In Las Vegas a cowardly military assassin in an air conditioned trailer pulls the trigger. In Iraq a Predator fires its missile

An RAF unit based in the Nevada desert is conducting highly secret operations against Iraqi insurgents and Afghan guerrillas using unmanned, powerfully armed American Predator aircraft.

Opening 1115 Flight's doors to a news organisation for the first time, the unit commander, Sqn Ldr Andy Bird, told The Daily Telegraph that British crews had "engaged targets" six times and had inflicted casualties.

Many of the operational details are classified but RAF officers showed grainy video footage from one operation in which a Hellfire missile is seen striking a building used by an Iraqi sniper lying in wait for targets among coalition forces. The gunman was killed.

Another video showed the final moments of an Iraqi who was trying to set up a roadside bomb.

The 700 Predators, which are the size of a light aircraft, are based at airfields in faraway war zones but are piloted using satellite links from cabins at Nellis Air Force Base, on the outskirts of Las Vegas.

The aircraft, coated in bullet-proof kevlar material and nearly invisible to radar, has rapidly become one of the most valued weapons in modern warfare, giving commanders the ability to spy on an unsuspecting enemy and launch attacks on him.

It is viewed by admirers as a pin-up in the war on terrorism and has been used innumerable times by the American military and the CIA for intelligence gathering and to strike high-value targets.

Operators say the aircraft's cameras are powerful enough to determine whether a man on the ground is armed.

There have been well-publicised missed opportunities too. The Taliban leader Mullah Omar was caught in a Predator's sights but escaped when permission to fire was delayed.

Osama bin Laden is believed to have been sighted by a Predator camera in 2000 but the craft were not armed until February 2001. Other strikes have caused multiple civilian casualties, even if they hit their targets.

The American decision to share one of its most treasured and secret military assets is an extraordinary testament to the intimate and largely unseen special relationship with the British Armed Forces.

About one in seven military Predator flights is now flown by members of the 45-man RAF-dominated unit, while British servicemen hold many of the key roles in the two joint Predator squadrons and are lavishly praised by American commanders.

One commander said: "From day one, the British have sent their best - and it has shown. They perform at or above the level of everyone else."

At first sight, there is little to indicate that the Nellis base is involved in the gritty reality of live operations over the battlefields of Asia and the Middle East.

It is located in a sprawling complex in the unremarkable suburbs of America's capital of fantasy. Security is unobtrusive to the point of near-invisibility. Bland low-rise buildings and their vivid green lawns suggest a country club rather than combat.

Sqn Leader Bird said the strange surroundings made extreme concentration a key requirement when flying Predators. While the Predator crews are invulnerable, the ground troops they work with are not.

"You have to work very, very hard to keep that focus and remember that for the guys on the ground mistakes can cost lives."

Sitting side by side in dark, air-conditioned cabins, the pilot and sensor operator have to interpret activity in terrain as varied as the deserts and towns of Iraq and the mountains of Afghanistan.

Surrounded by technological wizardry that includes flight controls, maps and computer screens, it would be easy to drift.

Sgt Mac Mackenzie, 41, an Army sensor operator who has served in Northern Ireland and Iraq, said: "It is not always appreciated that this is what we have to do. You are just staring at the screen. Then suddenly it can go live, you're involved in an engagement, a target appears and everything is turned on its head."

Minutes later, a 12-hour shift may end and the men find themselves stepping into the desert, a one-second transition from Iraq to Nevada.

The British crews acknowledge that there is an air of unreality about their work, "staring at a screen for hours, watching what is happening then walking out into the heat" before driving home to their families in the suburbs of Vegas. Time off is generally spent among the bizarre architecture of the city centre, where fake pyramids, castles and the "Eiffel Tower" vie in multi-coloured capitalist anarchy for the attention of armies of gamblers.

British crews have been based at Nellis for two years, in which time some of the missile strikes have attracted headlines. But more than 90 per cent of their work is the collection of intelligence.

They spend "a significant amount" of time on special forces operations but have also tracked down guerrilla commanders, scouted ahead of convoys, sighted ambushes and rescued coalition troops who have become separated from their units.

The Predator is little more than a snowmobile engine strapped to a glider. It barely accelerates over 100mph but it flies at up to 25,000ft.

It carries a cargo of cameras, heat sensors and missiles that provide "a God's-eye view" of the battlefield, day and night. It also has extraordinary endurance, being able to stay aloft for 20 hours or more.

For many coalition ground commanders, that capability is so important that critical military operations are sometimes postponed until a Predator becomes available.

The joint manning of Predator has caused some tensions. British commanders in Iraq have complained that they are given too little of the aircraft's time despite the British presence at Nellis and the RAF, the Army and the Royal Navy men have had to make adjustments.

While personnel apply British rules of engagement and wear British uniforms, they fly American aircraft, use American communications equipment and wear American squadron flashes.

Chief Technician Gary Smith said: "We have been here so long that now we are training the Americans.

"Sometimes when you give their lads an order, you can see them stopping and wondering, 'Do I have to do this?'"