Arizona received its fourth unmanned aircraft system (UAS) Tuesday in the form of a Predator-B drone. U.S. Customs and Border Patrol (CBP) officials say that the new military aircraft will assist three others based at the National Air Security Operations Center (NASOC) in Sierra Vista with counter-drug trafficking operations and other Homeland Security missions along the Southwest border.

According to CBP spokeswoman Gina Gray:

"Basing a fourth UAS in Sierra Vista will best posture CBP for rapid deployment throughout the southern tier of the United States and the Western Hemisphere."

Two more drones flying from Corpus Christi, Texas assist NASOC operations along the nearly 2,000 miles of border with Mexico.

"The missions from these two centers will allow CBP to deploy its unmanned aircraft from the eastern tip of California across the common Mexican land borders of Arizona, New Mexico, and Texas," CBP said in a statement.

The addition of the surveillance drone to the Arizona base brings the total number of CBP-operated drones to nine.  Six patrol from California to Louisiana in the south, and three cover the skies of Washington to Minnesota in the north.  The Department of Homeland Security says that along with border security, the Predators will be available, if needed, in case of disaster relief and humanitarian support.

Since the beginning of the U.S.-centered unmanned aircraft program in 2005, drones have helped in seizing about 46,600 pounds of illegal drugs and arresting almost 7,500 suspected criminals, CBP officials said.  The Obama administration announced last week that drone use along the Mexico border would be increasing as more than 1,000 National Guard troops sent to assist Border Patrol agents see the end of an 18-month deployment over the next two months. Reports from Washington suggest that Homeland Security drones will be flying as far as six miles into Mexico, tasked with preventing drug trafficking and border crossings by illegal immigrants.

But critics say the costs of the program outweigh the benefits.

The Government Accountability Office (GAO), using DHS and Department of Defense data, released a report in September which put the per flight hour costs of the Predator-B drone for fiscal year 2010 at approximately $3,234. “This is the total direct and indirect cost, including fuel, maintenance, support services, and labor," says the GAO report.

Homeland Security Department and GAO statistics reveal that drones along the U.S. borders have led to the detention of 238 drug smugglers and 4,865 undocumented immigrants over the past six years. The latter number represents less than 2% of the total of all illegal migrants caught along the southwest border in fiscal year 2011 alone.

The GAO report states that the government has spent almost a quarter-billion dollars for purchase and maintenance of domestic drones. This does not include the operation of the drones. Each UAS comes with about a $20 million price tag.

“Congress and the taxpayers ought to demand some kind of real cost-benefit analysis of drones,” said Tom Barry, trans-border project director at the Center for International Policy, reports the Washington Post. “My sense is that they would conclude these aircraft aren't worth the money.”

Other critics question the need for such extravagant and controversial technology to be used over domestic airspace.

The Predator-B, also known as the Guardian, is a variant of the Defense Department’s combat-ready Reaper UAS. It comes equipped with night vision/infrared cameras and other highly sophisticated sensors that can identify targets on the ground while cruising at an altitude of 50,000 feet. Depending on mission configuration and operational parameters, says the GAO report, the drones can stay aloft for up to 30 hours at a time. They can reach an airspeed of 252 miles per hour and carry a 3,000 pound payload.

According to a report in the Tucson Sentinel, retired Major General and assistant commissioner for CPB’s Office of Air and Marine Michael Kostelnick was quoted as saying that the drones being used along the U.S. borders are identical to those used in Pakistan and other war theaters, the only exception being that they do not carry weapons. Government officials say they do not intend to weaponize the domestic fleet.

The Department of Homeland Security is scheduled to receive 24 drones by fiscal year 2016. 11 of them will be used to patrol the Southwest border.