The US Defense Department has asked defense companies to develop a giant craft that could hover high in the stratosphere and be used to spot incoming enemy missiles and planes, it reported.

Pentagon and defense industry officials say technological advances, including highly efficient solar cells, make airships a potentially invaluable addition to the US arsenal.

"We are very excited about high-altitude airships," Sue Payton, the Pentagon's deputy undersecretary for advanced systems and concepts, said in a recent briefing with industry executives.

The airships would be far more complicated than any built before, and could be deployed within seven or eight years, according to a transcript of Payton's comments as reported in the newspaper.

The newspaper wrote that a helium-filled airship could be capable of floating for months at an altitude of some 70,000 feet (21,000 meters) carrying more than 4,000 pounds (1,800 kilograms) of unspecified payload.

SPACE.WIRE