The fully deployed system consists of four air vehicles, a ground control station and a Predator primary satellite link, and is operated by 55 people.

It was developed in the 1990s for use in what the US describes as "moderate-risk environments" - where enemy air defences remain a threat, or in areas which may have been contaminated by chemical or biological weapons.

With its bulbous nose, the aircraft has a wingspan of 48.7 ft (14.6m), weighs 950 lbs (430 kgs) empty and 2,250 lbs (1,020 kgs) when fully equipped for reconnaissance, surveillance or target-finding missions.

Each Predator is fitted with:

• colour nose camera - generally used by the operator for flight control
• daylight TV camera
• infra-red camera for poor light/night missions
• radar to scan through smoke, clouds or haze.

Cruising at up to 25,000 ft (7,500 m), the planes have a maximum speed of 140 mph (225 km/h) and a range of 454 miles.

Their relatively slow speed, however, makes them vulnerable to missiles and anti-aircraft gunfire.

Losses

Iraq says it has this year shot down two Predators over its airspace where the aircraft have seen extensive use.

In February this year the first armed Predator, fitted with a dummy anti-tank missile, was successfully tested in the US, suggesting that the planes may soon fulfil a more deadly role.