A launch crew prepares a Northrop Grumman X-47B Unmanned Combat Air System.

A launch crew prepares a Northrop Grumman X-47B Unmanned Combat Air System.

When an aircraft shaped like a bat was lowered gently by crane onto the deck of a US nuclear-powered aircraft carrier the other day, it marked the latest phase in a high-stakes gamble to help sustain America's military presence in the Asia-Pacific region in the face of increasing challenges from China.

The Chinese armed forces are developing anti-ship ballistic missiles and other weapons which are difficult to defend against to try to keep US carriers and their manned jet fighters several thousand kilometres from China's mainland in a crisis. In response, the US is seeking ways to keep its forces and military personnel safe from attack by operating at much longer ranges.

The arrival of the tailless and stealthy X-47B on the USS HarryS. Truman at the Norfolk naval base in Virginia on November 26 is the first time an unmanned combat jet plane has been on a carrier. The X-47B is an experimental strike and surveillance aircraft. It is designed to perform one of the most difficult feats in aviation - to land and take off safely from a carrier deck at sea, and to do so without a pilot.

The X-47B is computer-controlled and designed to take off, fly a pre-programmed mission, then return to base in response to mouse-clicks from its mission operator. The operator monitors the flight and can vary its computer-programmed instructions if necessary. But the operator does not actively ''fly'' it via remote control as with other unmanned drones now in operation.

For the next few weeks, the X-47B on the carrier will be given flight deck movement tests. Meanwhile, a second X-47B will practise touching down and taking off on a simulated carrier deck on land. It was launched by catapult for the first time on November 29.

The drone is due to make its first landing on a carrier next year, relying on pinpoint global positioning satellite co-ordinates and advanced avionics to touch down precisely in time to catch an arrester wire on deck, abort the approach if required, and take off again if the hook misses the wire.

If all goes well, aerial refuelling of the X-47B will start in 2014 and involve both unmanned and manned tankers. This would be a critical stage in development of the X-47B, which has been under way for the US Navy since 2007 and has already cost over $US800 million ($760 million).

The X-47B is similar in shape to the much larger US B-2 long-range manned stealth bomber, also built by Northrop Grumman. Both aircraft have no fuselage or vertical tail. Their all-wing design eliminates much of the surface area that would cause drag on a conventional aircraft.

It also eliminates many of the surfaces and edges from which radar energy would normally reflect, making a plane detectable. The X-47B can carry slightly more than two tonnes of munitions, about one-ninth of the B-2's payload. Using manned aircraft, the 11 carriers operated by the US today are best suited for striking targets at ranges out to about 830 kilometres.

With aerial refuelling, the X-47B could remain on patrol at ranges well beyond 5500 kilometres and stay aloft for 50 to 100 hours - five to 10 times longer than a manned aircraft. This extended reach and ability to stay within range of its target, either for reconnaissance or attack, would allow a dispersed US aircraft carrier force to apply combat power over an enormous area.

Since al-Qaeda's attack on the US in September 2001, the number of military-related drones in service in the US has risen from just a small number to over 7500 - roughly one-third of all US military aircraft.

Despite big cuts that are looming in US defence spending, drones are expected to take less of a hit because of their potential to help maintain US military power and because they are generally cheaper to build and operate than piloted combat planes.

Can China catch the US in drone technology? At China's biennial air show in Zhuhai last month, an imposing fleet of operational and model drones was on show, most of them strikingly similar in appearance to leading US drones.

One of them, the CH-4, which has four under-wing pylons capable of carrying missiles and satellite-guided precision bombs, reportedly has a range of more than 3500 kilometres and is intended for missions over islands disputed between China and its neighbours in the East and South China seas.

A panel of experts advising the Pentagon reported in July that China is ''moving rapidly to catch up - and perhaps ultimately overtake - the West in this rapidly growing and increasingly important sector of aerospace and defence''. The panel, known as the Defence Science Board, said the military significance of China's move into unmanned systems was alarming. ''The country has a great deal of technology, seemingly unlimited resources and clearly is leveraging all available information on Western unmanned systems development,'' the DSB reported.

It said China's plan for Anjian (Dark Sword) represented an aspiration to design something even Western powers did not yet have - a supersonic drone capable of air-to-air combat as well as ground strikes.

The DSB report added that the new Chinese drone design, with its high altitude, could serve as the targeting node for China's anti-ship ballistic missiles aimed at US aircraft carriers.

The writer is visiting senior research fellow at the Institute of South East Asian Studies in Singapore.