so expensive," said T.J. Bonner, former president of the National Border Patrol Council, the agents' union. He said the money would be better spent on more boots on the ground and manned aircraft.
The Predator's touchiest missions are those that take it across the border into Mexico. A 2008 U.S. diplomatic cable posted by Wikileaks described a meeting between then Homeland Security Secretary Michael Chertoff and several members of Mexico's national security cabinet in which Mexican officials appeared to enthusiastically endorse the idea of surveillance flights. But publicly Mexican officials have been loath to speak about anything that could be perceived as impinging on the nation's sovereignty. In March, Mexican officials defended allowing U.S. surveillance flights and said a Mexican official was always present in the control room.
The Predator program now has one continuous patrolling zone from the Texas-Louisiana line, down the Gulf coast and up the border to El Centro, Calif.
U.S. Rep. Henry Cuellar, D-Laredo, who pushed to add the second unmanned aircraft in Texas and eventually hopes to have six based here, called them an "extremely important" part of the border enforcement mix of agents and technology.
"At that height out there, they can cover so much territory," he said.
Arizona will add its fourth Predator in Sierra Vista to help patrol from California to New Mexico and into West Texas. Eventually, one of the Texas aircraft will receive specialized maritime radar and concentrate on searching for smugglers in the Gulf of Mexico and western Caribbean.
For now, the Predator's greatest focus is along the US-Mexico border, where the drug war has increased concerns about spillover violence. They are especially valuable in night operations.
On that mission in the predawn hours Tuesday, the Predator guided agents tracking a group of six to eight illegal immigrants through thick clusters of oak trees and high grass an hour north of the Rio Grande. Seen through the agents' night-vision goggles the Predator cast a pillar of green light that illuminated two men lying in the undergrowth.
"It's awesome," Border Patrol agent Daniel Hernandez said. "It's a great asset to have here; something that made my job a little more efficient."