It's nearing midnight on November 12, 2015.
In the centre of the Syrian city of Raqqa, Mohammed Emwazi is in a car with three others driving off into the night.
Some 10,000 feet up in the sky and likely several miles away, two Reaper drones quietly spot and begin to follow the vehicle.
A further 7,000 miles away, in Creech Air Force Base, Nevada, the decision is made to engage.
Invisible in the night sky, the drone launches a Hellfire missile which travels at almost 1,000mph to the car.
Emwazi, better known as Jihadi John, had no idea what was coming.
His killing, meanwhile, was a highly-symbolic moment in the fight against so-called Islamic State.
The Islamist terrorist was the face of several high-profile executions of aid workers and journalists - killings that were brutal, barbaric and sent shockwaves throughout the world.
They couldn't have been in greater contrast to the calculated killing of Emwazi himself, which took months of rigorous intelligence work by British and US experts, who would ultimately give the order to finally take him down from halfway across the world.
Drones have opened up new possibilities for warfare and defined the conflict against ISIS.
It would have been substantially more difficult and more dangerous to kill Emwazi without drone technology.
In 2014 Syria was in the middle of a bitter civil war and ISIS were powerful. Putting boots on the ground was completely out of the question.
The precision 'targeted killing' strikes enabled by drones - and the safety they provide the people who operate them - is very attractive to politicians.
Yet despite these clear tactical advantages, drones have become one of the most controversial tools of modern warfare.
Listen to the fourth episode of 'Weapons That Changed The World' in full below...
Unmanned flying weapons didn't start with drones. The use of military hot air balloons dates back to second-century China, where lanterns would be lit and released above the battlefield to warn of enemy troops. We now call these 'Chinese lanterns'.
It could be argued that the use of drones for surveillance, meanwhile, can be linked back to the French Revolutionary Wars and the American Civil War.
In these conflicts, manned flying hot air balloons started the powerful practice of aerial reconnaissance.
Balloons had a deadlier use though. In 1849 the Austrian Empire launched 200 pilotless, bomb-carrying hot-air balloons against Italian forces.
In World War II the Japanese used fire balloons - hydrogen-filled unmanned balloons that would carry antipersonnel and incendiary bombs - to cause fires in American and Canadian cities.
These were the first intercontinental weapons and although they caused little damage they did spook the American government enough to try and cover up their existence to the American public.
While balloons were effective as surveillance and early communication devices, their unmanned nature meant they could only cause so much damage.
Once they were up in the air, there was little you could do to control them.
The US Army, however, had started development of the Kettering Bug late during World War I - an unmanned radio-controlled 'flying missile'.
Drone production then flourished in World War II, with products like the mass-produced 'Radioplane' used to train anti-aircraft gunners.
The drone continued to develop throughout the 20th century, being used regularly for surveillance in conflicts like the Vietnam War and the Yom Kippur War.
However, the use of drones as we understand them today started with Predator drones.
The General Atomics MQ-1 Predator was developed in the mid-90s, although it wasn't until the early 2000s that armed versions began being built.
The first test, on February 16th, 2001, deep in the Nevada Desert, saw a dummy Hellfire missile fly into a disused tank.
Only a few weeks later the first live missile test was successfully conducted - just months before the 9/11 terrorist attacks.
The coordinated attacks on the Twin Towers would go on to define the decade. The War on Terror that would follow would, in turn, become defined by drone warfare.
Drone strikes in Afghanistan began shortly after 9/11. Information surrounding these strikes is highly secretive and media reports provide different names as to who was the target of the first drone strike in Afghanistan.
However, one of the first drone strikes was almost certainly against the Taliban leader Mullah Omar. Omar had strong family ties with Bin Laden, with both men having fought in the against Soviet Union forces in the 80s. They reportedly even went on fishing trips together.
The leader of the Afghan Taliban was a high priority target for the US. CIA analysts had tracked Omar and identified his house in the city of Kandahar using a Predator drone.
When the Taliban leader passed between buildings the Americans could strike. However, while the Predator was an effective surveillance tool it was still in its infancy as a weapon.
When the order came a Hellfire missile was fired and struck a vehicle, killing multiple bodyguards but completely missing Omar.
He would go on to die in hiding, of natural causes, in 2013. To say this strike was a missed opportunity would be an understatement.
Despite this botched early attempt, the effectiveness of targeted drone strikes would substantially increase.
Data provided by the Bureau of Investigative Journalism shows that since 2015 there have been nearly 4,000 strikes in Afghanistan alone.
Many of the leaders of Islamist groups, including ISIS and Al-Qaeda, have fallen to drone strikes. Brutal terrorists responsible for the deaths of thousands could now be taken out by Predator drones.
They and the larger Reaper drones - introduced in 2007 and used by the RAF to this day - could be used for operations in countries ranging from Afghanistan to Pakistan to Iraq and Somalia.
However, as proved by the failed attempt to take down Mullah Omar - drone strikes can be messy.
On the death of Mohammed Emwazi, one US official told reporters
"We are 99% sure we got him."
The drone that targeted him would have circled around the sky for hours afterwards seeking to confirm the kill.
Although the strikes could take out any terrorist leader given the chance, there can often be doubt over whether the person attacked is, in fact, the true target.
It's estimated that in Pakistan alone between 424 and 969 civilians were killed by drone strikes from 2004 onwards.
Around 200 of those are believed to have been children.
Collateral damage is nothing new in warfare. The doctrine of double effect - that if doing something morally good has a morally bad side-effect it's ethically OK to do it, providing the bad side-effect wasn't intended, was outlined by Thomas Aquinas in the 13th century.
Critics of the theory that drones are somehow different to other combat technology point to civilians' deaths, however.
They argue that these statistics counteract what they believe is the myth of targeted killing.
However, even some counter-terrorism experts have questioned the effectiveness of drones, arguing that they cause instability rather than security.
By unintentionally killing innocent civilians on their home soil some former US Air Force service members have even gone so far as to call them 'recruitment tools for ISIS'.
Those defending the use of the strikes would argue that although civilians do die, far fewer do so that would in conventional warfare.
But do drone strikes, in fact, create more terrorists than they kill?
The legality of drone strikes has also come into question. The use of drone strikes against a country's own citizens is controversial both in the UK and the US.
Gavin Williamson, shortly after his appointment as defence secretary, argued that Britons who have fought for ISIS abroad should be:
"Hunted down and killed."
Barack Obama in 2013 defended his authority to use drone strikes to kill Americans on US soil.
A year earlier, digital artist, Josh Begley developed an app that if downloaded would send the user a push notification every time a drone strike was launched by the American military.
Between updates from social media and other apps users would receive messages like "15 people were on their way to a wedding when a US drone 'missed its target', killing 12".
The app proved controversial, with Apple rejecting it multiple times citing "excessively objectionable or crude content".
One thing is certain, however. The use of drones in war has been far cheaper and safer for Western governments and their militaries than their equivalents in past years.
Drone pilots are far less likely to suffer from PTSD than traditional pilots, although many do still suffer emotional and psychological stress.
What Josh Begley's app points to, though, is how drones have made warfare more distant and removed from everyday life.
The wounds of past wars are very visible on television and in the stories and injuries of service personnel and their families.
One might question: does drone warfare remove these wounds once again, returning warfare to an unseen fight in a faraway land?