FLORENCIA, Colombia (Reuters) - When spies spotted a guerrilla chief camped on a jungle riverbank one afternoon late last year, Colombia's army quickly turned to U.S. soldiers to help plan his capture.
Fresh from Afghanistan and Iraq and versed in the latest counter-insurgency tactics, the Americans said they analyzed everything from enemy troop strength to river levels and the moon cycle to forecast visibility.
Before dawn, Colombian soldiers were waist deep in water, moving toward the rebel, who they said was in charge of buying arms with cocaine profits in southern Colombia. The target soon lay dead in the mud. The U.S. Army asked that he not be named in order to shield American troops from reprisals.
The raid was one success in a multibillion-dollar U.S. effort to sharpen Colombia's campaign against the drug-funded Revolutionary Armed Forces of Colombia (FARC), which is fighting Latin America's longest-running insurgency.
But "Plan Colombia" is under tougher scrutiny as U.S. Democrats who now control Congress worry about the government's human rights record and ask why cocaine exports have not been more dramatically cut from the world's top producer.
They say too much aid goes into buying arms and fumigating coca crops in areas that would benefit more from establishing basic state services and a legal economy. Colombia says beating the rebels is the first step toward development.
"Before getting this assistance it would have taken us two days to evaluate the intelligence, plan and then launch the operation," said Andres Alfonso, chief of operations for the Colombian army's 6th Division, speaking of the recent mission.
His men had wanted to catch and question the rebel but they ended up killing him in the fight.
A decade ago it was no secret the army used right-wing paramilitary outlaws to fight the guerrillas. The paramilitaries massacred villagers, sometimes using hammers and machetes, in a terror campaign to control lucrative cocaine-producing land.
Complaints continue that Colombian soldiers are shooting peasants and passing the bodies off as rebels killed in battle, but gone are the blunt-edged military strikes that once killed everything that moved around suspected guerrilla targets.
Even critics of Plan Colombia say the U.S. advisers are making the army more professional and helping it push the FARC onto the defensive for the first time in decades.
"We are good fighters but not good planners, which is why this kind of aid is helpful," said Pablo Casas, an analyst at Bogota think tank Security & Democracy.
One of the Americans who planned the river mission and trained the soldiers who carried it out said the raid hurt the FARC's finances even though the army could not interrogate the guerrilla to unlock his money laundering secrets.
"We wanted to get him alive but by killing him the Colombians froze the guerrillas' ability to funnel drug proceeds into buying arms in this part of the country, at least for a while," said the soldier, who asked not to be named.
He is part of the nearly $3 million per-year Planning Assistance Training Team (PATT) program in which dozens of U.S. instructors are helping Colombia crack down on the drug trade.
All U.S. trainers are kept in safe areas away from combat.
Conservative President Alvaro Uribe is popular at home but his international standing has been hurt by a scandal linking some of his closest political allies to the paramilitaries, most of whom have demobilized under a government peace deal.
Colombian army units trained by U.S. forces are vetted to ensure they have never been accused of human rights abuses.
U.S. Democrats still worry that military aid is overemphasized.
"Security cannot be achieved through the use of force alone," Senator Patrick Leahy, the Vermont Democrat who chairs a key foreign aid committee, told Reuters.
The United States has spent $5.5 billion on Plan Colombia. But cocaine exports remain steady at about 600 tonnes per year, according to the United Nations, as farmers adapt to the aerial fumigation of coca crops by planting in better-hidden fields.
A very small part of Colombia's population lives in the Texas-sized part of the country southeast of the Andean mountain chain where the FARC still rules wide rural areas.
The rest lives in the industrial California-sized area to the northwest, where Uribe's security push has slashed urban crime rates and rejuvenated the economy.
One U.S. training team is based in Norte de Santander province on the Venezuelan border, where 11 soldiers died in combat last year compared with 29 in 2006, thanks in part to new first aid classes taught by the Americans.
As the FARC has been pushed into the jungles it uses more land mines to defend its positions. But Colombian soldiers had not been trained to stop bleeding or treat shock in the field.
"Compared to 2006 our deaths in combat were dramatically reduced," said Gen. Paulino Coronado, commander of the 30th Brigade on the northern border with Venezuela. "And it is our allies that have fundamentally strengthened us."
Reporting by Hugh Bronstein; Editing by Kieran Murray and Eddie Evans