Plan Colombia - the $3bn (£1.7bn) US effort to hit cocaine at its source - has become embroiled in the country's 40-year armed conflict. The BBC's Paul Kenyon travels with the Junglas, an elite anti-narcotics unit, as they comb the Colombian rainforest for "cocaine laboratories".
We were flying high over the Colombian jungle when the incoming fire began.
Our unit responded with machine guns. Two long bursts.
Then all we could hear was the thudding of the rotor blades.
The men defending a hidden cocaine laboratory had fled into the trees.
The team we were travelling with, called Junglas or jungle men, risk their lives regularly on missions like this.
They are funded and trained by the Americans and are part of the biggest US military effort outside the Middle East or Afghanistan. They represent the front line of Plan Colombia.
But, after five years of this type of operation, alongside an unprecedented spraying campaign against the coca crops, is Plan Colombia actually working?
Plan Colombia gives government forces money, weapons and training
We land near a series of tents, more like a shanty town than a "laboratory".
This ragtag village, with living quarters and kitchen, was producing around two metric tons (4,410lb) of cocaine a week before the Junglas arrived.
Two months of production here amounts to around £800m ($1,440m) worth in UK street prices; enough to buy Manchester United football club.
As we leave, the Junglas lay explosives.
Two huge thuds and the lab is in flames. But, as one Jungla points out, for every one they destroy, another one is built.
As Colombia supplies 90% of the world's cocaine, they are in the right place, but the market is no longer controlled by drug barons.
Instead two armed groups fight over land and cocaine laboratories: the Marxist guerrillas known as the Revolutionary Armed Forces of Colombia (Farc) and the right-wing paramilitaries.
They used to fight over ideological differences, funding themselves through cocaine, but these days the fighting is over the cocaine itself.
As a result, the challenge for Plan Colombia has grown more intense.
The United Nations and the Americans say the quantity of coca being grown has halved over the five years since Plan Colombia began.
"The figures that we are most confident of, are the figures on what we have destroyed in the fields and what we have seized with the Colombians," says US Ambassador William Wood.
"Those numbers are absolutely certain and we know that the amounts of drugs we have taken away from the bad guys and prevented from getting to market is going up dramatically."
But there are some well-placed officials in Colombia who disagree.
We are taken deep into a paramilitary-controlled area by the vice-governor of Narino province, Fabio Trujillo.
"No," he says. "I don't think the UN observations are correct, I think there is a lot more coca than that... in Narino I observe that the hectares of coca have continued to increase."
Mr Trujillo took us through fields he said the US satellites had been unable to locate because of the almost continuous cloud cover.
There we met a coca farmer, Elias Vivas.
He lives in a tiny two-room shack with his family of six.
Americans fight alongside Colombia's elite anti-narcotics units
He says this is the only crop he can grow that is guaranteed to sell, and that he can harvest four times a year.
His crop was sprayed nearly two years ago, but it did not stop him.
"It hit us economically," he says. "It just meant that I had insufficient food to give to my children."
That has long been seen as the problem with coca spraying. It is the small farmer who gets hit, not the people who own the laboratories.
But while the US and the UN say the plan is working, the street price of cocaine in the UK and the US is unmoved and in some places, falling.
The normal laws of economics suggest that means there is more of it around, although William Wood says there are too many variables to draw that conclusion.
Most damaging for the US has been two cases of corruption involving their own special services on duty in Colombia.
First, a group of soldiers was caught trying to smuggle around £1m ($1.8m) worth of cocaine out of the country and into Texas.
Then, two officers were trapped by Colombian police as they tried to sell ammunition in a deal with the paramilitaries.
Ambassador Wood says: "I am not going to speculate on these cases. They are enormously saddening. They are a denial of why we are here.
"They are a denial of the standards of several hundred American military people. They are a denial of our close co-operation with Colombia."
All sides appear to be in agreement over one worrying development though.
Despite the claim that coca growing has fallen dramatically inside Colombia, it appears the growers are simply being displaced over the borders to Peru and Bolivia - where figures for coca production are definitely on the rise.
The Cocaine Jungle was broadcast on Wednesday, 19 October, 2005 at 1900 BST on BBC Two.