Pacifists​ are rare. Most people believe that lethal violence may be used in self-defence, or the defence of others, against potentially lethal threats. Military action is justified by a collective institutional version of this basic human right, which sets an outer limit on the right to life. Lethal aggressors who cannot be stopped by lesser means are liable to lethal attack, and this does not violate their right to life so long as they remain a threat. Killing in self-defence is distinct from execution, the killing of someone who is no longer a threat as a punishment for past conduct. It is also usually distinct from assassination, which can be carried out for a wide range of reasons: revenge, political or religious hatred, nationalistic passion and so forth – though occasionally someone who is a lethal threat to the assassin or his community may be targeted.

The development of drone warfare has put these distinctions under strain, and that helps to explain the visceral reaction many people have against it, in spite of its being much less destructive than more traditional forms of military violence. Drones, or UAVs (unmanned aerial vehicles), are more selective in the killing of enemies, produce less collateral damage to non-combatants and impose no physical risk to those who pilot them, since they are sitting in a control station thousands of miles away. Who could ask for more?

In Objective Troy, Scott Shane explains why Barack Obama, when he became president, favoured drone warfare as his chief anti-terrorism tactic over the conventional wars of his predecessor:

The number of al-Qaida plotters whose aim was to attack Americans was in the hundreds. Yet several hundred thousand Iraqis and Afghans, and some four thousand American troops, had died in the two big wars since 2001 … The drone, it seemed, if used judiciously, offered a way to scale the solution to the problem, picking off America’s real enemies one by one.

‘Let’s kill the people who are trying to kill us,’ Obama would say.

One of those people was Anwar al-Awlaki, an American citizen who had spent half his life in the US and who, when Obama came to power, was operating out of Yemen as a leading member of al-Qaida in the Arabian Peninsula (AQAP). Shane’s fascinating book interweaves narratives of Awlaki’s life and of the legal and military developments that culminated in his killing by a drone strike on 30 September 2011. Shane, a national security reporter for the New York Times, bases his account on extensive interviews, dogged research, and years spent closely tracking the course of these events, and he poses the important questions of justification, legal and moral, that US actions have provoked.

Awlaki was a member of a prominent, pro-American Yemeni family, born in the US in 1971 while his father was doing graduate work in agricultural science on a Fulbright scholarship (the father later served as Yemen’s minister of agriculture). The family returned to Yemen in 1977, but after finishing school there Awlaki came back to study engineering at Colorado State University. It was in the small Muslim community there that he made the contacts that led to his dedication to conservative Islam, leaving behind the merely conventional religion of his family. After completing his degree he abandoned engineering to become an imam, and held posts at mosques in Denver, San Diego and Falls Church, Virginia, a suburb of Washington, where he was at the time of the attacks of 11 September 2001. He was by then becoming widely known for his preaching, circulated first on cassettes, then on CDs and eventually on YouTube.

At the time, he condemned the 9/11 attacks, and although he also expressed concern over the general suspicion of Muslims that followed, there was no sign yet of political radicalism. Still, he came under FBI surveillance because two of the 9/11 attackers had attended his mosque in San Diego and even met with him individually a few times. Though the FBI concluded that there was no evidence of his involvement in terrorism, their surveillance uncovered his regular patronage of prostitutes in Washington, and when he was tipped off about this by an escort service, he decided in 2002 to leave the country, fearing that exposure would ruin his career as a prominent exponent of conservative Islam.

Back in Yemen he extended the reach of his preaching through the internet, and in response to the wars in Afghanistan and Iraq gradually moved towards the view that it was the duty of every Muslim to resist the West’s aggression, by violence if necessary. His fluency in English and his rhetorical gifts were making him the world’s most prominent advocate of radical jihad, and many of those arrested for planning or carrying out terrorist attacks cited his influence. But Awlaki wasn’t only a propagandist: in 2009 he became personally involved in AQAP’s plots. He was approached by one of his internet fans, Umar Farouk Abdulmutallab, the Nigerian who became the ‘underwear bomber’, and arranged for him to be fitted in Yemen with an explosive device that got through airport security but failed to detonate when Abdulmutallab lit the fuse as his plane was about to land in Detroit on 25 December 2009. It was from him that the US authorities learned about Awlaki’s role, which included arranging the martyrdom video.

This near miss had an electrifying effect on the year-old Obama administration. As Shane remarks,

Like Bush and his advisers – indeed, like the American people – Obama and his aides had themselves been radicalised by the threat posed by Islamic radicals. Before 9/11, anyone proposing to use missiles in a country where we were not at war to kill suspected terrorists week after week would have been met with strong opposition. The Bush administration, in fact, had repeatedly and explicitly condemned Israel’s practice of killing Hamas leaders and other militants with missiles and other weapons.

These scruples did not survive 9/11. Predator drones armed with Hellfire missiles were used for targeted killings first in Afghanistan, and then outside war zones, in Yemen and the tribal area of Pakistan – and the programme was embraced by Obama. On 5 February 2010, with the support of a secret legal opinion from the Department of Justice, Awlaki was added to the kill list, under the codename Objective Troy.

The legitimacy of drone warfare has been persistently contested, by Amnesty International and Human Rights Watch among others, on multiple grounds: 1) that those targeted may not be combatants under the laws of war; 2) that the intelligence used to identify and locate targets is often unreliable; 3) that the concept of an ‘imminent threat’ used as the basis for lethal action has been grossly distorted, beyond the bounds of legitimate self-defence; 4) that there is unacceptable collateral damage to civilians, without acknowledgment or any attempt at compensation; 5) that the targeting of individuals outside a war zone amounts to extrajudicial execution; 6) that the alternative of capture and trial is systematically disregarded; 7) that the remoteness and safety of the drone operators fosters a lighthearted attitude to killing. A further problem is the secrecy of the programme, which has mostly been in the hands of the CIA, and the refusal of the Obama administration to make public either its actions or the principles and intelligence behind them. Twice Awlaki’s father initiated legal proceedings in US courts to challenge the targeting of his son: first when the information leaked out that he had been put on the kill list, and then again after he was killed. In both cases the government successfully resisted judicial review of the drone programme on the ground that such military decisions are beyond the jurisdiction of the courts. Shane writes:

In June 2010, after reporting that Awlaki had been added to the kill list, I filed a request under the Freedom of Information Act for all Justice Department legal opinions on targeted killing. I did not ask for the sensitive intelligence on particular strikes, just for the programme’s legal basis. The Justice Department summarily rejected my request, and when the New York Times and the American Civil Liberties Union sued, the administration took the position that it could neither confirm nor deny the existence of a drone programme in Pakistan, though Obama himself had spoken publicly about it. An appeals court finally ruled in our favour nearly four years after my initial request. We got heavily redacted copies of the two 2010 legal opinions by David Barron and Marty Lederman making the case that it was legal and constitutional to kill Awlaki.

It is a dark twist to this story that Barron and Lederman owed their positions in the Justice Department’s Office of Legal Counsel (OLC) to ‘their scathing analyses’ in the Harvard Law Review of the memos justifying torture and other opinions on national security produced by the OLC under the Bush administration. Obama took notice, and appointed them when he took office. A year later they were given the task of determining as quickly as possible whether it would be legal to kill Awlaki, an American citizen.

Though the demand​ for a legal opinion was triggered by Awlaki’s citizenship, and although Barron and Lederman stressed that their opinion held only that the conditions of legality were met in this particular case, what they said implies a general rationale that counters some of the sceptical concerns listed above. The essence of the case, without intelligence details, was subsequently set out by the then attorney general, Eric Holder, in a secret White Paper which was obtained by a reporter in 2013.

The Justice Department’s main claim was that the killing of a leading member of al-Qaida who is engaged in plotting and carrying out attacks against the United States is justified as an act of national self-defence under the laws of war even if the target is not operating from an active war zone, and that his American citizenship does not immunise him from attack. Since the campaign against al-Qaida is not a conflict with the uniformed armed forces of a belligerent state, the US has to rely on intelligence of various kinds, both to identify individuals as active terrorists and to locate them. But that is the inevitable character of combat against a small, mobile organisation whose warriors are not organised into an army, and whose cells may be located anywhere. (As an alternative to the laws of war justification, the US was also prepared to use the analogy of police action against a lethal threat. If a sniper is shooting people from a protected vantage point that prevents him from being captured, it is permissible to kill him to stop him killing more people.)

Yet those justifications do not dispel the persistent sense that targeted killings are executions rather than acts of self-defence. Shane calls the killing of Awlaki ‘an execution without the formalities of indictment, trial and sentencing’, and there is the same suggestion in Obama’s statement, when he announced the killing of Osama bin Laden, that ‘justice has been done.’ That was not a drone strike, of course, and theoretically it could have resulted in the capture rather than the killing of bin Laden. But the aim of retribution for 9/11 is unmistakeable.

The CIA had a secret programme of assassinations (targeting Fidel Castro, for example), which was ended by executive order after being exposed in hearings conducted by Senator Frank Church in the 1970s. But Obama’s Justice Department insisted that a drone strike against Awlaki would not be an assassination, or an extrajudicial execution, or a deprivation of life without due process of law, as prohibited by the Fifth Amendment. Due process, the White Paper said, need not mean judicial process: in a case like this, the determination by ‘an informed, high-level official of the US government … that the targeted individual poses an imminent threat of violent attack against the United States’ would suffice, even if it was based on secret intelligence. In the case of al-Qaida, the Justice Department argued that the concept of imminent threat should be extended to apply to anyone who is committed, over the long term, to implementing lethal attacks against the US – since in order to counter the threat it is necessary to be able to stop it at any point in the course of its planning, preparation or execution, rather than waiting till it is about to be executed. This is in a way comparable to the legitimacy, in warfare, of attacking enemy forces at all times, whether or not they are actively fighting – so long as they have not surrendered.

Two other conditions were specified: capture must be unfeasible and the operation must ‘be conducted in a manner consistent with applicable law of war principles’ including the minimisation of collateral damage. Shane observes that the potential cost in American lives of an attempt to capture someone like Awlaki makes it unsurprising that this option was consistently dismissed as unfeasible, once drone strikes became available. As for collateral damage, there have been some horrible disasters, especially when groups of completely innocent civilians were targeted by mistake. Yet in contrast with the Second World War, when civilians were deliberately targeted by the US in huge numbers, and Vietnam, when there was little attempt to limit collateral damage to non-combatants, the current hostilities seem to involve a genuine if only partly successful effort to limit collateral damage to what is both unavoidable and proportional to the value of the military objective. In this vein of proportionality, Obama frequently appealed to the civilian deaths that would occur in a successful terrorist attack to justify the risk of collateral damage in an anti-terrorist strike designed to head it off.

‘By comparison with the two big ground wars Obama had inherited,’ Shane writes, ‘the toll of non-combatants killed in drone strikes was very small – hundreds, versus hundreds of thousands.’ Nevertheless, this has aroused some of the most fervent opposition, and Shane thinks the relatively small scale of these unintended slaughters helps to explain the outrage:

One factor in the dark portrayal of drones was that stories trump facts in the human imagination, and drone strikes produced compelling stories. The outrage that drones often produced was a visceral reaction to the creepiness of flying killer robots and to the arrogance of casually invading another country’s airspace. But it was also a matter of scale. Saturation bombing in the style of World War Two or Vietnam, or ground invasions of cities like Fallujah in Iraq, produced statistics, not stories; when the number of dead climbed into the thousands, individual tales got lost. Drone strikes, with tolls of two or five or ten, were far easier to grasp and retell as detailed personal accounts. By 2013, survivors of drone strikes began to visit Washington with the support of human rights groups, offering devastating accounts of strikes gone wrong.

This goes with another point: drones are a signal departure from the impersonal destruction that typifies modern technologically advanced warfare, in which the attacker rarely perceives his individual victims. The drone pilot, in contrast, even though he is thousands of miles away, spends many hours closely observing his victim and those near him, waiting for the right opportunity to strike. The stories are about both the killers and the killed.

The 2010 United Nations report on targeted killings by Philip Alston says of drones that ‘because operators are based thousands of miles away from the battlefield, and undertake operations entirely through computer screens and remote audio-feed, there is a risk of developing a “Playstation” mentality to killing.’ But Shane contends credibly that this is not borne out by the experience of those who have done it, and who report an acute and disturbing awareness of the individual humanity of those they observe – not only the non-combatants nearby but also their intended targets. ‘The psychological toll on drone pilots and sensor operators was, paradoxically, far greater than on those who flew traditional fighters and bombers,’ he says.

The personal character of this kind of killing goes all the way to the top. Obama ‘did not trust the agencies carrying out the strikes to grade their own work. He felt it was his responsibility to invest the time – hours each week – to keep abreast of the operations and often to exercise his own judgment about what was justified and what was too risky.’ ‘He was the ultimate arbiter of a “nominations” process to designate terrorists for kill or capture, and there were virtually no captures by American agencies … When the CIA sent word that there was a rare opportunity for a drone strike on a top terrorist – but that his family was with him – it was the president who had reserved to himself the final moral calculation.’ ‘On several occasions, he told aides, with chagrin, that as president he had discovered an unexpected talent. “It turns out,” he said, “that I’m really good at killing people.”’

The president as killer is a chilling new face of the role of commander-in-chief. I suspect that it is the personal, individualised nature of drone warfare that many people find so repellent. It is easier to be resigned to the slaughter of faceless multitudes by conventional missiles, bombs and artillery, with the inevitable attendant collateral damage, in pursuit of legitimate military objectives. War is hell, as we all know. But when the president puts someone on a kill list to be taken out by a precise drone strike, it creates the illusory sense of a more direct responsibility for that death than for the other kind. It feels like an execution, though it is just retail warfare, and the responsibility, individual and collective, is equally great in both cases.

Does it make a moral difference that this kind of killing exposes the killers to no physical risk? Is it a condition on the acceptability of warfare that those who kill should put their lives on the line? That has an emotional plausibility, but it comes from an image of the warrior that applies only selectively. Those who launch missiles or drop bombs are of course legitimate military targets, but often the capacities of the belligerent parties are so asymmetrical that the more powerful of them are in practical terms exempt from risk.

It would have required monumental restraint for the US not to invade Afghanistan after 9/11; but a much more narrowly targeted campaign against al-Qaida, abetted by drones, could probably have achieved as much against the terrorist threat at far less cost. It would have left the Taliban in power, but freeing Afghanistan from that tyranny was not the justification for the invasion. Now, after the removal of other tyrants in Iraq and Libya, the base of operations for terrorist networks has only grown. Shane ends his book with an epitaph for Obama’s strategy of limited response: