Hanoi - "Stay close to the walls, and don't expose yourself," the American adviser told the Vietnamese officers as they advanced into a building, weapons drawn. The scene this week was reminiscent of a South Vietnamese Army training camp in the 1960s, but these Vietnamese officers were anti-narcotics police, and the adviser was an agent from the US Drug Enforcement Administration (DEA).
For a week and a half, a team of DEA agents and US military medics have shown 80 Vietnamese police, customs officials and border guards the American way to conduct a drug raid: planning, entry and arrest techniques, self-defence and emergency medical care.
Communist Vietnam now has close diplomatic and trade relations with the United States, its enemy during the Vietnam War, and the country's Ministry of Public Security seems happy to accept American help in fighting the narcotics trade.
"The drugs problem is an international problem," said Joe Boix, a square-jawed DEA firearms instructor from Phoenix, Arizona, who was leading the training. "It's all the same no matter where you go."
Vietnam is a waypoint on international narcotics-smuggling routes and has a serious heroin problem with the number of addicts particularly high in its north-west, where heroin is smuggled in from neighbouring Laos.
Inside Vietnam itself, opium poppies, once grown widely, were stamped out by the government in the 1990s, according to the UN, but Laos produces a small amount of opiates each year, and nearby Burma is the world's number two producer of heroin, after Afghanistan.
In recent years, Vietnamese drug users have branched out from using heroin to ecstasy and methamphetamine although authorities said none of these synthetic drugs were produced in Vietnam.
Authorities reported record drug busts, with the Cong An Nhan Dan, or People's Police, newspaper claiming police had seized 83 kilograms of heroin and 89,000 amphetamine pills so far this year.
In the past two months, six women have been arrested in Vietnamese airports smuggling heroin to or from Australia. In May, four Chinese men and an Indonesian were caught trying to cross into China with 9 tons of hashish hidden in a shipping container full of jeans.
"Our main thrust is to go after the international organizations," said Jeff Wanner, the DEA's liaison officer in Hanoi. "This training is to help [the Vietnamese] deal with their internal problem, but we want to go after the bigger organizations, international in scope."
The DEA office in Vietnam is not permitted to carry out hands-on operations, but Wanner said the office exchanges intelligence on drug activity with Vietnamese agencies.
The training in Hanoi was very hands-on. In classrooms belonging to a firefighting academy, DEA agents ran through physical arrest exercises with Vietnamese officers, forcing "suspects" to lie on their stomachs, handcuffing them, then moving them to a squatting position and pushing them to their feet.
Captain Luu Duoc Cuong, a border guard from the northern province of Cao Bang, said the techniques were similar to Vietnamese ones but with a few differences.
"In America, once the suspect has surrendered, if he begins to resist, to be difficult or doesn't listen, you can shoot him," Cuong said. "In Vietnam, if he's surrendered but doesn't listen, you still can't shoot."
In the parking lot, where a plywood mock-up of a house was constructed, Boix coached teams of Vietnamese agents in forcibly entering the house and then, one by one, clearing each room and arresting suspects.
"Slice the pie!" Boix called out, using a term that refers to the way a pair of agents, standing at the corners of a door, visually divide the room inside as they scan for targets.
Two agents drew their guns on a colleague role-playing a suspect, shouting in Vietnamese, while an interpreter translated for Boix's benefit: "Police! Hands up!"
A moment later, shots rang out. Paint pellets splattered on plywood walls.
Some minutes later, Boix reviewed the raid with his students.
"In the first incident, there were two misses in very close proximity," Boix said. "We must make every shot count, so no one is injured unnecessarily and we go home safe to our families."
"It's exciting for them to be able to actually pull the trigger and try to pretend like there are bad guys coming at them," Wanner said. "This is what we all trained for."