The US Air Force has secretly developed a new stealth drone for long-range reconnaissance missions that could be operational by 2015, according to a report.

The unmanned drone, dubbed RQ-180, is currently in the testing phase at the top secret Groom Lake air base in Nevada — the infamous “Area 51” where the Air Force tested the U2 spy planes in the late 1950s, Aviation Week says.

The Air Force refused to comment on the report.

The new aircraft was reportedly built by Northrop Grumann, the company behind the Global Hawk and the X-47B drones, which landed on air craft carriers for the first time this summer.

The US company may have obtained in 2008 a secret contract on the order of $US2 billion ($A2.2 billion) to develop the latest drone, according to Aviation Week.

An artistic rendering of the RQ-180 on the cover of the magazine shows a craft with striking resemblance to the X-47B, in particular in lack of rear stabiliser and its so-called “batwing” shape.

It was developed for intelligence, surveillance and reconnaissance (ISR) missions, but “could also be capable of electronic attack missions,” the magazine said.

“It is similar in size and endurance to the Global Hawk”, which can fly for 24 hours up to 2000km from its base.

A first generation of unmanned aircraft, the non-stealthy Reapers and Global Hawks, were used in Afghanistan and Iraq, but they were deemed too vulnerable in enemy territory equipped with powerful anti-aircraft defences.

Now the Air Force is slowly turning to stealth drones, better at passing safely over unfriendly territory.