In 2000, when the United States expanded assistance to Colombia in its battle against the narcotics-financed insurgent group called FARC, the trainers were military, not D.E.A. But after the invasion of Afghanistan, the Bush administration assigned Mr. Braun, a veteran of the earlier effort, to design a new program.

Begun in 2005, the program has five squads, each with 10 agents. Many are military veterans, and the section is overseen by a former member of the Navy Seals, Richard Dobrich. The Pentagon has provided most of their training and equipment, and they routinely fly on military aircraft.

The deployments to Afghanistan have resulted in large seizures of drugs, and some tragedy: two of the three D.E.A. agents who died in a helicopter crash in October 2009 were with FAST. Last week, an agent was shot in the head when his squad came under fire while leaving a bazaar where they had just seized 3,000 kilograms, about 6,600 pounds, of poppy seeds and 50 kilograms, about 110 pounds, of opium. Airlifted to Germany in critical condition, he is expected to survive, an official said.

The commandos have also been deployed at least 15 times to Latin America. The D.E.A. said some of those missions involved only training, but officials declined to provide details. Still, glimpses of the program emerged in interviews with current and former American and foreign officials, briefing files, budget documents and several State Department cables released by WikiLeaks.

For example, an American team assisted Guatemalan forces in the March 2011 arrest of Juan Alberto Ortiz-López, whom the D.E.A. considered a top cocaine smuggler for the Sinaloa cartel, an official said. Videos of the raid show masked men in black tactical garb; it is unclear if any are Americans.

A diplomatic cable describes another mission in Guatemala. On July 21, 2009, seven American military helicopters carrying D.E.A. and Guatemalan security forces flew to the compound of a wealthy family, the Lorenzanas — four of whom were wanted in the United States on drug trafficking charges.

After a “small firefight” in which a bullet grazed a Lorenzana family member, agents found “large numbers of weapons and amounts of cash” but not the targets, who may have been tipped off, according to the cable. The Guatemalan news media documented the failure, portraying the joint operation as a “D.E.A. raid.”