Al Qaeda drone attacks on US? Soon it won't be so far-fetched.

A terrorist attack on the nation’s capital using remote-control model airplanes to deliver bombs, as an American Al Qaeda sympathizer arrested in Massachusetts this week is alleged to have planned, may seem far-fetched or silly.

But perhaps not for long. The US, after all, has already been using unmanned planes to attack Al Qaeda targets with deadly accuracy for years.

And now the emerging international market for unmanned aerial vehicles, or UAVs, is exploding, bringing down the cost and expanding the availability of highly capable drone aircraft that could be rigged to deliver explosives, biological or chemical weapons with extreme accuracy – and be difficult or impossible to stop, experts on the subject say.

Groups could smuggle drones into the country or launch them from a ship offshore. Thanks to the development of highly accurate GPS flight systems, even kit-built airplanes could be rigged with explosives and sent hundreds of miles at low altitude, below radar, and crashed into a target, several UAV threat studies have found.

At present, however, the UAV is still America's friend – a potent weapon in the war on terrorism now being deployed to monitor and fight Al Qaeda affiliates from secret drone bases in Africa and the Arabian Peninsula, the Washington Post recently reported.

“There's been so much awareness of the way drones are changing warfare that it’s inevitable that terrorist groups are also keenly aware of drones’ potential,” says John Villasenor, a nonresident senior fellow at the Brookings Institution's Center for Technology Innovation.

“We're familiar with the Predator drone being used against Al Qaeda,” he says. “But it is the much smaller [drone] systems that will be first to proliferate.”

Examples of such systems, though they may not be of immediate use to terrorists, include the Wasp III , a US Air Force-developed micro-drone. It weighs less than a pound and is less than a foot long, but carries two onboard cameras, a GPS receiver and is able to climb to 1,000 feet. In February, a California company demonstrated a prototype called the “Nano Hummingbird,” a video-capable drone weighing two-thirds of an ounce developed with Pentagon funding, according to a study published by Dr. Villasenor this summer.

But the hummingbird is just a tiny blip in the gusher of global spending on UAVs expected to double over the next decade from about $5.9 billion annually to $11.3 billion, according to a recent study by the Teal Group, a Washington-based defense industry market research firm. Total sales of UAVs for that period are expected to total $94 billion, according to the Teal study.

US drone manufacturers are among those pushing to open markets overseas, industry watchers say. So is China, which displayed more than 20 UAV models at the Zhuhai air show in July. More than 50 countries have bought drones for surveillance, with a number ramping up the development of weaponized versions.

“Inevitably this technology is going to spread and the US can’t really stop that,” says Philip Finnegan, Teal Group's director of corporate analysis. “Inevitably non-state actors will try to get control of it. There are threats, not just that someone would get a drone on their own, but that they might take control of others’ drones.”

Today the UAV or drone most familiar to the public is the “Predator,” a US-built weapon extensively used by the US forces in Afghanistan and Iraq to hunt terrorists. That missile-carrying drone is 27 feet long with a wingspan of 49 feet, can climb to 25,000 feet, and fly for 40 hours at time at about 80 miles per hour. It has radar, radio, and surveillance video capabilities – and can carry a 450-pound payload.

But the hulking Predator belies the increasingly intense development of miniature and slightly larger tactical drones in dozens of countries. Tactical UAVs include the RQ-7 Shadow, an 11-foot long US military drone with a 14-foot wingspan used widely for surveillance in Iraq. Even smaller minis, like the Raven – are small enough to be thrown aloft by an individual soldier and can then fly for more than an hour surveying the battlefield day or night.

But what if such technology were harnessed for other purposes? Drone use is, too, an ethical minefield.

“Our dependence on the Predator, particularly as a tool for targeted assassinations, raises a whole set of legal and ethical issues that many people are concerned about coming back to haunt us,” says Dennis Gormley, a senior lecturer on international security and intelligence studies at the University of Pittsburgh.

“There's a growing realization that UAVs are spreading globally, and that certain state and non-state actors might want to use them against us,” he adds. “That's probably inevitable – and the example in this FBI sting operation is just one small example of that.”

The FBI alleges that Rezwan Ferdaus, the Al Qaeda sympathizer, planned to buy, for $3,000, a 68-inch long, 1/10th-scale McDonnell Douglas F-4 Phantom II. The plane, he allegedly told informants, could carry 10 to 12 pounds of plastic explosives at up to 160 miles per hour. It could come equipped with a GPS system to automatically guide the plane, he allegedly said. He also planned to buy two F-86s, one of which he already possessed at the time of his arrest, which have similar capabilities.

His plan, which included detailed diagrams, was to crash the F-4 into the Capitol dome and the two F-86s into the Pentagon to make a statement and kill as many as possible, an FBI affidavit states.

Of course, it’s not clear how much damage the relatively small payloads – a total of 15 pounds of plastic explosive divided among the three model planes – that Ferdaus had in mind might have done. But model-scale UAVs not much larger than those Ferdaus is said to have plotted to use could be used to disperse toxins or chemicals and have been recognized for nearly a decade as a growing threat.

Mr. Villasenor, the Brookings fellow, emphasizes, however, that in the near future terrorists will have more access to smaller, less expensive and more plentiful drones.

“To date, a lot of the drone strikes have been by Predators, which are almost the size of small business jets. But this newer generation of drones can fit in trunk of a car or backpack. Weaponization is moving down the size scale.”

“At this point, these small UAVs are a very limited terrorist threat,” agrees Mr. Finnegan. “It's not going to be easy for them to get a large enough system to do serious damage. But that’s going to change as the technology progresses and number in inventory increases – and particularly as the market for commercial UAVs opens up. We’ll see a proliferation in numbers and the cost coming down. Then you'll have the whole issue of control. Then there’s no longer government control, it’s private industry and individuals.”

Tiny surveillance and weaponized drones can be a huge advantage to military forces, because they’re so difficult to detect or stop. But for that reason “it ought to be sobering since this same technology could be used against us,” Villasenor says.

“We have to recognize that the US's quasi-monopoly on drones is coming to an end,” he says. “We have to think about what that means in terms of how drones impact armed conflict and security in the future. Unfortunately, this arrest in Boston is just the first in what is likely to be multiple news items over the coming years.”