When 26-year-old American physics graduate Rezwan Ferdaus was arrested in Boston last month, charged with scheming to crash an aircraft laden with plastic explosives into the United States Capitol or the Pentagon, the alleged "jihad" plot had one salient feature: the deadly payload would be carried in a pilotless, remote-controlled plane, or drone.
While simple drones can be purchased cheaply by mail order in the US, the Government usually claims a monopoly on assassination via drones or Unmanned Aerial Vehicles (UAV). On September 30, Hellfire missiles launched from Predator drones and directed by CIA pilots on an Arabian Peninsula base killed Anwar al-Awlaki, al Qaeda's propagandist, and Samir Khan, both US citizens, as they stopped their truck for breakfast in Yemen. Bomb-maker Ibrahim Hassan al-Asiri may also have been slain.
Al-Awlaki's 17-year-old son was reportedly killed in a similar drone strike on October 14. And US officials have confirmed that a Predator was used to fire on Muammar Gaddafi's convoy outside Sirte, shortly before the Libyan leader was killed.
Drone attacks are now a regular part of the US counter-terrorism arsenal. "We've carried out well over 250 attacks in Pakistan," says Peter Singer, whose book Wired for War: The Robotics Revolution and Conflict in the 21st Century explores the implications of this tactical shift.
More than 100 US attacks were launched against Gaddafi's forces in Libya and other strikes have been carried out in Iraq, Yemen, Afghanistan and Somalia.
It is a weirdly dehumanised form of warfare. Pilots at Creech Air Force base in Nevada, northwest of Las Vegas, use computers to identify targets in real-time, then direct Predator and Reaper drones to fire missiles and kill Taleban and al Qaeda fighters a world away in Afghanistan.
"As one of the pilots put it to me," says Singer, "you wake up, go to work, spend 12 hours putting missiles on targets, killing enemy combatants, then you get back in your car, drive home and talk to your kids about their schoolwork."
The major risk is carpal tunnel syndrome, or a traffic accident en route to or from work, although post-traumatic stress can reportedly rival combat levels.
Singer says the pilots are in the vanguard of a robotic revolution, where drones are changing the face of warfare as fundamentally as gunpowder or the atomic bomb.
Like the World War I triplane, drones are in their infancy. Singer offers a parallel used by Bill Gates: robotics are currently where personal computers were in 1980. They inhabit a rapidly evolving military environment. As artificial intelligence enters the mainstream, leaders may have to ask: should robots kill without a direct order?
Cameras mounted on drones to feed real-time intelligence to humans can watch a door to see if it opens or follow footprints. Facial recognition software may also one day identify targets. "That turns over a big part of the decision-making process to machines ... the key isn't so much what's technologically capable. It's what do you think is politically, morally and legally justifiable."
Such concerns (and surveillance by police drones raises privacy issues) are a sideshow to what feels like an arms race as about 45 nations, including Britain, China, India, Russia, Israel, Iran, Singapore and Australia, join the drones club.
"This year, the Pentagon will buy more unmanned aircraft than manned and train more UAV pilots than traditional bomber and fighter pilots combined," General David Petraeus, head of US Central Command, said in January.
He said the US, which operates about 7000 drones,"can't get enough". They are cheap compared with jets and, if they crash, no pilots are lost or captured, a political plus.
Besides Reapers and Predators, this fleet includes the small jet-size Global Hawk and the hand-launched Raven. The Switchblade, about the size of "a rolled-up magazine", slams into the target and explodes. Designed for close-quarter combat, it has been used against Taleban in Afghanistan.
Complex drones such as Boeing's stealth prototype, the Phantom Ray, are military-industrial projects. But low-end drones may be attractive to non-state actors.
In 2006, Hezbollah deployed armed drones, supplied by Iran, in the Lebanon war with Israel. They were not used, but Israeli F-16s risked stalling when they decelerated in efforts to shoot them down. But in 2004 and 2005, Hezbollah flew drones into Israeli airspace and photographed a Patriot missile site.
In asymmetric warfare, where insurgents or terrorists take on states, drones are a game-changer and likely to remain so as ideology, climate change, population growth and competition for resources fuel conflict.
They are also helping shape the legal and ethical climate in which these 21st-century wars will be fought. There is growing debate on whether the al-Awlaki and other US drone assassinations set an unlawful standard which may stoke global tensions.
Last year, the United Nations Special Rapporteur for Extrajudicial Executions questioned US drone strikes against people in nations the US was not at war with (the last nation the US declared war on was Romania in 1942), amid criticism the extrajudicial killings amounted to murder. The number of insurgents, terrorists and civilians killed is uncertain.
According to a report this week by the UK-based Bureau of Investigative Journalism, the US has launched 300 strikes - 248 in the Obama Administration - since June 2004 against Pakistan alone, with total deaths ranging from 2318 to 2912, of whom between 386 and 775 were civilians.
Despite reports that the attacks are inciting hatred of the US and aiding al Qaeda recruitment - classic blowback, where covert actions reap unintended results - the US is intensifying drone attacks.
"The US has the authority under international law, and the responsibility to its citizens, to use force, including lethal force, to defend itself, including by targeting persons such as high-level al Qaeda leaders who are planning attacks," the State Department's legal adviser, Harold Koh, insisted last year.
But Dennis Gormley, a US intelligence community veteran, a senior research fellow at the University of Pittsburgh and the author of Missile Contagion, fears US policy may set a tactical precedent for strikes by other states. "Was capturing al-Awlaki any more difficult than capturing Osama bin Laden?" he asks. "We chose to kill Bin Laden. But we could have captured him. There's no doubt about that."
Indeed, US planners had to decide whether to obliterate Bin Laden's Abbottabad compound with a bomber strike - Hellfire missiles used by drones were designed to destroy tanks, not compounds - or send in special forces. Ultimately, the latter course was used to guarantee Bin Laden was identified, although a drone did surveillance.
Before 9/11, extrajudicial killing was outlawed as US policy, after the 1975 Church Committee examined CIA plots against Haiti's Francois "Papa Doc" Duvalier, the Congo's Patrice Lumumba, who was killed, Fidel Castro - one farcical idea was to kill the Cuban leader with an exploding cigar - and other leaders.
But in the aftermath of 9/11, says Gormley, the Bush Administration looked at Article 51 of the UN Charter, which gives states the legal right to respond to imminent threat by taking pre-emptive action, and elevated that response into a national doctrine of preventative action.
The Bush Administration's "One per cent Doctrine" legitimised almost any action against the smallest risk, as the logic of preventative action went global. Gormley cites Russia, Iran, North Korea, Israel - which has a long history of Mossad hits abroad against enemies - and India.
And then there's the question of "hot pursuit"; chasing enemies into foreign territory, a US policy since 19th-century intrusions into Mexico during the Indian Wars and against Mexican revolutionary Pancho Villa in 1916. But hot pursuit against whom? The State Department and the Pentagon are locked in debate about whether drones should be used to kill Taleban foot soldiers or al Qaeda offshoots in Somalia and Yemen, or just leaders like Bin Laden or al-Awlaki. The State Department prefers the latter target.
At the same time, a report in the Washington Post that the US plans to build a "constellation of secret drone bases for counter-terrorism operations in the Horn of Africa and the Arabian Peninsula", including facilities in Ethiopia, the Seychelles, Djibouti and on the Arabian Peninsula, raises the ante on the State versus Pentagon strategy.
"There's no doubt the debate has been precipitated by this expansion," said Gormley. "And in Somalia it's not clear that there's a US agreement with a legitimate authority to do these things." Indeed, it isn't clear that Somalia, a classic failed state, has a legitimate authority. And protests in Yemen raise doubts as to who will be in charge.
A recent post on the New York Review of Books blog, by David Cole from Georgetown University's Law Centre, asked what would happen if Russia used drone strikes on the US to kill individuals deemed to pose "a threat to Russia's security".
Despite the belief Russia orchestrated the 2006 murder, by radiation poisoning, of ex-KGB dissident Alexander Litvinenko in London, the Kremlin is unlikely to launch a drone strike on the US.
But robot-backed realpolitik by, say, India, Russia or Iran could cow Kashmiri, Chechen or Kurdish insurgents. Meanwhile, Latin American nations are pondering how to regulate police actions using drones, such as a Brazilian-Colombian operation in August, when jets bombed a drug-cartel airstrip under UAV surveillance.
Fearful that robots will sanitise and escalate combat, human rights activists and robotic engineers have created the International Committee for Robot Arms Control. Armed robots still have a "human in the loop", warns the ICRAC, but "there is an inexorable drive to create autonomous robots that can choose their own targets and kill them".
US drone strikes in Pakistan since June 2004
Maximum estimated number of deaths
Maximum estimated number of civilians killed
Source: Bureau of Investigative Journalism