LONDON – Military scientists are designing pilotless combat helicopters capable of carrying out air strikes with minimum input from their controllers on the ground.

The aircraft, known as unmanned combat-armed rotorcraft, are being built by two American defense contractors and are expected to be in use within eight years.

The scientists claim that the helicopters will be almost undetectable to radar, capable of distinguishing between hostile and friendly forces, and be able to locate and destroy hidden enemy positions by day or night in all weathers. They also believe that they will have the capacity to take autonomous decisions with little guidance from human controllers.

The limitations of existing technology mean that the military’s unmanned air drones, such as the American Predator and the British Phoenix – used for reconnaissance and missile attacks – are pre-programmed or remote controlled.

Although scientists admit that the concept of autonomous unmanned craft remains a “challenge,” they believe that it can be achieved within 10 years.

Researchers at Northrop Grumman, one of the two American defense contractors developing the aircraft, claim that the capacity for the machines to operate autonomously means they will be able to undertake a variety of missions alongside manned helicopters.

These will include identifying and engaging enemy targets or protecting manned aircraft by, for example, flying directly into the path of a ground-to-air missile.

Scientists believe that by the time the aircraft comes into service, advances in battlefield recognition equipment will eliminate the threat of friendly fire incidents.

They say that the helicopters will be fitted with a wide variety of sensors that will allow them to identify concealed and camouflaged targets and to distinguish between combatants and noncombatants.

American military chiefs are under stood to be developing a range of tactics for the aircraft, such as deploying them in mass formations to act as a vanguard or screening force for advancing troops. The fact that the aircraft are pilotless and able to fly at high and low altitudes means that they will be able to venture into combat zones that are regarded as too dangerous for manned craft.

The relatively low cost of the aircraft, at about $9 million each, will allow them to be more expendable than manned attack helicopters, such as the Apache. This is in service with the British and American militaries and costs about $18 million each.

Don Woodbury, the unmanned rotorcraft program manager with America’s Defense Advanced Research Projects Agency, said that the unmanned aircraft could be in service with the American army by 2012.

He said: “The commander [of the manned helicopter] will tell the unmanned rotor craft to fly into enemy territory, do a recce, to not fire unless fired on, report back at a specific time and stay within a certain air space. The unmanned craft will find and identify a target, pass the information back to the human, replan the mission, get a decision from the human and execute [the attack].”

He added that although the commander was in charge, he did not have to approve every action the unmanned craft made. “The commander will only have a certain amount of time to review and approve the plan or it will be implicitly approved by the unmanned helicopter,” he said.

Unmanned aircraft have been used with growing success and regularity by British and American forces in Afghanistan and Iraq. They were first designed for reconnaissance purposes in the mid-1980s and equipped with a single camera, later a video camera, which would return images of the battlefield.

The first use of them as attack aircraft was in November 2002, when a CIA-controlled Predator used Hellfire missiles to kill six suspected Al Qaeda members in Yemen.