Last Friday, while armed militants were attacking sites across Paris, an ISIS leader in Libya was being targeted from the sky. Pentagon Press Secretary Peter Cook reported the next day that Abu Nabil, a senior ISIS leader had been killed in an air strike.

The Wall Street Journal added that the Libyan ISIS leader was struck by a missile fired from an F-15 fighter jet, followed by a second strike from an unmanned vehicle, an Air Force MQ-9 Reaper — a drone.

The attack on Abu Nabil was just the most recent instance of an ISIS figurehead in the Middle East being targeted and killed, at least in part, remotely.

The previous day, Mohammed Emwaz — also known as Jihadi John, the ISIS executioner with the British accent — was reportedly killed while getting into a car in the ISIS stronghold of Raqqa, Syria. His vehicle was struck by two Hellfire missiles fired from an American Reaper.

“For us, it was a fairly routine HVI strike,” Army Col. Steven Warren told reporters at a Pentagon press conference via video link. HVI is the acronym for High Value Individual. “As you know," he continued, "we have killed, on average, one mid- to upper-level ISIL leader every two days since May.” And many of those kills have been accomplished with the help of drones, performing surveillance or firing weapons.

MQ-9 Reapers are flown remotely by two-person teams controlling the aircraft, their cameras, targeting lasers and weapons via communications links. Round-the-clock coverage of a target is accomplished by using a group of four Reapers: one flying above the target, one en route to replace it, one returning to its base for maintenance and refueling, and one on the ground being readied. The drone aircraft are based at regional runways, as close to their targets as possible. The drone pilots work from secure locations such as Creech Air Force Base in Nevada, more than 7,000 miles away.

The use of drones to strike individuals raised a public outcry in 2011 with the targeted killing in Yemen of the American cleric and al-Qaeda firebrand Anwar al-Awlaki. In August this year, Britons expressed outrage over the killing of two British subjects, Reyaad Khan and Ruhul Amin, in a vehicle near Raqqa. Criticism of attacks on high-ranking ISIS members has been buried under the heaps of praise for their precision and lethality.

As the air war against ISIS builds, drones are playing a significant role. “But not as significant as they should be playing,” notes Richard Whittle, author of Predator: The Secret Origins of the Drone Revolution. Whittle says the Reaper is well-equipped for missions such as stalking and targeting individuals. "It carries a daylight camera, an infrared camera and radars. It also carries four Hellfire missiles and two 500-pound bombs. ... You can keep [it] in the air for days at a time, and so it can be very useful when a target is found,” he says.

But finding a target in the vast area controlled by ISIS isn't easy. Especially when relatively few remotely piloted aircraft are in the sky.

"The US Air Force owns 160 Predators and 140 Reapers, but they're not all available to fly combat missions," notes Whittle. "And the US Air Force is actually very short of Reaper pilots. They've told Congress that, in the next fiscal year, they're going to be about 400 short of the 1,200 they need, because you also have to have pilots in the seat around the clock."

Three piloting crews are needed, in 8-hour shifts, to fly a round-the-clock drone mission. “The Air Force has been forced, now, to do 12-hour shifts, six days a week,” says Whittle, “and people are leaving because they don't like those hours."

Whittle, a Global Fellow at the Woodrow Wilson Center in Washington, DC, cautions that while drones can be efficient fighting machines, their best use is surveillance and painting targets. The US Air Force, Army, Navy and Marines — all part of Operation Inherent Resolve — rely on bigger, faster aircraft with greater weapons capacity to attack ISIS. "The most important role of the drone is not actually to deliver ordnance on targets," Whittle says. "They are THE way to [fire] on targets that you want to stalk for a long time, as was the case with Jihadi John, I think. But they're not the way to cause the kind of destruction that will stop a fighting force that has 20,000 men carrying arms."

While drones are getting more attention as they target high-profile individuals, they are not going to win the war by themselves. "Even if you were to produce hundreds and hundreds more drones," says Whittle, "I don't think that would be the answer. I’m not enough of a military expert or strategist to know the magic formula for winning this war. But it seems, from where I sit, that it's going to require troops on the ground. I don't think they necessarily need to be American troops, but I don't think that you can win this war from the air.”