In recent years, members of the Shadow Wolves have mainly tracked smugglers along the US border with Mexico.
But the Taliban's resurgence in Afghanistan and the US military's failure to hunt down Osama bin Laden - still at large on his 50th birthday on Saturday - has prompted the Pentagon to requisition them.
US Defence Secretary Robert M.Gates said last month: "If I were Osama bin Laden, I'd keep looking over my shoulder."
The Pentagon has been alarmed at the ease with which Taliban and al-Qa'ida fighters have been slipping in and out of Afghanistan. Defence officials are convinced their movements can be curtailed by the Shadow Wolves.
The unit has earned international respect for its tracking skills in the Arizona desert. It was founded in the early 1970s to curb the flow of marijuana into the US from Mexico and has since tracked people-smugglers across hundreds of square kilometres of the Tohono O'odham tribal reservation, southwest of Tucson.
Harold Thompson, a Navajo Indian, and Gary Ortega, from the Tohono reservation, are experts at "cutting sign", the traditional Indian method of finding and following minute clues from a barren landscape. They can detect twigs snapped by passing humans or hair snagged on a branch and tell how long a sliver of food may have lain in the dirt.
Some military experts want the Shadow Wolves to help to track down bin Laden. Despite a $US25million bounty on his head and the use of billions of dollars worth of sophisticated equipment, US forces have so far failed to fulfil President George W. Bush's promise to capture bin Laden "dead or alive".
But a senior US official insisted last week that bin Laden's trail had "not gone stone cold". Vice-Admiral Mike McConnell, the new US director of national intelligence, told a Senate committee that bin Laden and his lieutenant, Ayman al-Zawahiri, were setting up new training camps in northwestern Pakistan.
The deployment of the Shadow Wolves came as Iraqi militants holding a German woman and her son threatened yesterday to kill their captives unless Germany started withdrawing its troops from Afghanistan within 10 days.
The 61-year-old woman made a tearful plea for help to German Chancellor Angela Merkel in a video posted by the abductors on an Islamist website.
"I'm asking you to help me," she said in German, sobbing. "We're Germans as well. These people want to kill my son before my eyes and then kill me. I don't want to die like this."
Hannelore Marianne Krause and her adult son were seized on February 6 by armed men who burst into their family home in Baghdad. One of the kidnappers read a statement in Arabic on behalf of a little-known group calling itself the brigade of the Arrows of Righteousness.
"We give the German Government 10 days from the date of this statement to announce and start the withdrawal of their troops from Afghanistan, otherwise ... they will not even see the bodies of these two agents," he said.
