Worldwide, drones are in high demand.

• Author: Parsons, Dan

* The U.S. military may be the most high-profile owner and operator of unmanned aircraft, but it is far from the only customer of the controversial vehicles.

There is no continent on earth, save Antarctica, that is not home to a country that builds or is desperately seeking to buy unmanned aerial vehicles, spurred by the much-publicized success of their use in Iraq and Afghanistan.

There are already 4,000 different unmanned aircraft platforms in circulation on the global market.

There are concerns about that level of proliferation, primarily because UAVs can be used for lethal purposes. But only sophisticated models like the Global Hawk and Predator drones, over which the U.S. military and industry holds a virtual monopoly, are capable of such feats. The majority of remotely piloted aircraft will be smaller and perform intelligence, surveillance and reconnaissance missions, analysts agree.

UAVs have been in service for several decades, but they exploded on the scene over the past decade because of their high-profile use by the U.S. military in Iraq and Afghanistan. In the last five years, demand for unmanned aircraft worldwide has grown by double digits annually with U.S. customers, accounting for two-thirds of the market, said Derrick Maple, principal analyst at IHS Industry Research and Analysis.

Such rapid growth is typical of an economic bubble, especially one on the cusp of bursting, Maple said. But international demand for UAVs will more than offset a downturn in military spending until the U.S. domestic market for unmanned systems grows to fill the gap.

"Typical of a market at this state of its life cycle, this high level of growth is not sustainable, especially as these [U.S. military] campaigns undergo a drawdown," Maple said at the Association for Unmanned Systems International's annual program review in March. "However, expanding worldwide opportunities are forecast to offset the reduction and support a growing market over the next 10 years."

The U.S. unmanned systems market will shrink over the next five years but will eventually regenerate, perhaps expanding beyond its current size, Maple said. Still, the United States will remain the largest customer for UAVs, holding on to 45 percent of the global market. The Air Force's requirements for high- and medium-altitude platforms will account for half of U.S. demand, Maple said.

Global defense spending on robotics is expected to exceed $13.4 billion at the end of 2013. Department of Defense spending on unmanned systems accounts for nearly half of that figure, at $6.5 billion. North America, Europe and Asia are the largest markets for unmanned systems, particularly aircraft.

Aircraft account for almost...